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

On Sat, 22 Nov 2003 08:11:49 +0100, "Meindert Sprang"
wrote:

"Gary Schafer" wrote in message
.. .
On Fri, 21 Nov 2003 20:12:32 +0100, "Meindert Sprang"

You obviously don't understand how this works. The combination of antenna
and feedline presents a certain impedance at the end of the feedline.
What
the tuner does is transform the 50 Ohm on the TX side to the impedance on
the feedline. And when this all matches, there is no SWR. Neither on the
TX
side of the tuner, nor on the feedline side.

Meindert
pe1grv



Wann bet? :)

Try it some time. Tune the tuner so there is no SWR at the
transmitter. Then place the SWR meter between the tuner and the
transmission line. You will still see the same SWR that you started
with!

Of course you will. That's because you put the SWR meter on a place where
the impedance is not 50 Ohm anymore. So now you have a mismatch between the
feedline and 50 Ohm directional coupler in the SWR meter.

Meindert



Exactly the same thing you started with isn't it!

Regards
Gary

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

In article ,
"Doug Dotson" wrote:

I think we all kind of sort of knew this Bruce.

Doug

"Bruce in Alaska" wrote in message
...
I suspect that there is a big misunderstanding of TERMS, going on here.
Definitions are being misused on both sides......

Lets get the TERMS Fixed and Understood first.

Transmitter = Rf Source that has an impedance of 50 Ohms

Transmission Line = Coaxial Feedline between Transmitter and Antenna
Tuner.
Antenna Tuner = Device that matches impedance of it's input (50 Ohms)
to that of the antenna that connects to the tuners
output.
Antenna = Effectivly a wire, or pipe, or other conducting structure
used to radiate RF Energy supplied by the Transmitter to
the feedline.

NOW that we have these definitions settled, Please continue the
discussion.

Bruce in alaska
--
add a 2 before @



Really, then why are folks talking about SWR on the Feedline as being 3:1
or sum such when the feedline in reference system above would have no
SWR as it is at 50 Ohms on both ends???? TERMS are significant, and
Larry, and the rest are mixing them thoughout this whole thread.

Bruce in alaska
--
add a 2 before @

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

In article ,
Gary Schafer wrote:

One exception, in this case we are talking about an antenna tuner with
its output going to a coax line that then goes to the antenna. The
antenna being something near 50 ohms but far enough from it to produce
a 3:1 SWR on its feed line.

So in this case we have 2 transmission lines. One between the
transmitter and the tuner and one between the tuner and the antenna.

Regards
Gary



Actually, in the "Marine Radio" context anything that connects to
the High Impedance side of the tuner is considered not Feedline
but part of the antenna. OK, if just call that part "Transmission Line"
rather than a second feedline? this will allow discussee's to
differentate between the two pieces of the reference system, and
not get them confused while making their points.....

Bruce in alaska
--
add a 2 before @

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

On Sat, 22 Nov 2003 19:01:50 GMT, Bruce in Alaska
wrote:

In article ,
Gary Schafer wrote:

One exception, in this case we are talking about an antenna tuner with
its output going to a coax line that then goes to the antenna. The
antenna being something near 50 ohms but far enough from it to produce
a 3:1 SWR on its feed line.

So in this case we have 2 transmission lines. One between the
transmitter and the tuner and one between the tuner and the antenna.

Regards
Gary



Actually, in the "Marine Radio" context anything that connects to
the High Impedance side of the tuner is considered not Feedline
but part of the antenna. OK, if just call that part "Transmission Line"
rather than a second feedline? this will allow discussee's to
differentate between the two pieces of the reference system, and
not get them confused while making their points.....

Bruce in alaska


Well, this thing started out as a discussion of SWR on a 50 ohm VHF
feed line. Nothing to do with HF single ended antennas and associated
couplers.

HF got mixed in to the discussion because most are familiar with coax
line antenna tuners. 50 ohm in 50 ohm or near that out. The principles
are the same of course.

With HF things are a little easier to manipulate to do test on than
VHF.

My referring to "feed line" or "transmission line" are all referring
to coax cable. One is synonymous with the other.

I think most are using the same terms.

Sorry for any confusion.

Regards
Gary

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

TERMS are significant.

Bruce,

Don't say that too loud. I've already been down that road with Jax.

Ron

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

On Fri, 21 Nov 2003 18:32:56 GMT, Gary Schafer
wrote:

You need to tune your tuner only to provide the proper impedance match
to your transmitter. A 50 ohm SWR bridge at the transmitter will tell
you when you have achieved that.

WHOA! There you go again! If I tune my transmitter to 50 ohms
RESISTIVE, non-reactive, it will ABSORB any reflected power because
it's acting like a RESISTOR, as it should, converting reflected power
into HEