How to use a simple SWR meter and what it means to your VHF
 

I've seen many posters talk about antennas and know lots of boaters
with antenna troubles and no clue how to see how it's doing, way up
there, so thought I'd stick my neck into the guillotine and give some
basic instructions on what an SWR meter is, what it does, and what it
means after you learn how to use it. This will be all about VHF
marine band, but is the same for any frequency the meter is made for.

FIRST, let me say not all SWR meters are suitable for VHF marine band
use. The reason for this has to do with the directional coupler, the
part that senses power going this way and power going that way built
into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
out of its design range and its directional coupler is too long. Put
using a CB SWR meter out of your mind. It's not a good reading. A
ham radio VHF SWR meter IS acceptable as its range is usually from 140
to 170 Mhz, which includes our VHF marine band. Most boaters will get
the little white Shakespeare VHF power and SWR meter from Waste Marine
or some other overpricing boat shop so that's what I'll use for my
example.

These little passive SWR meters use the RF power of your radio to
power the meter and require no batteries or power source. One guy I
know got no reading and through the meter had dead batteries in it.
There aren't any. His transmitter power amp was kaput....no output.

THE CONTROLS.

The controls on it are quite simple. There's a switch that switches
from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
jack plugged into a 50 ohm dummy load like the guys at the factory did
to calibrate it. Depending on the position of the meter in the line
of a defective antenna system, it might read way low or it might peg
on 1 watt. Consider it fairly accurate if the SWR of the antenna is
quite low (below 1.5 to 1)

So, What's SWR??.....

SWR (pronounced as three letters, unless you're on CB where it's
called "swur" for some reason noone knows) means Standing Wave Ratio.
The keyword there is RATIO, a measurement of the peak voltage found on
the transmission line in one place, compared to the minimum (trough?)
voltage found 1/4 wavelength from that peak in either direction.
These peaks and valleys are caused by reflections of an imperfect or
off-tuned antenna, bad connectors, kinked transmission lines bent too
sharply and a lot of just poor luck. You can watch these waves out by
the seawall. If you toss a rock into the water (transmitter) it
creates waves that expand out in all directions. When the wave
bounces off the seawall, watch what happens. The wave coming in from
the stone bounce off the REFLECTIVE seawall and go BACK towards the
transmitter, a "reflected power" that wasn't absorbed by the wall. As
the reflected waves pass through the incoming waves that haven't
reflected, yet, notice how there is a wave that doesn't move.....a
Standing Wave that has PEAK positions that stand still a set distance
from TROUGH positions, that also stand still.

The same exact thing is going on in your antenna system, every time
you press that button. In electronics, there are two simple devices
that STORE electrons....capacitors that charge (electrostatically) and
inductors that store energy (magnetically). If you doubt this, go out
and pull the spark plug wire off a running Seagull outboard to test
this theory....we'll wait. Ah, I see you're back? Why do you look so
"shocked"? Did it work?

A perfect RF transmission system perfectly transfers the power from
the transmitter to the perfect antenna, which radiates all the power
the transmitter put out into the air, blasting all the recievers with
your fantastic signal so they can hear your pleas for help. These
systems do not exist. The antenna is never tuned to your channel,
only close to your channel (we hope) and the transmission line is that
cheap white crap from Wasted Marine or RatShack, not rigid coaxial
line used by broadcast stations, made to exacting standards. To keep
it short, the line and antenna have "reactance", like that wall. And
it's that reactance (inductance and capacitance) that cause anomolies
that make reflections, like that wall.

What can we do? How can we measure how bad it is?...............

Most marine antennas are sealed up and "pretuned" for open areas. Not
much we can do to "tune" them to the middle of the band. I like old
Metz antennas, made by an old ham company, just because I can trim
that element for best results. It's tunable. That fishing pole of a
fiberglass antenna is actually a little, specially bent wire embedded
inside fiberglass to keep it straight (and disintegrate reliably in
sunshine so you can replace it, often). "Pruning" the tunable antenna
requires us to measure SWR at different frequencies so we can center
its curve up on the band we want for best results.

What "curve"??

An antenna "resonates", where the inductance balances out the
capacitance and acts like a radiating resistive load, over a fairly
large range of frequencies, not just one. Lucky for us.....it can be
made to pass channel 1 and channel 72, fairly reliably, without
retuning like you have to do to change channels on the HF SSB antenna.
The curve looks kinda like this:
| * *
SWR| * *
| * *
| *
Frequency

If we center the best (lowest) SWR up in the middle of the band, it
will have an acceptable SWR (low) on channels on the bottom and top we
want, and are allowed to use. Part of the testing, we will test
different channels across the marine band to get an idea of what YOUR
plot would look like.

So, how do we measure SWR??.............

For the little meter to measure the antenna, it has to be located
INLINE with the RF power, between the transmitter and antenna.
IDEALLY, we'd like to adjust the antenna with the SWR meter located
between the transmission line, antenna end, and the antenna's coax
connector. Obviously, sometimes, this is not practical for a simple
test. However, the further you are from the antenna, back down the
transmission line, the less the reading is about the antenna SWR and
the more the reading is about the cable losing the signal (attenuation
and leakage) and the reactivity of the cable, itself. If we measure
the SWR at the antenna end, the SWR we measure is only about the
antenna. If we measure it where it's easy, at the radio, the reading
is about the antenna AND the cable, so you can't tell which is at
fault if it sucks.

OK, let's assume you're like me, hate heights, weigh too much to haul
up on a winch with less than 6 strong arms on a winch handle and the
bos'n's chair might not like the load, anyways. So, we'll measure the
antenna at the radio end, at least until we find it's all screwed up.
Disconnect the antenna from the radio, with the radio off so you don't
inadvertently transmit into an open which might do harm to the
transmitter.

Now you need a "coax jumper" that didn't come with the meter. Radio
Shack has them, so get one that's just long enough to hook the meter's
RADIO port to the radio so we can still read it and switch the
controls. If you'd like to MOUNT the meter on your panel, buy two
right-angle UHF 90 degree adapters so we can mount the meter on the
front of the panel and the L-shaped connectors will go back through
the panel to connect the cables to. That would let you see power
output every time you keyed the VHF so you'd be SURE it was
transmitting, instead of calling out for a radio check so often. I
leave them in SWR to watch the antenna, here.

Hook the antenna to the antenna jack and the jumper between the Radio
jack and the radio. Turn on the radio and tune it to a commercial
channel not monitored by the DEA or USCG around 40-something. Put the
meter's little switch in the REFERENCE or SET position and turn the
set control all the way to the left, to keep from pegging the meter.
Test at FULL POWER so you can see if something up there is arcing at
FULL POWER (the meter jumps up in SWR if it is).

Key the transmitter and don't talk into the mic. Turn up the SET level
"volume" control until the meter reads FULL SCALE, all the way to the
SET mark. This sets the reference level of the meter to the power
coming out of the radio "under these conditions". Once set to full
scale, flip the switch to SWR and pray it drops all the way to 1 on
the SWR scale (no reflected power) indicating I was a liar and there
IS a perfect antenna system.....Read the pseudo-accurate meter SWR
scale. 1 is the left edge (1:1 standing waves - there aren't any
standing waves because the antenna is perfect). The next mark up is
probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
mic before the cops start looking for you.

What does this mean??

Here's the relative power levels of the major points.

1.0 SWR....no reflected power....all 25W is going out on the air
1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
out and noone notices anything because you couldn't measure 4% out of
the lab.
2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
goes out on the air and STILL noone notices anything unless they are
magicians.
3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
goes out on the air. Someone comparing this antenna with your perfect
antenna just notices a little movement in his S-meter on the other end
if you're weak. 3.0 and above is considered "bad SWR" and something
needs to be fixed.



CB myths........
1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
they get this from? ANTENNA MANUFACTURERS selling new antennas,
that's where. They made millions from this myth. Wanna see a real
broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
http://www.wzpxtv.com/wzpxtransmitter.htm
This a real readout of a powerful +megawatt TV transmitter from WZPX
on Channel 44 (with a nice new digital TV transmitter, too!) The
software company puts it on the net. SWR tonight on the
beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
really high at these power levels. On your boat, it's not. You don't
have thousands of watts coming back down the pipes at you!

Ok, now always turn the SET control back to the left before unhooking
the meter or changing channels. Do it now.....

Ok, make the same measurements on a few channels (not 16, 22A please)
across the marine band. Record your SWR results and make a crude
chart of them plotting SWR measured against channel (frequency) number
like I did above.

Is the lowest SWR near the middle of the channel numbers? No? Does
the curve at least have a low point (dip) inside the marine band?
Yes, but the dip is around Channel 3 and SWR is much higher at Channel
72 (why they could hear you on 16 but not 72 way off). The antenna is
tuned too LOW. If it's tunable, we need to shorten the element to
raise the resonant frequency. If 1 is high SWR and 72 is low, we need
to lengthen the antenna element. Ideal is a curve with its low point
somewhere in the middle of the band with less than 2:1 SWR on any
channel. The curve shows you where the antenna tuning is and how
broadbanded (how many channels will it radiate well).

If you measure this curve up at the antenna before all that cable
attenuates the SWR reading, it will simply be much more pronounced
because the cable attenuates power up as well as it does power down
the mast....making our reading weaker by a bit. AS you can see,
tuning an antenna ISN'T rocket science. If the channels you use are
all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
CABLE OR THE MEASUREMENT, because every antenna has a curve.

Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
trim the antenna the way it shows in the instructions......

You all should be able to measure SWR just fine with the little
meters, now, and have a vague idea of what it means.

Please leave the classroom quietly so's not to wake the four students
in the back row we lost. (Class quietly leaves, instructor slips out
and puts lights out with them still asleep. One once slept right
through lunch....(c;)



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

I prefer a reflected power meter. Much more inruitive than
an SWR meter. Converting from RP to SWR is a simple formula
as well.

Doug, k3qt
s/v Callista

"Larry W4CSC" wrote in message
...
I've seen many posters talk about antennas and know lots of boaters
with antenna troubles and no clue how to see how it's doing, way up
there, so thought I'd stick my neck into the guillotine and give some
basic instructions on what an SWR meter is, what it does, and what it
means after you learn how to use it. This will be all about VHF
marine band, but is the same for any frequency the meter is made for.

FIRST, let me say not all SWR meters are suitable for VHF marine band
use. The reason for this has to do with the directional coupler, the
part that senses power going this way and power going that way built
into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
out of its design range and its directional coupler is too long. Put
using a CB SWR meter out of your mind. It's not a good reading. A
ham radio VHF SWR meter IS acceptable as its range is usually from 140
to 170 Mhz, which includes our VHF marine band. Most boaters will get
the little white Shakespeare VHF power and SWR meter from Waste Marine
or some other overpricing boat shop so that's what I'll use for my
example.

These little passive SWR meters use the RF power of your radio to
power the meter and require no batteries or power source. One guy I
know got no reading and through the meter had dead batteries in it.
There aren't any. His transmitter power amp was kaput....no output.

THE CONTROLS.

The controls on it are quite simple. There's a switch that switches
from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
jack plugged into a 50 ohm dummy load like the guys at the factory did
to calibrate it. Depending on the position of the meter in the line
of a defective antenna system, it might read way low or it might peg
on 1 watt. Consider it fairly accurate if the SWR of the antenna is
quite low (below 1.5 to 1)

So, What's SWR??.....

SWR (pronounced as three letters, unless you're on CB where it's
called "swur" for some reason noone knows) means Standing Wave Ratio.
The keyword there is RATIO, a measurement of the peak voltage found on
the transmission line in one place, compared to the minimum (trough?)
voltage found 1/4 wavelength from that peak in either direction.
These peaks and valleys are caused by reflections of an imperfect or
off-tuned antenna, bad connectors, kinked transmission lines bent too
sharply and a lot of just poor luck. You can watch these waves out by
the seawall. If you toss a rock into the water (transmitter) it
creates waves that expand out in all directions. When the wave
bounces off the seawall, watch what happens. The wave coming in from
the stone bounce off the REFLECTIVE seawall and go BACK towards the
transmitter, a "reflected power" that wasn't absorbed by the wall. As
the reflected waves pass through the incoming waves that haven't
reflected, yet, notice how there is a wave that doesn't move.....a
Standing Wave that has PEAK positions that stand still a set distance
from TROUGH positions, that also stand still.

The same exact thing is going on in your antenna system, every time
you press that button. In electronics, there are two simple devices
that STORE electrons....capacitors that charge (electrostatically) and
inductors that store energy (magnetically). If you doubt this, go out
and pull the spark plug wire off a running Seagull outboard to test
this theory....we'll wait. Ah, I see you're back? Why do you look so
"shocked"? Did it work?

A perfect RF transmission system perfectly transfers the power from
the transmitter to the perfect antenna, which radiates all the power
the transmitter put out into the air, blasting all the recievers with
your fantastic signal so they can hear your pleas for help. These
systems do not exist. The antenna is never tuned to your channel,
only close to your channel (we hope) and the transmission line is that
cheap white crap from Wasted Marine or RatShack, not rigid coaxial
line used by broadcast stations, made to exacting standards. To keep
it short, the line and antenna have "reactance", like that wall. And
it's that reactance (inductance and capacitance) that cause anomolies
that make reflections, like that wall.

What can we do? How can we measure how bad it is?...............

Most marine antennas are sealed up and "pretuned" for open areas. Not
much we can do to "tune" them to the middle of the band. I like old
Metz antennas, made by an old ham company, just because I can trim
that element for best results. It's tunable. That fishing pole of a
fiberglass antenna is actually a little, specially bent wire embedded
inside fiberglass to keep it straight (and disintegrate reliably in
sunshine so you can replace it, often). "Pruning" the tunable antenna
requires us to measure SWR at different frequencies so we can center
its curve up on the band we want for best results.

What "curve"??

An antenna "resonates", where the inductance balances out the
capacitance and acts like a radiating resistive load, over a fairly
large range of frequencies, not just one. Lucky for us.....it can be
made to pass channel 1 and channel 72, fairly reliably, without
retuning like you have to do to change channels on the HF SSB antenna.
The curve looks kinda like this:
| * *
SWR| * *
| * *
| *
Frequency

If we center the best (lowest) SWR up in the middle of the band, it
will have an acceptable SWR (low) on channels on the bottom and top we
want, and are allowed to use. Part of the testing, we will test
different channels across the marine band to get an idea of what YOUR
plot would look like.

So, how do we measure SWR??.............

For the little meter to measure the antenna, it has to be located
INLINE with the RF power, between the transmitter and antenna.
IDEALLY, we'd like to adjust the antenna with the SWR meter located
between the transmission line, antenna end, and the antenna's coax
connector. Obviously, sometimes, this is not practical for a simple
test. However, the further you are from the antenna, back down the
transmission line, the less the reading is about the antenna SWR and
the more the reading is about the cable losing the signal (attenuation
and leakage) and the reactivity of the cable, itself. If we measure
the SWR at the antenna end, the SWR we measure is only about the
antenna. If we measure it where it's easy, at the radio, the reading
is about the antenna AND the cable, so you can't tell which is at
fault if it sucks.

OK, let's assume you're like me, hate heights, weigh too much to haul
up on a winch with less than 6 strong arms on a winch handle and the
bos'n's chair might not like the load, anyways. So, we'll measure the
antenna at the radio end, at least until we find it's all screwed up.
Disconnect the antenna from the radio, with the radio off so you don't
inadvertently transmit into an open which might do harm to the
transmitter.

Now you need a "coax jumper" that didn't come with the meter. Radio
Shack has them, so get one that's just long enough to hook the meter's
RADIO port to the radio so we can still read it and switch the
controls. If you'd like to MOUNT the meter on your panel, buy two
right-angle UHF 90 degree adapters so we can mount the meter on the
front of the panel and the L-shaped connectors will go back through
the panel to connect the cables to. That would let you see power
output every time you keyed the VHF so you'd be SURE it was
transmitting, instead of calling out for a radio check so often. I
leave them in SWR to watch the antenna, here.

Hook the antenna to the antenna jack and the jumper between the Radio
jack and the radio. Turn on the radio and tune it to a commercial
channel not monitored by the DEA or USCG around 40-something. Put the
meter's little switch in the REFERENCE or SET position and turn the
set control all the way to the left, to keep from pegging the meter.
Test at FULL POWER so you can see if something up there is arcing at
FULL POWER (the meter jumps up in SWR if it is).

Key the transmitter and don't talk into the mic. Turn up the SET level
"volume" control until the meter reads FULL SCALE, all the way to the
SET mark. This sets the reference level of the meter to the power
coming out of the radio "under these conditions". Once set to full
scale, flip the switch to SWR and pray it drops all the way to 1 on
the SWR scale (no reflected power) indicating I was a liar and there
IS a perfect antenna system.....Read the pseudo-accurate meter SWR
scale. 1 is the left edge (1:1 standing waves - there aren't any
standing waves because the antenna is perfect). The next mark up is
probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
mic before the cops start looking for you.

What does this mean??

Here's the relative power levels of the major points.

1.0 SWR....no reflected power....all 25W is going out on the air
1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
out and noone notices anything because you couldn't measure 4% out of
the lab.
2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
goes out on the air and STILL noone notices anything unless they are
magicians.
3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
goes out on the air. Someone comparing this antenna with your perfect
antenna just notices a little movement in his S-meter on the other end
if you're weak. 3.0 and above is considered "bad SWR" and something
needs to be fixed.



CB myths........
1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
they get this from? ANTENNA MANUFACTURERS selling new antennas,
that's where. They made millions from this myth. Wanna see a real
broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
http://www.wzpxtv.com/wzpxtransmitter.htm
This a real readout of a powerful +megawatt TV transmitter from WZPX
on Channel 44 (with a nice new digital TV transmitter, too!) The
software company puts it on the net. SWR tonight on the
beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
really high at these power levels. On your boat, it's not. You don't
have thousands of watts coming back down the pipes at you!

Ok, now always turn the SET control back to the left before unhooking
the meter or changing channels. Do it now.....

Ok, make the same measurements on a few channels (not 16, 22A please)
across the marine band. Record your SWR results and make a crude
chart of them plotting SWR measured against channel (frequency) number
like I did above.

Is the lowest SWR near the middle of the channel numbers? No? Does
the curve at least have a low point (dip) inside the marine band?
Yes, but the dip is around Channel 3 and SWR is much higher at Channel
72 (why they could hear you on 16 but not 72 way off). The antenna is
tuned too LOW. If it's tunable, we need to shorten the element to
raise the resonant frequency. If 1 is high SWR and 72 is low, we need
to lengthen the antenna element. Ideal is a curve with its low point
somewhere in the middle of the band with less than 2:1 SWR on any
channel. The curve shows you where the antenna tuning is and how
broadbanded (how many channels will it radiate well).

If you measure this curve up at the antenna before all that cable
attenuates the SWR reading, it will simply be much more pronounced
because the cable attenuates power up as well as it does power down
the mast....making our reading weaker by a bit. AS you can see,
tuning an antenna ISN'T rocket science. If the channels you use are
all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
CABLE OR THE MEASUREMENT, because every antenna has a curve.

Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
trim the antenna the way it shows in the instructions......

You all should be able to measure SWR just fine with the little
meters, now, and have a vague idea of what it means.

Please leave the classroom quietly so's not to wake the four students
in the back row we lost. (Class quietly leaves, instructor slips out
and puts lights out with them still asleep. One once slept right
through lunch....(c;)



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

Care to expand on that ????.................


"Doug Dotson" wrote in message
...
I prefer a reflected power meter. Much more inruitive than
an SWR meter. Converting from RP to SWR is a simple formula
as well.

Doug, k3qt
s/v Callista

"Larry W4CSC" wrote in message
...
I've seen many posters talk about antennas and know lots of boaters
with antenna troubles and no clue how to see how it's doing, way up
there, so thought I'd stick my neck into the guillotine and give some
basic instructions on what an SWR meter is, what it does, and what it
means after you learn how to use it. This will be all about VHF
marine band, but is the same for any frequency the meter is made for.

FIRST, let me say not all SWR meters are suitable for VHF marine band
use. The reason for this has to do with the directional coupler, the
part that senses power going this way and power going that way built
into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
out of its design range and its directional coupler is too long. Put
using a CB SWR meter out of your mind. It's not a good reading. A
ham radio VHF SWR meter IS acceptable as its range is usually from 140
to 170 Mhz, which includes our VHF marine band. Most boaters will get
the little white Shakespeare VHF power and SWR meter from Waste Marine
or some other overpricing boat shop so that's what I'll use for my
example.

These little passive SWR meters use the RF power of your radio to
power the meter and require no batteries or power source. One guy I
know got no reading and through the meter had dead batteries in it.
There aren't any. His transmitter power amp was kaput....no output.

THE CONTROLS.

The controls on it are quite simple. There's a switch that switches
from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
jack plugged into a 50 ohm dummy load like the guys at the factory did
to calibrate it. Depending on the position of the meter in the line
of a defective antenna system, it might read way low or it might peg
on 1 watt. Consider it fairly accurate if the SWR of the antenna is
quite low (below 1.5 to 1)

So, What's SWR??.....

SWR (pronounced as three letters, unless you're on CB where it's
called "swur" for some reason noone knows) means Standing Wave Ratio.
The keyword there is RATIO, a measurement of the peak voltage found on
the transmission line in one place, compared to the minimum (trough?)
voltage found 1/4 wavelength from that peak in either direction.
These peaks and valleys are caused by reflections of an imperfect or
off-tuned antenna, bad connectors, kinked transmission lines bent too
sharply and a lot of just poor luck. You can watch these waves out by
the seawall. If you toss a rock into the water (transmitter) it
creates waves that expand out in all directions. When the wave
bounces off the seawall, watch what happens. The wave coming in from
the stone bounce off the REFLECTIVE seawall and go BACK towards the
transmitter, a "reflected power" that wasn't absorbed by the wall. As
the reflected waves pass through the incoming waves that haven't
reflected, yet, notice how there is a wave that doesn't move.....a
Standing Wave that has PEAK positions that stand still a set distance
from TROUGH positions, that also stand still.

The same exact thing is going on in your antenna system, every time
you press that button. In electronics, there are two simple devices
that STORE electrons....capacitors that charge (electrostatically) and
inductors that store energy (magnetically). If you doubt this, go out
and pull the spark plug wire off a running Seagull outboard to test
this theory....we'll wait. Ah, I see you're back? Why do you look so
"shocked"? Did it work?

A perfect RF transmission system perfectly transfers the power from
the transmitter to the perfect antenna, which radiates all the power
the transmitter put out into the air, blasting all the recievers with
your fantastic signal so they can hear your pleas for help. These
systems do not exist. The antenna is never tuned to your channel,
only close to your channel (we hope) and the transmission line is that
cheap white crap from Wasted Marine or RatShack, not rigid coaxial
line used by broadcast stations, made to exacting standards. To keep
it short, the line and antenna have "reactance", like that wall. And
it's that reactance (inductance and capacitance) that cause anomolies
that make reflections, like that wall.

What can we do? How can we measure how bad it is?...............

Most marine antennas are sealed up and "pretuned" for open areas. Not
much we can do to "tune" them to the middle of the band. I like old
Metz antennas, made by an old ham company, just because I can trim
that element for best results. It's tunable. That fishing pole of a
fiberglass antenna is actually a little, specially bent wire embedded
inside fiberglass to keep it straight (and disintegrate reliably in
sunshine so you can replace it, often). "Pruning" the tunable antenna
requires us to measure SWR at different frequencies so we can center
its curve up on the band we want for best results.

What "curve"??

An antenna "resonates", where the inductance balances out the
capacitance and acts like a radiating resistive load, over a fairly
large range of frequencies, not just one. Lucky for us.....it can be
made to pass channel 1 and channel 72, fairly reliably, without
retuning like you have to do to change channels on the HF SSB antenna.
The curve looks kinda like this:
| * *
SWR| * *
| * *
| *
Frequency

If we center the best (lowest) SWR up in the middle of the band, it
will have an acceptable SWR (low) on channels on the bottom and top we
want, and are allowed to use. Part of the testing, we will test
different channels across the marine band to get an idea of what YOUR
plot would look like.

So, how do we measure SWR??.............

For the little meter to measure the antenna, it has to be located
INLINE with the RF power, between the transmitter and antenna.
IDEALLY, we'd like to adjust the antenna with the SWR meter located
between the transmission line, antenna end, and the antenna's coax
connector. Obviously, sometimes, this is not practical for a simple
test. However, the further you are from the antenna, back down the
transmission line, the less the reading is about the antenna SWR and
the more the reading is about the cable losing the signal (attenuation
and leakage) and the reactivity of the cable, itself. If we measure
the SWR at the antenna end, the SWR we measure is only about the
antenna. If we measure it where it's easy, at the radio, the reading
is about the antenna AND the cable, so you can't tell which is at
fault if it sucks.

OK, let's assume you're like me, hate heights, weigh too much to haul
up on a winch with less than 6 strong arms on a winch handle and the
bos'n's chair might not like the load, anyways. So, we'll measure the
antenna at the radio end, at least until we find it's all screwed up.
Disconnect the antenna from the radio, with the radio off so you don't
inadvertently transmit into an open which might do harm to the
transmitter.

Now you need a "coax jumper" that didn't come with the meter. Radio
Shack has them, so get one that's just long enough to hook the meter's
RADIO port to the radio so we can still read it and switch the
controls. If you'd like to MOUNT the meter on your panel, buy two
right-angle UHF 90 degree adapters so we can mount the meter on the
front of the panel and the L-shaped connectors will go back through
the panel to connect the cables to. That would let you see power
output every time you keyed the VHF so you'd be SURE it was
transmitting, instead of calling out for a radio check so often. I
leave them in SWR to watch the antenna, here.

Hook the antenna to the antenna jack and the jumper between the Radio
jack and the radio. Turn on the radio and tune it to a commercial
channel not monitored by the DEA or USCG around 40-something. Put the
meter's little switch in the REFERENCE or SET position and turn the
set control all the way to the left, to keep from pegging the meter.
Test at FULL POWER so you can see if something up there is arcing at
FULL POWER (the meter jumps up in SWR if it is).

Key the transmitter and don't talk into the mic. Turn up the SET level
"volume" control until the meter reads FULL SCALE, all the way to the
SET mark. This sets the reference level of the meter to the power
coming out of the radio "under these conditions". Once set to full
scale, flip the switch to SWR and pray it drops all the way to 1 on
the SWR scale (no reflected power) indicating I was a liar and there
IS a perfect antenna system.....Read the pseudo-accurate meter SWR
scale. 1 is the left edge (1:1 standing waves - there aren't any
standing waves because the antenna is perfect). The next mark up is
probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
mic before the cops start looking for you.

What does this mean??

Here's the relative power levels of the major points.

1.0 SWR....no reflected power....all 25W is going out on the air
1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
out and noone notices anything because you couldn't measure 4% out of
the lab.
2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
goes out on the air and STILL noone notices anything unless they are
magicians.
3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
goes out on the air. Someone comparing this antenna with your perfect
antenna just notices a little movement in his S-meter on the other end
if you're weak. 3.0 and above is considered "bad SWR" and something
needs to be fixed.



CB myths........
1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
they get this from? ANTENNA MANUFACTURERS selling new antennas,
that's where. They made millions from this myth. Wanna see a real
broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
http://www.wzpxtv.com/wzpxtransmitter.htm
This a real readout of a powerful +megawatt TV transmitter from WZPX
on Channel 44 (with a nice new digital TV transmitter, too!) The
software company puts it on the net. SWR tonight on the
beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
really high at these power levels. On your boat, it's not. You don't
have thousands of watts coming back down the pipes at you!

Ok, now always turn the SET control back to the left before unhooking
the meter or changing channels. Do it now.....

Ok, make the same measurements on a few channels (not 16, 22A please)
across the marine band. Record your SWR results and make a crude
chart of them plotting SWR measured against channel (frequency) number
like I did above.

Is the lowest SWR near the middle of the channel numbers? No? Does
the curve at least have a low point (dip) inside the marine band?
Yes, but the dip is around Channel 3 and SWR is much higher at Channel
72 (why they could hear you on 16 but not 72 way off). The antenna is
tuned too LOW. If it's tunable, we need to shorten the element to
raise the resonant frequency. If 1 is high SWR and 72 is low, we need
to lengthen the antenna element. Ideal is a curve with its low point
somewhere in the middle of the band with less than 2:1 SWR on any
channel. The curve shows you where the antenna tuning is and how
broadbanded (how many channels will it radiate well).

If you measure this curve up at the antenna before all that cable
attenuates the SWR reading, it will simply be much more pronounced
because the cable attenuates power up as well as it does power down
the mast....making our reading weaker by a bit. AS you can see,
tuning an antenna ISN'T rocket science. If the channels you use are
all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
CABLE OR THE MEASUREMENT, because every antenna has a curve.

Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
trim the antenna the way it shows in the instructions......

You all should be able to measure SWR just fine with the little
meters, now, and have a vague idea of what it means.

Please leave the classroom quietly so's not to wake the four students
in the back row we lost. (Class quietly leaves, instructor slips out
and puts lights out with them still asleep. One once slept right
through lunch....(c;)



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

Thank you Professor; you explained this operation far more succinctly than I
have. Consider yourself plagarized the next time I am explaining SWR to a
client ;-)

73-
Charlie
JTB Marine Service

How to use a simple SWR meter and what it means to your VHF
 

A RP meter read the amount of watts that are being reflected back
If I hook it up to my VHF and it reads 20 watts forward and 5 watts
reflected, that is bad. 23 forward and 2 reflected is not so bad, etc.
I use a Bird Thruline but there are cheaper ones out there.

Doug

"Erik the Bold" wrote in message
...
Care to expand on that ????.................


"Doug Dotson" wrote in message
...
I prefer a reflected power meter. Much more inruitive than
an SWR meter. Converting from RP to SWR is a simple formula
as well.

Doug, k3qt
s/v Callista

"Larry W4CSC" wrote in message
...
I've seen many posters talk about antennas and know lots of boaters
with antenna troubles and no clue how to see how it's doing, way up
there, so thought I'd stick my neck into the guillotine and give some
basic instructions on what an SWR meter is, what it does, and what it
means after you learn how to use it. This will be all about VHF
marine band, but is the same for any frequency the meter is made for.

FIRST, let me say not all SWR meters are suitable for VHF marine band
use. The reason for this has to do with the directional coupler, the
part that senses power going this way and power going that way built
into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
out of its design range and its directional coupler is too long. Put
using a CB SWR meter out of your mind. It's not a good reading. A
ham radio VHF SWR meter IS acceptable as its range is usually from 140
to 170 Mhz, which includes our VHF marine band. Most boaters will get
the little white Shakespeare VHF power and SWR meter from Waste Marine
or some other overpricing boat shop so that's what I'll use for my
example.

These little passive SWR meters use the RF power of your radio to
power the meter and require no batteries or power source. One guy I
know got no reading and through the meter had dead batteries in it.
There aren't any. His transmitter power amp was kaput....no output.

THE CONTROLS.

The controls on it are quite simple. There's a switch that switches
from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
jack plugged into a 50 ohm dummy load like the guys at the factory did
to calibrate it. Depending on the position of the meter in the line
of a defective antenna system, it might read way low or it might peg
on 1 watt. Consider it fairly accurate if the SWR of the antenna is
quite low (below 1.5 to 1)

So, What's SWR??.....

SWR (pronounced as three letters, unless you're on CB where it's
called "swur" for some reason noone knows) means Standing Wave Ratio.
The keyword there is RATIO, a measurement of the peak voltage found on
the transmission line in one place, compared to the minimum (trough?)
voltage found 1/4 wavelength from that peak in either direction.
These peaks and valleys are caused by reflections of an imperfect or
off-tuned antenna, bad connectors, kinked transmission lines bent too
sharply and a lot of just poor luck. You can watch these waves out by
the seawall. If you toss a rock into the water (transmitter) it
creates waves that expand out in all directions. When the wave
bounces off the seawall, watch what happens. The wave coming in from
the stone bounce off the REFLECTIVE seawall and go BACK towards the
transmitter, a "reflected power" that wasn't absorbed by the wall. As
the reflected waves pass through the incoming waves that haven't
reflected, yet, notice how there is a wave that doesn't move.....a
Standing Wave that has PEAK positions that stand still a set distance
from TROUGH positions, that also stand still.

The same exact thing is going on in your antenna system, every time
you press that button. In electronics, there are two simple devices
that STORE electrons....capacitors that charge (electrostatically) and
inductors that store energy (magnetically). If you doubt this, go out
and pull the spark plug wire off a running Seagull outboard to test
this theory....we'll wait. Ah, I see you're back? Why do you look so
"shocked"? Did it work?

A perfect RF transmission system perfectly transfers the power from
the transmitter to the perfect antenna, which radiates all the power
the transmitter put out into the air, blasting all the recievers with
your fantastic signal so they can hear your pleas for help. These
systems do not exist. The antenna is never tuned to your channel,
only close to your channel (we hope) and the transmission line is that
cheap white crap from Wasted Marine or RatShack, not rigid coaxial
line used by broadcast stations, made to exacting standards. To keep
it short, the line and antenna have "reactance", like that wall. And
it's that reactance (inductance and capacitance) that cause anomolies
that make reflections, like that wall.

What can we do? How can we measure how bad it is?...............

Most marine antennas are sealed up and "pretuned" for open areas. Not
much we can do to "tune" them to the middle of the band. I like old
Metz antennas, made by an old ham company, just because I can trim
that element for best results. It's tunable. That fishing pole of a
fiberglass antenna is actually a little, specially bent wire embedded
inside fiberglass to keep it straight (and disintegrate reliably in
sunshine so you can replace it, often). "Pruning" the tunable antenna
requires us to measure SWR at different frequencies so we can center
its curve up on the band we want for best results.

What "curve"??

An antenna "resonates", where the inductance balances out the
capacitance and acts like a radiating resistive load, over a fairly
large range of frequencies, not just one. Lucky for us.....it can be
made to pass channel 1 and channel 72, fairly reliably, without
retuning like you have to do to change channels on the HF SSB antenna.
The curve looks kinda like this:
| * *
SWR| * *
| * *
| *
Frequency

If we center the best (lowest) SWR up in the middle of the band, it
will have an acceptable SWR (low) on channels on the bottom and top we
want, and are allowed to use. Part of the testing, we will test
different channels across the marine band to get an idea of what YOUR
plot would look like.

So, how do we measure SWR??.............

For the little meter to measure the antenna, it has to be located
INLINE with the RF power, between the transmitter and antenna.
IDEALLY, we'd like to adjust the antenna with the SWR meter located
between the transmission line, antenna end, and the antenna's coax
connector. Obviously, sometimes, this is not practical for a simple
test. However, the further you are from the antenna, back down the
transmission line, the less the reading is about the antenna SWR and
the more the reading is about the cable losing the signal (attenuation
and leakage) and the reactivity of the cable, itself. If we measure
the SWR at the antenna end, the SWR we measure is only about the
antenna. If we measure it where it's easy, at the radio, the reading
is about the antenna AND the cable, so you can't tell which is at
fault if it sucks.

OK, let's assume you're like me, hate heights, weigh too much to haul
up on a winch with less than 6 strong arms on a winch handle and the
bos'n's chair might not like the load, anyways. So, we'll measure the
antenna at the radio end, at least until we find it's all screwed up.
Disconnect the antenna from the radio, with the radio off so you don't
inadvertently transmit into an open which might do harm to the
transmitter.

Now you need a "coax jumper" that didn't come with the meter. Radio
Shack has them, so get one that's just long enough to hook the meter's
RADIO port to the radio so we can still read it and switch the
controls. If you'd like to MOUNT the meter on your panel, buy two
right-angle UHF 90 degree adapters so we can mount the meter on the
front of the panel and the L-shaped connectors will go back through
the panel to connect the cables to. That would let you see power
output every time you keyed the VHF so you'd be SURE it was
transmitting, instead of calling out for a radio check so often. I
leave them in SWR to watch the antenna, here.

Hook the antenna to the antenna jack and the jumper between the Radio
jack and the radio. Turn on the radio and tune it to a commercial
channel not monitored by the DEA or USCG around 40-something. Put the
meter's little switch in the REFERENCE or SET position and turn the
set control all the way to the left, to keep from pegging the meter.
Test at FULL POWER so you can see if something up there is arcing at
FULL POWER (the meter jumps up in SWR if it is).

Key the transmitter and don't talk into the mic. Turn up the SET level
"volume" control until the meter reads FULL SCALE, all the way to the
SET mark. This sets the reference level of the meter to the power
coming out of the radio "under these conditions". Once set to full
scale, flip the switch to SWR and pray it drops all the way to 1 on
the SWR scale (no reflected power) indicating I was a liar and there
IS a perfect antenna system.....Read the pseudo-accurate meter SWR
scale. 1 is the left edge (1:1 standing waves - there aren't any
standing waves because the antenna is perfect). The next mark up is
probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
mic before the cops start looking for you.

What does this mean??

Here's the relative power levels of the major points.

1.0 SWR....no reflected power....all 25W is going out on the air
1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
out and noone notices anything because you couldn't measure 4% out of
the lab.
2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
goes out on the air and STILL noone notices anything unless they are
magicians.
3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
goes out on the air. Someone comparing this antenna with your perfect
antenna just notices a little movement in his S-meter on the other end
if you're weak. 3.0 and above is considered "bad SWR" and something
needs to be fixed.



CB myths........
1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
they get this from? ANTENNA MANUFACTURERS selling new antennas,
that's where. They made millions from this myth. Wanna see a real
broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
http://www.wzpxtv.com/wzpxtransmitter.htm
This a real readout of a powerful +megawatt TV transmitter from WZPX
on Channel 44 (with a nice new digital TV transmitter, too!) The
software company puts it on the net. SWR tonight on the
beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
really high at these power levels. On your boat, it's not. You don't
have thousands of watts coming back down the pipes at you!

Ok, now always turn the SET control back to the left before unhooking
the meter or changing channels. Do it now.....

Ok, make the same measurements on a few channels (not 16, 22A please)
across the marine band. Record your SWR results and make a crude
chart of them plotting SWR measured against channel (frequency) number
like I did above.

Is the lowest SWR near the middle of the channel numbers? No? Does
the curve at least have a low point (dip) inside the marine band?
Yes, but the dip is around Channel 3 and SWR is much higher at Channel
72 (why they could hear you on 16 but not 72 way off). The antenna is
tuned too LOW. If it's tunable, we need to shorten the element to
raise the resonant frequency. If 1 is high SWR and 72 is low, we need
to lengthen the antenna element. Ideal is a curve with its low point
somewhere in the middle of the band with less than 2:1 SWR on any
channel. The curve shows you where the antenna tuning is and how
broadbanded (how many channels will it radiate well).

If you measure this curve up at the antenna before all that cable
attenuates the SWR reading, it will simply be much more pronounced
because the cable attenuates power up as well as it does power down
the mast....making our reading weaker by a bit. AS you can see,
tuning an antenna ISN'T rocket science. If the channels you use are
all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
CABLE OR THE MEASUREMENT, because every antenna has a curve.

Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
trim the antenna the way it shows in the instructions......

You all should be able to measure SWR just fine with the little
meters, now, and have a vague idea of what it means.

Please leave the classroom quietly so's not to wake the four students
in the back row we lost. (Class quietly leaves, instructor slips out
and puts lights out with them still asleep. One once slept right
through lunch....(c;)



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

Good explanation, thanks. Questions:

1) You suggest the possibility of leaving the meter in the line permanently.
Doesn't the impedance bump of a PL-259 speak against that?

2) Since the meter is not type accepted, is leaving it in permanently
technically an FCC violation?

3) I went to
http://www.wzpxtv.com/wzpxtransmitter.htm
and saw a bunch of readouts. The readout labeled "VSWR" (which I think is
the same thing) was reading 0.80 or 0.70.

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?



--
Jim Woodward
www.mvFintry.com


..
..
"Larry W4CSC" wrote in message
...
I've seen many posters talk about antennas and know lots of boaters
with antenna troubles and no clue how to see how it's doing, way up
there, so thought I'd stick my neck into the guillotine and give some
basic instructions on what an SWR meter is, what it does, and what it
means after you learn how to use it. This will be all about VHF
marine band, but is the same for any frequency the meter is made for.

FIRST, let me say not all SWR meters are suitable for VHF marine band
use. The reason for this has to do with the directional coupler, the
part that senses power going this way and power going that way built
into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
out of its design range and its directional coupler is too long. Put
using a CB SWR meter out of your mind. It's not a good reading. A
ham radio VHF SWR meter IS acceptable as its range is usually from 140
to 170 Mhz, which includes our VHF marine band. Most boaters will get
the little white Shakespeare VHF power and SWR meter from Waste Marine
or some other overpricing boat shop so that's what I'll use for my
example.

These little passive SWR meters use the RF power of your radio to
power the meter and require no batteries or power source. One guy I
know got no reading and through the meter had dead batteries in it.
There aren't any. His transmitter power amp was kaput....no output.

THE CONTROLS.

The controls on it are quite simple. There's a switch that switches
from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
jack plugged into a 50 ohm dummy load like the guys at the factory did
to calibrate it. Depending on the position of the meter in the line
of a defective antenna system, it might read way low or it might peg
on 1 watt. Consider it fairly accurate if the SWR of the antenna is
quite low (below 1.5 to 1)

So, What's SWR??.....

SWR (pronounced as three letters, unless you're on CB where it's
called "swur" for some reason noone knows) means Standing Wave Ratio.
The keyword there is RATIO, a measurement of the peak voltage found on
the transmission line in one place, compared to the minimum (trough?)
voltage found 1/4 wavelength from that peak in either direction.
These peaks and valleys are caused by reflections of an imperfect or
off-tuned antenna, bad connectors, kinked transmission lines bent too
sharply and a lot of just poor luck. You can watch these waves out by
the seawall. If you toss a rock into the water (transmitter) it
creates waves that expand out in all directions. When the wave
bounces off the seawall, watch what happens. The wave coming in from
the stone bounce off the REFLECTIVE seawall and go BACK towards the
transmitter, a "reflected power" that wasn't absorbed by the wall. As
the reflected waves pass through the incoming waves that haven't
reflected, yet, notice how there is a wave that doesn't move.....a
Standing Wave that has PEAK positions that stand still a set distance
from TROUGH positions, that also stand still.

The same exact thing is going on in your antenna system, every time
you press that button. In electronics, there are two simple devices
that STORE electrons....capacitors that charge (electrostatically) and
inductors that store energy (magnetically). If you doubt this, go out
and pull the spark plug wire off a running Seagull outboard to test
this theory....we'll wait. Ah, I see you're back? Why do you look so
"shocked"? Did it work?

A perfect RF transmission system perfectly transfers the power from
the transmitter to the perfect antenna, which radiates all the power
the transmitter put out into the air, blasting all the recievers with
your fantastic signal so they can hear your pleas for help. These
systems do not exist. The antenna is never tuned to your channel,
only close to your channel (we hope) and the transmission line is that
cheap white crap from Wasted Marine or RatShack, not rigid coaxial
line used by broadcast stations, made to exacting standards. To keep
it short, the line and antenna have "reactance", like that wall. And
it's that reactance (inductance and capacitance) that cause anomolies
that make reflections, like that wall.

What can we do? How can we measure how bad it is?...............

Most marine antennas are sealed up and "pretuned" for open areas. Not
much we can do to "tune" them to the middle of the band. I like old
Metz antennas, made by an old ham company, just because I can trim
that element for best results. It's tunable. That fishing pole of a
fiberglass antenna is actually a little, specially bent wire embedded
inside fiberglass to keep it straight (and disintegrate reliably in
sunshine so you can replace it, often). "Pruning" the tunable antenna
requires us to measure SWR at different frequencies so we can center
its curve up on the band we want for best results.

What "curve"??

An antenna "resonates", where the inductance balances out the
capacitance and acts like a radiating resistive load, over a fairly
large range of frequencies, not just one. Lucky for us.....it can be
made to pass channel 1 and channel 72, fairly reliably, without
retuning like you have to do to change channels on the HF SSB antenna.
The curve looks kinda like this:
| * *
SWR| * *
| * *
| *
Frequency

If we center the best (lowest) SWR up in the middle of the band, it
will have an acceptable SWR (low) on channels on the bottom and top we
want, and are allowed to use. Part of the testing, we will test
different channels across the marine band to get an idea of what YOUR
plot would look like.

So, how do we measure SWR??.............

For the little meter to measure the antenna, it has to be located
INLINE with the RF power, between the transmitter and antenna.
IDEALLY, we'd like to adjust the antenna with the SWR meter located
between the transmission line, antenna end, and the antenna's coax
connector. Obviously, sometimes, this is not practical for a simple
test. However, the further you are from the antenna, back down the
transmission line, the less the reading is about the antenna SWR and
the more the reading is about the cable losing the signal (attenuation
and leakage) and the reactivity of the cable, itself. If we measure
the SWR at the antenna end, the SWR we measure is only about the
antenna. If we measure it where it's easy, at the radio, the reading
is about the antenna AND the cable, so you can't tell which is at
fault if it sucks.

OK, let's assume you're like me, hate heights, weigh too much to haul
up on a winch with less than 6 strong arms on a winch handle and the
bos'n's chair might not like the load, anyways. So, we'll measure the
antenna at the radio end, at least until we find it's all screwed up.
Disconnect the antenna from the radio, with the radio off so you don't
inadvertently transmit into an open which might do harm to the
transmitter.

Now you need a "coax jumper" that didn't come with the meter. Radio
Shack has them, so get one that's just long enough to hook the meter's
RADIO port to the radio so we can still read it and switch the
controls. If you'd like to MOUNT the meter on your panel, buy two
right-angle UHF 90 degree adapters so we can mount the meter on the
front of the panel and the L-shaped connectors will go back through
the panel to connect the cables to. That would let you see power
output every time you keyed the VHF so you'd be SURE it was
transmitting, instead of calling out for a radio check so often. I
leave them in SWR to watch the antenna, here.

Hook the antenna to the antenna jack and the jumper between the Radio
jack and the radio. Turn on the radio and tune it to a commercial
channel not monitored by the DEA or USCG around 40-something. Put the
meter's little switch in the REFERENCE or SET position and turn the
set control all the way to the left, to keep from pegging the meter.
Test at FULL POWER so you can see if something up there is arcing at
FULL POWER (the meter jumps up in SWR if it is).

Key the transmitter and don't talk into the mic. Turn up the SET level
"volume" control until the meter reads FULL SCALE, all the way to the
SET mark. This sets the reference level of the meter to the power
coming out of the radio "under these conditions". Once set to full
scale, flip the switch to SWR and pray it drops all the way to 1 on
the SWR scale (no reflected power) indicating I was a liar and there
IS a perfect antenna system.....Read the pseudo-accurate meter SWR
scale. 1 is the left edge (1:1 standing waves - there aren't any
standing waves because the antenna is perfect). The next mark up is
probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
mic before the cops start looking for you.

What does this mean??

Here's the relative power levels of the major points.

1.0 SWR....no reflected power....all 25W is going out on the air
1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
out and noone notices anything because you couldn't measure 4% out of
the lab.
2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
goes out on the air and STILL noone notices anything unless they are
magicians.
3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
goes out on the air. Someone comparing this antenna with your perfect
antenna just notices a little movement in his S-meter on the other end
if you're weak. 3.0 and above is considered "bad SWR" and something
needs to be fixed.



CB myths........
1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
they get this from? ANTENNA MANUFACTURERS selling new antennas,
that's where. They made millions from this myth. Wanna see a real
broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
http://www.wzpxtv.com/wzpxtransmitter.htm
This a real readout of a powerful +megawatt TV transmitter from WZPX
on Channel 44 (with a nice new digital TV transmitter, too!) The
software company puts it on the net. SWR tonight on the
beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
really high at these power levels. On your boat, it's not. You don't
have thousands of watts coming back down the pipes at you!

Ok, now always turn the SET control back to the left before unhooking
the meter or changing channels. Do it now.....

Ok, make the same measurements on a few channels (not 16, 22A please)
across the marine band. Record your SWR results and make a crude
chart of them plotting SWR measured against channel (frequency) number
like I did above.

Is the lowest SWR near the middle of the channel numbers? No? Does
the curve at least have a low point (dip) inside the marine band?
Yes, but the dip is around Channel 3 and SWR is much higher at Channel
72 (why they could hear you on 16 but not 72 way off). The antenna is
tuned too LOW. If it's tunable, we need to shorten the element to
raise the resonant frequency. If 1 is high SWR and 72 is low, we need
to lengthen the antenna element. Ideal is a curve with its low point
somewhere in the middle of the band with less than 2:1 SWR on any
channel. The curve shows you where the antenna tuning is and how
broadbanded (how many channels will it radiate well).

If you measure this curve up at the antenna before all that cable
attenuates the SWR reading, it will simply be much more pronounced
because the cable attenuates power up as well as it does power down
the mast....making our reading weaker by a bit. AS you can see,
tuning an antenna ISN'T rocket science. If the channels you use are
all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
CABLE OR THE MEASUREMENT, because every antenna has a curve.

Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
trim the antenna the way it shows in the instructions......

You all should be able to measure SWR just fine with the little
meters, now, and have a vague idea of what it means.

Please leave the classroom quietly so's not to wake the four students
in the back row we lost. (Class quietly leaves, instructor slips out
and puts lights out with them still asleep. One once slept right
through lunch....(c;)



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

In article ,
"Doug Dotson" wrote:

I prefer a reflected power meter. Much more inruitive than
an SWR meter. Converting from RP to SWR is a simple formula
as well.

Doug, k3qt
s/v Callista

Nothing like a good Bird Wattmeter, fresh out of the Cal Shop,
to see what's going on in an Antenna System.

Bruce in alaska
--
add a 2 before @

How to use a simple SWR meter and what it means to your VHF
 

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


/Marcus

--
Marcus AAkesson
Gothenburg Callsigns: SM6XFN & SB4779
Sweden
Keep the world clean - no HTML in news or mail !

How to use a simple SWR meter and what it means to your VHF
 

GPL, open source. Feel free....(c;



On Wed, 12 Nov 2003 14:13:39 GMT, "Charlie J"
wrote:

Thank you Professor; you explained this operation far more succinctly than I
have. Consider yourself plagarized the next time I am explaining SWR to a
client ;-)

73-
Charlie
JTB Marine Service




Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

Good explanation, thanks. Questions:

1) You suggest the possibility of leaving the meter in the line permanently.
Doesn't the impedance bump of a PL-259 speak against that?

Another myth. The impedance bump might mean something on 5.4 Ghz, but
this is VHF-FM. It makes no difference, whatsoever. Put this myth in
the same class as the CBers working hard to correct that 1.1 SWR...(c;

2) Since the meter is not type accepted, is leaving it in permanently
technically an FCC violation?

No, it's not. It's not an amplifier.......

3) I went to
http://www.wzpxtv.com/wzpxtransmitter.htm
and saw a bunch of readouts. The readout labeled "VSWR" (which I think is
the same thing) was reading 0.80 or 0.70.

Hmm.....SWR doesn't come in levels under 1.0, which is perfect. Might
have been reflected power in kilowatts at a TV station.

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?

Belden is the best cable made. It's fine. My tongue-in-cheek comment
was about buying only WHITE "marine" coax from Waste Marine. Price
has nothing to do with cable quality, especially on boats.

An unrelated myth is about cable quality used on cable internet
connections. I know someone who was about to rip out all his house
cabling because it was RG-59 that was just fine. The cable company is
hosed with signal intrusion because they refuse to fix the problem, so
tell the customers it's their cable that's the problem. To dispel
this nonsense, I invited him to come to see how great my cable
internet was and look over my cable installation to get great ideas.
He took the bait and made an appointment to come the next day.

I disconnected my cable from the modem and hid it by pushing it back
into the floor. I took 50' of brown zipcord I use to put up speakers
in churches and ran a length from the cable company box out back, down
the side of the house, through the window next to my desk and up to a
wire to F connector adapter on the back of the modem with screw banana
jacks on it...same as outside after this "conversion".

He almost died when he saw the installation just hangin'
there......and working perfectly on the screen. I was watching Saudi
TV at 300kbps when he came through the door.

He didn't rewire the house. We found a cable guy to fix the street
feed two houses down, the one with the open shield.....

I put the coax back on my modem so none of the neighbors would be
seeing double on channels 2, 4, 5, 7, 24 and 36 from the zipcord...(c;



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

Fur Shur!

"Bruce in Alaska" wrote in message
...
In article ,
"Doug Dotson" wrote:

I prefer a reflected power meter. Much more inruitive than
an SWR meter. Converting from RP to SWR is a simple formula
as well.

Doug, k3qt
s/v Callista

Nothing like a good Bird Wattmeter, fresh out of the Cal Shop,
to see what's going on in an Antenna System.

Bruce in alaska
--
add a 2 before @

How to use a simple SWR meter and what it means to your VHF
 

Marcus AAkesson wrote:

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


Check out http://www.therfc.com/attenrat.htm

Common RG-58A (the white crap) looses 7.4dB/100 ft at 200MHz. That's
over half your signal used to heat the coax! RG-8X (mini-RG8 - the other
white crap) is almost as bad at 5.4 dB/100'. Belden 9913 is excellent at
only 1.8dB/100. RG-214 has 3.3dB loss/100' but as Marcus suggests may
have better corrosion resistance. Of course if money, size and weight
are unimportant there's LDF5 (c:

How to use a simple SWR meter and what it means to your VHF
 

Thanks to Marcus for suggesting RG214 and Vito for the numbers. On
Swee****er it was about 110 feet from radio to antenna (82' in the mast,
plus radio to mast), so I worried about losses. The bare copper solid #10
AWG center conductor of 9913 won't corrode much, and the shield is tinned,
so it won't corrode much either.

On Fintry, it's only about 25' from radios to antennas, and the antenna end
is much closer to the sea, so I'll probably use RG214 unless someone has a
better idea. Besides, putting 259s on that #10 wire is a pain.


--
Jim Woodward
www.mvFintry.com


..
"Vito" wrote in message
...
Marcus AAkesson wrote:

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable?
I
used Belden 9913 (solid center conductor) on Swee****er. Is that still
a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


Check out http://www.therfc.com/attenrat.htm

Common RG-58A (the white crap) looses 7.4dB/100 ft at 200MHz. That's
over half your signal used to heat the coax! RG-8X (mini-RG8 - the other
white crap) is almost as bad at 5.4 dB/100'. Belden 9913 is excellent at
only 1.8dB/100. RG-214 has 3.3dB loss/100' but as Marcus suggests may
have better corrosion resistance. Of course if money, size and weight
are unimportant there's LDF5 (c:

How to use a simple SWR meter and what it means to your VHF
 

In article ,
"Jim Woodward" jameslwoodward at attbi dot com wrote:

Good explanation, thanks. Questions:

1) You suggest the possibility of leaving the meter in the line permanently.
Doesn't the impedance bump of a PL-259 speak against that?

2) Since the meter is not type accepted, is leaving it in permanently
technically an FCC violation?

3) I went to
http://www.wzpxtv.com/wzpxtransmitter.htm
and saw a bunch of readouts. The readout labeled "VSWR" (which I think is
the same thing) was reading 0.80 or 0.70.

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?



--
Jim Woodward
www.mvFintry.com

1. PL-259's do leave an impedance bump in the line, that's true, but the
significance of that is questionable, as to the effect on Radio
Operation.

2. Only Active Transmitters and Receivers are Type Accepted by the FCC.
Passive components like coax, antennas, power supplys, ect are up to
the licensee to deal with and not subject to FCC as they aren't addressed
in Part 80.

3. Been using 9913 since I did some of the original enviormental
testing for Beldon. I use it darn near everywhere. Just remeber that it
has a Bend Radius of about 8" and if you kink it, you just trashed it.
Connectors for 9913 are a bit different to install, and AMP had to
come out with a new shinch design for their N Type Connectors for 9913.
also if you get a split in the jacket, water can be a real problem
in 9913.

Bruce in alaska
--
add a 2 before @

How to use a simple SWR meter and what it means to your VHF
 

Larry

That's the best description I've seen, brilliant.
Regards,
Brian

"Larry W4CSC" wrote in message
...
I've seen many posters talk about antennas and know lots of boaters
with antenna troubles and no clue how to see how it's doing, way up
there, so thought I'd stick my neck into the guillotine and give some
basic instructions on what an SWR meter is, what it does, and what it
means after you learn how to use it. This will be all about VHF
marine band, but is the same for any frequency the meter is made for.

FIRST, let me say not all SWR meters are suitable for VHF marine band
use. The reason for this has to do with the directional coupler, the
part that senses power going this way and power going that way built
into your meter. A CB SWR meter is NOT suitable for VHF work. VHF is
out of its design range and its directional coupler is too long. Put
using a CB SWR meter out of your mind. It's not a good reading. A
ham radio VHF SWR meter IS acceptable as its range is usually from 140
to 170 Mhz, which includes our VHF marine band. Most boaters will get
the little white Shakespeare VHF power and SWR meter from Waste Marine
or some other overpricing boat shop so that's what I'll use for my
example.

These little passive SWR meters use the RF power of your radio to
power the meter and require no batteries or power source. One guy I
know got no reading and through the meter had dead batteries in it.
There aren't any. His transmitter power amp was kaput....no output.

THE CONTROLS.

The controls on it are quite simple. There's a switch that switches
from POWER OUTPUT to REFERENCE (SETUP) to SWR, a 3-position slide
switch. The POWER OUTPUT meter is useless unless you have the ANTENNA
jack plugged into a 50 ohm dummy load like the guys at the factory did
to calibrate it. Depending on the position of the meter in the line
of a defective antenna system, it might read way low or it might peg
on 1 watt. Consider it fairly accurate if the SWR of the antenna is
quite low (below 1.5 to 1)

So, What's SWR??.....

SWR (pronounced as three letters, unless you're on CB where it's
called "swur" for some reason noone knows) means Standing Wave Ratio.
The keyword there is RATIO, a measurement of the peak voltage found on
the transmission line in one place, compared to the minimum (trough?)
voltage found 1/4 wavelength from that peak in either direction.
These peaks and valleys are caused by reflections of an imperfect or
off-tuned antenna, bad connectors, kinked transmission lines bent too
sharply and a lot of just poor luck. You can watch these waves out by
the seawall. If you toss a rock into the water (transmitter) it
creates waves that expand out in all directions. When the wave
bounces off the seawall, watch what happens. The wave coming in from
the stone bounce off the REFLECTIVE seawall and go BACK towards the
transmitter, a "reflected power" that wasn't absorbed by the wall. As
the reflected waves pass through the incoming waves that haven't
reflected, yet, notice how there is a wave that doesn't move.....a
Standing Wave that has PEAK positions that stand still a set distance
from TROUGH positions, that also stand still.

The same exact thing is going on in your antenna system, every time
you press that button. In electronics, there are two simple devices
that STORE electrons....capacitors that charge (electrostatically) and
inductors that store energy (magnetically). If you doubt this, go out
and pull the spark plug wire off a running Seagull outboard to test
this theory....we'll wait. Ah, I see you're back? Why do you look so
"shocked"? Did it work?

A perfect RF transmission system perfectly transfers the power from
the transmitter to the perfect antenna, which radiates all the power
the transmitter put out into the air, blasting all the recievers with
your fantastic signal so they can hear your pleas for help. These
systems do not exist. The antenna is never tuned to your channel,
only close to your channel (we hope) and the transmission line is that
cheap white crap from Wasted Marine or RatShack, not rigid coaxial
line used by broadcast stations, made to exacting standards. To keep
it short, the line and antenna have "reactance", like that wall. And
it's that reactance (inductance and capacitance) that cause anomolies
that make reflections, like that wall.

What can we do? How can we measure how bad it is?...............

Most marine antennas are sealed up and "pretuned" for open areas. Not
much we can do to "tune" them to the middle of the band. I like old
Metz antennas, made by an old ham company, just because I can trim
that element for best results. It's tunable. That fishing pole of a
fiberglass antenna is actually a little, specially bent wire embedded
inside fiberglass to keep it straight (and disintegrate reliably in
sunshine so you can replace it, often). "Pruning" the tunable antenna
requires us to measure SWR at different frequencies so we can center
its curve up on the band we want for best results.

What "curve"??

An antenna "resonates", where the inductance balances out the
capacitance and acts like a radiating resistive load, over a fairly
large range of frequencies, not just one. Lucky for us.....it can be
made to pass channel 1 and channel 72, fairly reliably, without
retuning like you have to do to change channels on the HF SSB antenna.
The curve looks kinda like this:
| * *
SWR| * *
| * *
| *
Frequency

If we center the best (lowest) SWR up in the middle of the band, it
will have an acceptable SWR (low) on channels on the bottom and top we
want, and are allowed to use. Part of the testing, we will test
different channels across the marine band to get an idea of what YOUR
plot would look like.

So, how do we measure SWR??.............

For the little meter to measure the antenna, it has to be located
INLINE with the RF power, between the transmitter and antenna.
IDEALLY, we'd like to adjust the antenna with the SWR meter located
between the transmission line, antenna end, and the antenna's coax
connector. Obviously, sometimes, this is not practical for a simple
test. However, the further you are from the antenna, back down the
transmission line, the less the reading is about the antenna SWR and
the more the reading is about the cable losing the signal (attenuation
and leakage) and the reactivity of the cable, itself. If we measure
the SWR at the antenna end, the SWR we measure is only about the
antenna. If we measure it where it's easy, at the radio, the reading
is about the antenna AND the cable, so you can't tell which is at
fault if it sucks.

OK, let's assume you're like me, hate heights, weigh too much to haul
up on a winch with less than 6 strong arms on a winch handle and the
bos'n's chair might not like the load, anyways. So, we'll measure the
antenna at the radio end, at least until we find it's all screwed up.
Disconnect the antenna from the radio, with the radio off so you don't
inadvertently transmit into an open which might do harm to the
transmitter.

Now you need a "coax jumper" that didn't come with the meter. Radio
Shack has them, so get one that's just long enough to hook the meter's
RADIO port to the radio so we can still read it and switch the
controls. If you'd like to MOUNT the meter on your panel, buy two
right-angle UHF 90 degree adapters so we can mount the meter on the
front of the panel and the L-shaped connectors will go back through
the panel to connect the cables to. That would let you see power
output every time you keyed the VHF so you'd be SURE it was
transmitting, instead of calling out for a radio check so often. I
leave them in SWR to watch the antenna, here.

Hook the antenna to the antenna jack and the jumper between the Radio
jack and the radio. Turn on the radio and tune it to a commercial
channel not monitored by the DEA or USCG around 40-something. Put the
meter's little switch in the REFERENCE or SET position and turn the
set control all the way to the left, to keep from pegging the meter.
Test at FULL POWER so you can see if something up there is arcing at
FULL POWER (the meter jumps up in SWR if it is).

Key the transmitter and don't talk into the mic. Turn up the SET level
"volume" control until the meter reads FULL SCALE, all the way to the
SET mark. This sets the reference level of the meter to the power
coming out of the radio "under these conditions". Once set to full
scale, flip the switch to SWR and pray it drops all the way to 1 on
the SWR scale (no reflected power) indicating I was a liar and there
IS a perfect antenna system.....Read the pseudo-accurate meter SWR
scale. 1 is the left edge (1:1 standing waves - there aren't any
standing waves because the antenna is perfect). The next mark up is
probably 1.5 with hashmarkes for 1.4, 1.3, 1.2, 1.1, which is silly.
Then it's 2:1 then the middle of the meter is 3:1 SWR and there's no
marks higher because 3:1 is BAD, BAD, BAD....way too high. Unkey the
mic before the cops start looking for you.

What does this mean??

Here's the relative power levels of the major points.

1.0 SWR....no reflected power....all 25W is going out on the air
1.5 SWR.....4% reflected power....1 watt is reflected back, 24W goes
out and noone notices anything because you couldn't measure 4% out of
the lab.
2.0 SWR......10% reflected power...2.5W is reflected back and 22.5 W
goes out on the air and STILL noone notices anything unless they are
magicians.
3.0 SWR......25% reflected power....6.25W is reflected back and 18.75W
goes out on the air. Someone comparing this antenna with your perfect
antenna just notices a little movement in his S-meter on the other end
if you're weak. 3.0 and above is considered "bad SWR" and something
needs to be fixed.



CB myths........
1.01 SWR is good. 1.1 SWR is a disaster. What nonsense. Where do
they get this from? ANTENNA MANUFACTURERS selling new antennas,
that's where. They made millions from this myth. Wanna see a real
broadcast TV station's huge UHF antenna SWR LIVE on the net? Look at:
http://www.wzpxtv.com/wzpxtransmitter.htm
This a real readout of a powerful +megawatt TV transmitter from WZPX
on Channel 44 (with a nice new digital TV transmitter, too!) The
software company puts it on the net. SWR tonight on the
beast-on-the-mountain is 1.3:1 but I've seen it read 1.8:1 which is
really high at these power levels. On your boat, it's not. You don't
have thousands of watts coming back down the pipes at you!

Ok, now always turn the SET control back to the left before unhooking
the meter or changing channels. Do it now.....

Ok, make the same measurements on a few channels (not 16, 22A please)
across the marine band. Record your SWR results and make a crude
chart of them plotting SWR measured against channel (frequency) number
like I did above.

Is the lowest SWR near the middle of the channel numbers? No? Does
the curve at least have a low point (dip) inside the marine band?
Yes, but the dip is around Channel 3 and SWR is much higher at Channel
72 (why they could hear you on 16 but not 72 way off). The antenna is
tuned too LOW. If it's tunable, we need to shorten the element to
raise the resonant frequency. If 1 is high SWR and 72 is low, we need
to lengthen the antenna element. Ideal is a curve with its low point
somewhere in the middle of the band with less than 2:1 SWR on any
channel. The curve shows you where the antenna tuning is and how
broadbanded (how many channels will it radiate well).

If you measure this curve up at the antenna before all that cable
attenuates the SWR reading, it will simply be much more pronounced
because the cable attenuates power up as well as it does power down
the mast....making our reading weaker by a bit. AS you can see,
tuning an antenna ISN'T rocket science. If the channels you use are
all less than 2:1, it's fine. If they're less than 1.5:1, it's great.
If they're all really low....SOMETHING IS WRONG WITH THE ANTENNA, THE
CABLE OR THE MEASUREMENT, because every antenna has a curve.

Ok, we'll now haul a victim....er, ah, volunteer....up the mast to
trim the antenna the way it shows in the instructions......

You all should be able to measure SWR just fine with the little
meters, now, and have a vague idea of what it means.

Please leave the classroom quietly so's not to wake the four students
in the back row we lost. (Class quietly leaves, instructor slips out
and puts lights out with them still asleep. One once slept right
through lunch....(c;)



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

One thing to consider and weigh in is the actual difference to the
receiver you're talking to...on-the-air...where it matters. Look at
any receiver or transceiver with a pseudo-calibrated S-meter. Notice
the DB scale above S-9. See how the marks are 10 dB apart? This is
also true down the scale.

So, before you all go hauling 7/8" hardline up the mast and boring
huge holes in the fiberglass to route it, the difference on-the-air,
where it counts is that instead of your signal being S-9 on somebody's
meter with 7/8" hardline and $200 connectors, you're RG-58 signal will
only be S-8.5 and noone will notice any difference....(c;

More CB myths. Most boats only have a 25-50' coax run. What I DO
recommend is a good Belden foil shielded cable, which will require
proper crimp connectors to make it work, not PL-259's from WalMart.
The 100% foil shield will keep locally generated noise OUT of the
cable on receive on its way from the antenna to your sensitive
receiver. You won't have to listen to the cheap straight plugs marine
engine manufacturers love to put in outboard and inboard motors,
instead of the resistor plugs they should be using. The foil coax
will also get a little more signal to the antenna on transmit, but
"big deal"....(c;

On Thu, 13 Nov 2003 09:33:27 -0500, Vito wrote:

Marcus AAkesson wrote:

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


Check out http://www.therfc.com/attenrat.htm

Common RG-58A (the white crap) looses 7.4dB/100 ft at 200MHz. That's
over half your signal used to heat the coax! RG-8X (mini-RG8 - the other
white crap) is almost as bad at 5.4 dB/100'. Belden 9913 is excellent at
only 1.8dB/100. RG-214 has 3.3dB loss/100' but as Marcus suggests may
have better corrosion resistance. Of course if money, size and weight
are unimportant there's LDF5 (c:


Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

On Fri, 14 Nov 2003 11:47:11 -0000, "Brian Runyard"
wrote:

Larry

That's the best description I've seen, brilliant.
Regards,
Brian

Oh, p'shaw.....T'weren't nuthin....(c;....(blush)

I used to teach electronics 8 hours a day for 10 years.... After
you've gone over a subject 20 times, you get so you know it fairly
well! If you want to learn anything about any subject, get a job
teaching it to a bunch of teenagers trying to nail you to the
blackboard with real smart questions and you'll learn it QUICK!

"......but you said last week, and I quote....." You can hear that
nail gun compressor warmin' up in the back of the classroom...(c;

I'd much rather have the nail gun guys keeping me hopping than those
ones sleeping in the back of the side rows. We used to all sneak out
really quiet on them, shutting off the lights as quietly as
possible....leaving them sleeping in an empty, dark classroom with no
windows and no idea what time it is. Very effective in keeping them
awake..hee hee.

Thanks for your comment. Tomorrow, someone can come explain how the
hand-pumped, marine toilet functions and what it means when it refuses
to flush and makes that gurgling sound, instead. We'd ALL like to get
a little instruction on that piece of engineering!



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

All true, in most cases. Maybe even here. My thinking, however, was that
Swee****er's tall stick (82 feet) did two things -- it made the lead
longer, so lossiness was more important -- and it put the antenna higher, so
we actually might be at the point where line of sight was less important
than signal strength, both going and coming.

We regularly talked to boats that were thirty to fifty miles away. Maybe
this is routine -- I don't know -- but I'd like to think that attention to
detail and the 9913 helped.


--
Jim Woodward
www.mvFintry.com


..

"Larry W4CSC" wrote in message
...
One thing to consider and weigh in is the actual difference to the
receiver you're talking to...on-the-air...where it matters. Look at
any receiver or transceiver with a pseudo-calibrated S-meter. Notice
the DB scale above S-9. See how the marks are 10 dB apart? This is
also true down the scale.

So, before you all go hauling 7/8" hardline up the mast and boring
huge holes in the fiberglass to route it, the difference on-the-air,
where it counts is that instead of your signal being S-9 on somebody's
meter with 7/8" hardline and $200 connectors, you're RG-58 signal will
only be S-8.5 and noone will notice any difference....(c;

More CB myths. Most boats only have a 25-50' coax run. What I DO
recommend is a good Belden foil shielded cable, which will require
proper crimp connectors to make it work, not PL-259's from WalMart.
The 100% foil shield will keep locally generated noise OUT of the
cable on receive on its way from the antenna to your sensitive
receiver. You won't have to listen to the cheap straight plugs marine
engine manufacturers love to put in outboard and inboard motors,
instead of the resistor plugs they should be using. The foil coax
will also get a little more signal to the antenna on transmit, but
"big deal"....(c;

On Thu, 13 Nov 2003 09:33:27 -0500, Vito wrote:

Marcus AAkesson wrote:

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable?
I
used Belden 9913 (solid center conductor) on Swee****er. Is that
still a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


Check out http://www.therfc.com/attenrat.htm

Common RG-58A (the white crap) looses 7.4dB/100 ft at 200MHz. That's
over half your signal used to heat the coax! RG-8X (mini-RG8 - the other
white crap) is almost as bad at 5.4 dB/100'. Belden 9913 is excellent at
only 1.8dB/100. RG-214 has 3.3dB loss/100' but as Marcus suggests may
have better corrosion resistance. Of course if money, size and weight
are unimportant there's LDF5 (c:


Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

"Larry W4CSC" wrote in message
...

SNIP

Thanks for your comment. Tomorrow, someone can come explain how the
hand-pumped, marine toilet functions and what it means when it refuses
to flush and makes that gurgling sound, instead. We'd ALL like to get
a little instruction on that piece of engineering!



Aw, sheeeet....


--
Jim Woodward
www.mvFintry.com


..

How to use a simple SWR meter and what it means to your VHF
 

Any loss in cable is FAR amplified by ALTITUDE on VHF. It's why WCSC
has a 2000' tower. From 2000', a rubber duck antenna on a 1 watt
walkie talkie has a range of over 100 miles. Line of sight is what's
important. The only reason you need the power is to overcome noise
and the damned marinas docking boats from a 70' tower with a 9 dB
antenna running 25 watts to get to the end of the dock. Why the FCC
doesn't restrict marinas to 1W and 10' AGL has always been a mystery
to me. They're NOT part of any rescue party, manned by teenage girls.



On Fri, 14 Nov 2003 10:27:00 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

All true, in most cases. Maybe even here. My thinking, however, was that
Swee****er's tall stick (82 feet) did two things -- it made the lead
longer, so lossiness was more important -- and it put the antenna higher, so
we actually might be at the point where line of sight was less important
than signal strength, both going and coming.

We regularly talked to boats that were thirty to fifty miles away. Maybe
this is routine -- I don't know -- but I'd like to think that attention to
detail and the 9913 helped.


--
Jim Woodward
www.mvFintry.com


.

"Larry W4CSC" wrote in message
...
One thing to consider and weigh in is the actual difference to the
receiver you're talking to...on-the-air...where it matters. Look at
any receiver or transceiver with a pseudo-calibrated S-meter. Notice
the DB scale above S-9. See how the marks are 10 dB apart? This is
also true down the scale.

So, before you all go hauling 7/8" hardline up the mast and boring
huge holes in the fiberglass to route it, the difference on-the-air,
where it counts is that instead of your signal being S-9 on somebody's
meter with 7/8" hardline and $200 connectors, you're RG-58 signal will
only be S-8.5 and noone will notice any difference....(c;

More CB myths. Most boats only have a 25-50' coax run. What I DO
recommend is a good Belden foil shielded cable, which will require
proper crimp connectors to make it work, not PL-259's from WalMart.
The 100% foil shield will keep locally generated noise OUT of the
cable on receive on its way from the antenna to your sensitive
receiver. You won't have to listen to the cheap straight plugs marine
engine manufacturers love to put in outboard and inboard motors,
instead of the resistor plugs they should be using. The foil coax
will also get a little more signal to the antenna on transmit, but
"big deal"....(c;

On Thu, 13 Nov 2003 09:33:27 -0500, Vito wrote:

Marcus AAkesson wrote:

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable?
I
used Belden 9913 (solid center conductor) on Swee****er. Is that
still a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


Check out http://www.therfc.com/attenrat.htm

Common RG-58A (the white crap) looses 7.4dB/100 ft at 200MHz. That's
over half your signal used to heat the coax! RG-8X (mini-RG8 - the other
white crap) is almost as bad at 5.4 dB/100'. Belden 9913 is excellent at
only 1.8dB/100. RG-214 has 3.3dB loss/100' but as Marcus suggests may
have better corrosion resistance. Of course if money, size and weight
are unimportant there's LDF5 (c:


Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"





Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

In article ,
"Jim Woodward" jameslwoodward at attbi dot com wrote:

We regularly talked to boats that were thirty to fifty miles away. Maybe
this is routine -- I don't know -- but I'd like to think that attention to
detail and the 9913 helped.

Jim, Just a note on the above, Out in the North Pacific, the fishing
fleet, routinely talks 90 -110 miles with 25 Watts on Vhf Maine
Frequencies. The antennas are in the 50' to 80' range above the water.
Some of the Coast Stations report contacts out to 120 Miles, using
120 Ft towers, and the 50 Watts at the antenna connection rule in
Part 80.

Bruce in alaska
--
add a 2 before @

How to use a simple SWR meter and what it means to your VHF
 

Larry W4CSC wrote:

snipped


Good post Larry. For my two cents - I switched several years back from
Belden to Times Microwave cable for everything. Lower losses and
personal experiences has been much better weather resistance.

Mike KG4RRH


More CB myths. Most boats only have a 25-50' coax run. What I DO
recommend is a good Belden foil shielded cable, which will require
proper crimp connectors to make it work, not PL-259's from WalMart.
The 100% foil shield will keep locally generated noise OUT of the
cable on receive on its way from the antenna to your sensitive
receiver. You won't have to listen to the cheap straight plugs marine
engine manufacturers love to put in outboard and inboard motors,
instead of the resistor plugs they should be using. The foil coax
will also get a little more signal to the antenna on transmit, but
"big deal"....(c;

On Thu, 13 Nov 2003 09:33:27 -0500, Vito wrote:

Marcus AAkesson wrote:

On Wed, 12 Nov 2003 15:41:08 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

4) What do you like other than the cheap white crap for antenna cable? I
used Belden 9913 (solid center conductor) on Swee****er. Is that still a
good choice?

RG214 or similar which is silver plated Cu in both conductor and
shield. Raw copper will in time oxidize and deteriorate in the salty
environment. I have seen some really ugly cables after only 5-6 years.


Check out http://www.therfc.com/attenrat.htm

Common RG-58A (the white crap) looses 7.4dB/100 ft at 200MHz. That's
over half your signal used to heat the coax! RG-8X (mini-RG8 - the other
white crap) is almost as bad at 5.4 dB/100'. Belden 9913 is excellent at
only 1.8dB/100. RG-214 has 3.3dB loss/100' but as Marcus suggests may
have better corrosion resistance. Of course if money, size and weight
are unimportant there's LDF5 (c:

Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

In addition to the trusty old Bird 43, I love my MFJ-259B HF/VHF SWR
Analyzer. It allow me to check an antenna without transmitting. Those
expensive Shakespeare antennas with the cell phone, VHF high band filters,
etc., are frequently mistuned right out of the box. Checking them at the
shop by sweeping through the marine band for good SWR has saved me a lot of
time and frustration of installing a brand new antenna on a boat and then
finding out it is bad out of box. Another use of the MFJ is trying
different positions of an antenna to find a location where adjacent metal is
not causing problem. I used it to find the best compromise location on my
van motorhome for a 2 meter bumper mounted colinear antenna that the close
proximity of the van metal sides interfered with.
Doug K7ABX
"Bruce in Alaska" wrote in message
...
In article ,
"Doug Dotson" wrote:

I prefer a reflected power meter. Much more inruitive than
an SWR meter. Converting from RP to SWR is a simple formula
as well.

Doug, k3qt
s/v Callista

Nothing like a good Bird Wattmeter, fresh out of the Cal Shop,
to see what's going on in an Antenna System.

Bruce in alaska
--
add a 2 before @

How to use a simple SWR meter and what it means to your VHF
 

On Fri, 14 Nov 2003 14:48:06 -0500, Stilz wrote:



Good post Larry. For my two cents - I switched several years back from
Belden to Times Microwave cable for everything. Lower losses and
personal experiences has been much better weather resistance.

Mike KG4RRH

In the interest of accuracy and truthfulness, Lionheart's VHF radios
are running off US Navy RG-58A/U because I got a 1000' roll of it for
free from a friend who buys tons of surplus stuff. I mentioned to him
one day that I needed some RG-58 for the car and he just went around
to the storage building and said, "Is one enough? I got lots."

Free coax has no loss at all that I can measure, can you?....(c;



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

How to use a simple SWR meter and what it means to your VHF
 

"Larry W4CSC" wrote in message
...
snip

The only reason you need the power is to overcome noise
and the damned marinas docking boats from a 70' tower with a 9 dB
antenna running 25 watts to get to the end of the dock. Why the FCC
doesn't restrict marinas to 1W and 10' AGL has always been a mystery
to me. They're NOT part of any rescue party, manned by teenage girls.

Actually, don't the rules say that we all MUST use 1W when possible? Thus
the marinas are actually in violation if they're using 25 watts. Of course,
the FCC has better things to do than enforce its own rules.

And thanks to all for comments in this thread. So many decisions, so little
solid information available on subjects like this. While you guys don't
always agree, at least I get a spectrum of views from people who mostly
don't have a horse in the race.


--
Jim Woodward
www.mvFintry.com


..

How to use a simple SWR meter and what it means to your VHF
 

In article t,
"Doug K7ABX" wrote:

In addition to the trusty old Bird 43, I love my MFJ-259B HF/VHF SWR
Analyzer. It allow me to check an antenna without transmitting. Those
expensive Shakespeare antennas with the cell phone, VHF high band filters,
etc., are frequently mistuned right out of the box. Checking them at the
shop by sweeping through the marine band for good SWR has saved me a lot of
time and frustration of installing a brand new antenna on a boat and then
finding out it is bad out of box. Another use of the MFJ is trying
different positions of an antenna to find a location where adjacent metal is
not causing problem. I used it to find the best compromise location on my
van motorhome for a 2 meter bumper mounted colinear antenna that the close
proximity of the van metal sides interfered with.
Doug K7ABX

Yep, I use an Impedance Bridge on my Cushman CE50A1 for doing that job.
It is very nice to have all the right tools, to do the job.

Bruce in alaska
--
add a 2 before @

How to use a simple SWR meter and what it means to your VHF
 

I suppose that is a matter of judgement. 1 watt is pretty useless when you
are an hour away trying to secure a slip for the night. Trying to secure a
slip 10 minutes before arrival is inconsiderate and places the marina on
the spot and can leave one with few alternatives if they cannot accomodate
you. Try reducing your power to 1 watt everytime you are communicating with
a marina and see how life is?

I just have to ask what the thinly vailed insult has to do with anything? I
think
Larry's explanation of SWR was quite valuable and others who chimed in
had valuable contributions as well. Certainly more useful than the Battery
Water
thread :)

Doug

"Jim Woodward" jameslwoodward at attbi dot com wrote in message
...
"Larry W4CSC" wrote in message
...
snip

The only reason you need the power is to overcome noise
and the damned marinas docking boats from a 70' tower with a 9 dB
antenna running 25 watts to get to the end of the dock. Why the FCC
doesn't restrict marinas to 1W and 10' AGL has always been a mystery
to me. They're NOT part of any rescue party, manned by teenage girls.

Actually, don't the rules say that we all MUST use 1W when possible? Thus
the marinas are actually in violation if they're using 25 watts. Of
course,
the FCC has better things to do than enforce its own rules.

And thanks to all for comments in this thread. So many decisions, so
little
solid information available on subjects like this. While you guys don't
always agree, at least I get a spectrum of views from people who mostly
don't have a horse in the race.


--
Jim Woodward
www.mvFintry.com


.

How to use a simple SWR meter and what it means to your VHF
 

Doug Dotson wrote:

I suppose that is a matter of judgement. 1 watt is pretty useless when you
are an hour away trying to secure a slip for the night. Trying to secure a
slip 10 minutes before arrival is inconsiderate and places the marina on
the spot and can leave one with few alternatives if they cannot accomodate
you. Try reducing your power to 1 watt everytime you are communicating with
a marina and see how life is?

I just have to ask what the thinly vailed insult has to do with anything? I
think
Larry's explanation of SWR was quite valuable and others who chimed in
had valuable contributions as well. Certainly more useful than the Battery
Water
thread :)

Doug



Good grief...that battery water thread has to be in the running for the
longest, dullest, most useless string of discombubulated thoughts ever
to be regurgitated on usenet.

Q: What kind of water do you use in your batteries?

A: Whatever's left in the Miller Lite cans.*





* I use AGM batteries, and drink the water.










--
Email sent to is never read.

How to use a simple SWR meter and what it means to your VHF
 

" * I use AGM batteries, and drink the water.

We do too, but remember that water will rust your plumbing.
Though is great for cooking, washing, or brushing teeth.

Leanne
S/V Fundy

How to use a simple SWR meter and what it means to your VHF
 

I've never seen a boat with metal plumbing. We use AGM as well and
avoid the battery water probem. Liquid electrolyte battery are obsolete
IMHO.

Doug

"Leanne" wrote in message
...

" * I use AGM batteries, and drink the water.

We do too, but remember that water will rust your plumbing.
Though is great for cooking, washing, or brushing teeth.

Leanne
S/V Fundy

How to use a simple SWR meter and what it means to your VHF
 

I guess you have the proverbial Iron Constitution :)

"Leanne" wrote in message
...
I've never seen a boat with metal plumbing.

Doug, I was referring to my internal plumbing and not the boat...

Leanne
S/V Fundy

How to use a simple SWR meter and what it means to your VHF
 

"Doug Dotson" wrote in message
...

snip

I just have to ask what the thinly vailed insult has to do with anything?
I think
Larry's explanation of SWR was quite valuable and others who chimed in
had valuable contributions as well.

snip
Doug

Doug:

If the comment above is aimed at me, we have a misunderstanding and I
apologize. To clarify the comment I made (see below):
1) Honest thanks to Larry and the rest of the posters in this thread. I
understand how much time it takes to write good posts such as Larry's
original explanation here (I sometmes wonder why any of us do it). While I'm
often a giver-of-advice in other newsgroups, on this one I'm usually a
taker; and when that happens I say "thank you".
2) Often there is little solid information in the marine world (or why would
we all be spending time here trading information)
3) You guys don't always agree -- that's OK, on some subjects I disagree
with myself.
4) We usually get a spectrum of views -- "different ships, different long
splices" -- with a spectrum we all get to decide which long splice we'll use
on our ship.
5) Asking antenna manufacturers or dealers, for example, what antenna to
use, is not always the best way to choose. Mostly, the people here don't
benefit directly from their advice. That's good. When they do benefit, it's
usually disclosed, which is also good.

I try very hard never to insult -- correct, yes; disagree with, often -- but
insult, never. If, however, I do, it won't be thinly veiled -- I'm very
direct, often to a fault.

Again, sorry for any misunderstanding.


--
Jim Woodward
www.mvFintry.com


..




The only reason you need the power is to overcome noise
and the damned marinas docking boats from a 70' tower with a 9 dB
antenna running 25 watts to get to the end of the dock. Why the FCC
doesn't restrict marinas to 1W and 10' AGL has always been a mystery
to me. They're NOT part of any rescue party, manned by teenage girls.

Actually, don't the rules say that we all MUST use 1W when possible?
Thus
the marinas are actually in violation if they're using 25 watts. Of
course,
the FCC has better things to do than enforce its own rules.

And thanks to all for comments in this thread. So many decisions, so
little
solid information available on subjects like this. While you guys don't
always agree, at least I get a spectrum of views from people who mostly
don't have a horse in the race.


--
Jim Woodward
www.mvFintry.com


.

How to use a simple SWR meter and what it means to your VHF
 

I agree with all of your points. It just didn't seem to be the
case of this thread. Nuff sed!

Doug

"Jim Woodward" jameslwoodward at attbi dot com wrote in message
...
"Doug Dotson" wrote in message
...

snip

I just have to ask what the thinly vailed insult has to do with
anything?
I think
Larry's explanation of SWR was quite valuable and others who chimed in
had valuable contributions as well.

snip
Doug

Doug:

If the comment above is aimed at me, we have a misunderstanding and I
apologize. To clarify the comment I made (see below):
1) Honest thanks to Larry and the rest of the posters in this thread. I
understand how much time it takes to write good posts such as Larry's
original explanation here (I sometmes wonder why any of us do it). While
I'm
often a giver-of-advice in other newsgroups, on this one I'm usually a
taker; and when that happens I say "thank you".
2) Often there is little solid information in the marine world (or why
would
we all be spending time here trading information)
3) You guys don't always agree -- that's OK, on some subjects I disagree
with myself.
4) We usually get a spectrum of views -- "different ships, different long
splices" -- with a spectrum we all get to decide which long splice we'll
use
on our ship.
5) Asking antenna manufacturers or dealers, for example, what antenna to
use, is not always the best way to choose. Mostly, the people here don't
benefit directly from their advice. That's good. When they do benefit,
it's
usually disclosed, which is also good.

I try very hard never to insult -- correct, yes; disagree with, often --
but
insult, never. If, however, I do, it won't be thinly veiled -- I'm very
direct, often to a fault.

Again, sorry for any misunderstanding.


--
Jim Woodward
www.mvFintry.com


.




The only reason you need the power is to overcome noise
and the damned marinas docking boats from a 70' tower with a 9 dB
antenna running 25 watts to get to the end of the dock. Why the FCC
doesn't restrict marinas to 1W and 10' AGL has always been a mystery
to me. They're NOT part of any rescue party, manned by teenage
girls.

Actually, don't the rules say that we all MUST use 1W when possible?
Thus
the marinas are actually in violation if they're using 25 watts. Of
course,
the FCC has better things to do than enforce its own rules.

And thanks to all for comments in this thread. So many decisions, so
little
solid information available on subjects like this. While you guys
don't
always agree, at least I get a spectrum of views from people who
mostly
don't have a horse in the race.


--
Jim Woodward
www.mvFintry.com


.

How to use a simple SWR meter and what it means to your VHF
 

SWR in itself is not necessarily bad. Power reflected back toward the
transmitter is not lost as a result of the reflection itself. When
that reflected power hits the transmitter it is re-reflected back up
to the antenna.

So a 3:1 swr with 6.25 watts of reflected power and 25 watts of
forward power, still delivers 25 watts to the antenna to be radiated.
That is of course when there is no feed line loss.


With feed line loss involved (as there always is) you will get a false
SWR reading. The more loss your cable has the better your SWR will
look.
This is because not only is there less power to reach the antenna that
is causing the reflection, but also there is less of the reflected
power that gets back to your SWR meter. It gets lost in the coax both
ways.

So if you have 3 db of line loss and your antenna has a 3:1 SWR, you
will only read it as about 1.4:1.

WHY:
With 3 db of line loss only 12.5 watts will make it to the antenna.
With a 3:1 SWR at that point 25% of the 12.5 watts (or 3.125 watts)
will be reflected back towards the SWR bridge. But the 3.125 watts
coming back down the cable will also undergo the 3 db of cable loss so
only .78 watts will show up as reflected power back at the SWR bridge.
That gets compared with the full 25 watts that the input of the SWR
bridge sees. The bridge will tell you that you have an SWR of only
about 1.4:1 when it is really 3:1!

Further, most SWR bridges are quite inaccurate at low readings. In the
area of 10 to 40%.

Even the revered Bird watt meter is not very accurate when reading on
the low end of the scale. It has a published accuracy of +- 5% of FULL
scale. Measuring a 25 watt radio, a 50 watt slug is normally used. 5%
of 50 watts is +-2.5 watts. Trying to read that 1.4:1 reflected power
level of .78 watts with a meter that has an error of +- greater than 3
times the level that you are trying to read leaves you guessing at
best!

Users of watt meters measuring reflected power often make the mistake
of seeing a few watts of reflected power and thinking things are "ok"
and not really calculating what they have, as the "reflected part is
rather low compared to the forward power". They equate it to an SWR
meter position comparison.

Bottom line is when using a watt meter on VHF to look at reflected
power, if the reflected indication is more than a division or two on
the meter you probably have to high an SWR.

With a short antenna cable, 20 or so feet, 1.5:1 SWR is about the
limit. With a longer cable, depending on its loss, The acceptable
limit may be much lower as seen above.

Some transmitters start shutting down their output at around 1.8:1
SWR.
So the problem with high SWR is not so much one of added loss as it is
a problem of the mismatch that the transmitter sees and reduces its
output power. Although with a high loss feed line you end up with less
of the reflected power to be re-reflected back up to the antenna.

Regards
Gary

How to use a simple SWR meter and what it means to your VHF
 

On Thu, 20 Nov 2003 03:50:41 GMT, Gary Schafer
wrote:

SWR in itself is not necessarily bad. Power reflected back toward the
transmitter is not lost as a result of the reflection itself. When
that reflected power hits the transmitter it is re-reflected back up
to the antenna.

Simply not true. The source impedance of the output power amplifier
is, ideally 50 ohms to match the cable. This impedance absorbs
reflected power, converting it into heat in its resistive component
which is lost. The output matching network of the transmitter is
tuned to make it look resistive. Almost nothing is reflected, again.

At 150W with a couple of watts reflected, it's a no-brainer. However,
if you are running a 50KW broadcast transmitter, reflected power
greatly increases the transmitter's output amp heating problems so
they are very careful with it. A 2:1 SWR means we have another 5000
watts of heat to cool off the finals, cooking them. The normally hot
finals simply cook themselves.

So a 3:1 swr with 6.25 watts of reflected power and 25 watts of
forward power, still delivers 25 watts to the antenna to be radiated.
That is of course when there is no feed line loss.

Too bad this isn't true. If the final amp were purely reactive, it
would be, but then there would be no match between the transmitter and
feed line to begin with so there'd be no power output if it were
purely reactive.

With feed line loss involved (as there always is) you will get a false
SWR reading. The more loss your cable has the better your SWR will
look.

Finally something that is true. SWR should be measured at the antenna
if the line is long and lossy. However, this isn't that important in
a boat with 50' of RG-58 at VHF.



73 de Larry W 4 C S C
h h o a
i a u r
s r t o
k l h l
e e i
y s n
t a
o
n

NNNN

How to use a simple SWR meter and what it means to your VHF
 

Simply not true?? You need to do some more reading Larry. A good
start would be Walter Maxwell's book "reflections". It is explained
there well. Even the later handbooks touch on the subject.

First, impedance does not "absorb any reflected power".
Reflected power on the antenna line DOES NOT go back into the final
amplifier and get dissipated. That is an old wives tale that is
probably older than all of us.

The reason for "being careful" on a high power transmitter with
reflected power is that the voltages can become very high due to the
high impedance's involved in the tank circuit. Also circulating
currents can become high in the matching components. Thus stressing
the circuit components. But no great amount of reflected power is
absorbed by anything.

Ever look at the color of the plates on a high power transmitter
working into a normal load verses a high SWR load? When tuned for the
same power level in both cases there is no difference in plate color.
If reflected power were being dissipated in the final plates they
would be hotter, indicated by a hotter color.

If you think that the tank coil in your 50 kw transmitter is going to
dissipate 5 kw in heat,, then watch it glow red. But we both know it
doesn't, right?

With solid state amplifiers there is the problem of transistors not
liking to work into complex impedance's. It causes them to draw very
high currents. Nothing to do with absorbing reflected power.

Have you ever used open wire feeders to an antenna? The SWR on the
feed line can be very high. It can be in the order of 15 or 20:1 on
the line depending on the antenna type and frequency being used. But
there is almost no additional loss on the line over the line being
1:1.
What do you think happens to all that reflected power on that feed
line?
Where do you think it gets dissipated? Hint, it all gets radiated.

Regards
Gary


On Thu, 20 Nov 2003 12:38:22 GMT, (Larry W4CSC) wrote:

On Thu, 20 Nov 2003 03:50:41 GMT, Gary Schafer
wrote:

SWR in itself is not necessarily bad. Power reflected back toward the
transmitter is not lost as a result of the reflection itself. When
that reflected power hits the transmitter it is re-reflected back up
to the antenna.

Simply not true. The source impedance of the output power amplifier
is, ideally 50 ohms to match the cable. This impedance absorbs
reflected power, converting it into heat in its resistive component
which is lost. The output matching network of the transmitter is
tuned to make it look resistive. Almost nothing is reflected, again.

At 150W with a couple of watts reflected, it's a no-brainer. However,
if you are running a 50KW broadcast transmitter, reflected power
greatly increases the transmitter's output amp heating problems so
they are very careful with it. A 2:1 SWR means we have another 5000
watts of heat to cool off the finals, cooking them. The normally hot
finals simply cook themselves.

So a 3:1 swr with 6.25 watts of reflected power and 25 watts of
forward power, still delivers 25 watts to the antenna to be radiated.
That is of course when there is no feed line loss.

Too bad this isn't true. If the final amp were purely reactive, it
would be, but then there would be no match between the transmitter and
feed line to begin with so there'd be no power output if it were
purely reactive.

With feed line loss involved (as there always is) you will get a false
SWR reading. The more loss your cable has the better your SWR will
look.

Finally something that is true. SWR should be measured at the antenna
if the line is long and lossy. However, this isn't that important in
a boat with 50' of RG-58 at VHF.



73 de Larry W 4 C S C
h h o a
i a u r
s r t o
k l h l
e e i
y s n
t a
o
n

NNNN

How to use a simple SWR meter and what it means to your VHF
 

"Gary Schafer" wrote in message
...
SWR in itself is not necessarily bad. Power reflected back toward the
transmitter is not lost as a result of the reflection itself. When
that reflected power hits the transmitter it is re-reflected back up
to the antenna.

And where it is reflected back into the cable again. And this continues
until the power is completely dissipated in by the losses in the path.

So a 3:1 swr with 6.25 watts of reflected power and 25 watts of
forward power, still delivers 25 watts to the antenna to be radiated.
That is of course when there is no feed line loss.

No. Power that is reflected the first time, will be reflected the secon time
it 'hits' the antenna. It wil NEVER be radiated.

Meindert

How to use a simple SWR meter and what it means to your VHF
 

Wouldn't phase be a problem? Hard to believe that a signal can
be reflected back from the antenna and then reflected back from the
transmitter to the antenna and will be in phase well enough to actually
do any good.

Doug, k3qt
s/v Callista

"Gary Schafer" wrote in message
...
SWR in itself is not necessarily bad. Power reflected back toward the
transmitter is not lost as a result of the reflection itself. When
that reflected power hits the transmitter it is re-reflected back up
to the antenna.

So a 3:1 swr with 6.25 watts of reflected power and 25 watts of
forward power, still delivers 25 watts to the antenna to be radiated.
That is of course when there is no feed line loss.


With feed line loss involved (as there always is) you will get a false
SWR reading. The more loss your cable has the better your SWR will
look.
This is because not only is there less power to reach the antenna that
is causing the reflection, but also there is less of the reflected
power that gets back to your SWR meter. It gets lost in the coax both
ways.

So if you have 3 db of line loss and your antenna has a 3:1 SWR, you
will only read it as about 1.4:1.

WHY:
With 3 db of line loss only 12.5 watts will make it to the antenna.
With a 3:1 SWR at that point 25% of the 12.5 watts (or 3.125 watts)
will be reflected back towards the SWR bridge. But the 3.125 watts
coming back down the cable will also undergo the 3 db of cable loss so
only .78 watts will show up as reflected power back at the SWR bridge.
That gets compared with the full 25 watts that the input of the SWR
bridge sees. The bridge will tell you that you have an SWR of only
about 1.4:1 when it is really 3:1!

Further, most SWR bridges are quite inaccurate at low readings. In the
area of 10 to 40%.

Even the revered Bird watt meter is not very accurate when reading on
the low end of the scale. It has a published accuracy of +- 5% of FULL
scale. Measuring a 25 watt radio, a 50 watt slug is normally used. 5%
of 50 watts is +-2.5 watts. Trying to read that 1.4:1 reflected power
level of .78 watts with a meter that has an error of +- greater than 3
times the level that you are trying to read leaves you guessing at
best!

Users of watt meters measuring reflected power often make the mistake
of seeing a few watts of reflected power and thinking things are "ok"
and not really calculating what they have, as the "reflected part is
rather low compared to the forward power". They equate it to an SWR
meter position comparison.

Bottom line is when using a watt meter on VHF to look at reflected
power, if the reflected indication is more than a division or two on
the meter you probably have to high an SWR.

With a short antenna cable, 20 or so feet, 1.5:1 SWR is about the
limit. With a longer cable, depending on its loss, The acceptable
limit may be much lower as seen above.

Some transmitters start shutting down their output at around 1.8:1
SWR.
So the problem with high SWR is not so much one of added loss as it is
a problem of the mismatch that the transmitter sees and reduces its
output power. Although with a high loss feed line you end up with less
of the reflected power to be re-reflected back up to the antenna.

Regards
Gary

How to use a simple SWR meter and what it means to your VHF
 

I started out in hf transmitters, 250kw ones. I don't remember SWR
being anything but a subject in theory for us. In practice we tuned
for max radiated power which was as good as it got.

Ron

How to use a simple SWR meter and what it means to your VHF
 

Yes a small portion of the re-reflected power that gets back to the
antenna is again reflected back toward the transmitter.

There are two ways to look at it. One is the steady state and the
other the dynamic. Once the line is charged with energy, if it a loss
less line, that energy that charged the line will bounce back and
forth continuously. The energy that is put into the line after that
will all reach the antenna and be radiated.

Easiest way to visualize it is with open wire line which has very low
loss. Feeding a non resonant antenna the SWR can be very high on the
line. You can have 50% reflected power on the line. With 100 watts
forward you would then have 50 watts reflected but just about all of
the 100 watts will reach the antenna and be radiated. The only loss
will be the very small loss in the line. (typically a few tenths of a
db loss)

If all the reflected power were to continually bounce back and forth
on the line you would only have half the power reaching the antenna to
be radiated. That doesn't happen except for the first instant that
power is applied and the line is charged with energy.

Regards
Gary



On Thu, 20 Nov 2003 23:47:27 +0100, "Meindert Sprang"
wrote:

"Gary Schafer" wrote in message
.. .
SWR in itself is not necessarily bad. Power reflected back toward the
transmitter is not lost as a result of the reflection itself. When
that reflected power hits the transmitter it is re-reflected back up
to the antenna.

And where it is reflected back into the cable again. And this continues
until the power is completely dissipated in by the losses in the path.

So a 3:1 swr with 6.25 watts of reflected power and 25 watts of
forward power, still delivers 25 watts to the antenna to be radiated.
That is of course when there is no feed line loss.

No. Power that is reflected the first time, will be reflected the secon time
it 'hits' the antenna. It wil NEVER be radiated.

Meindert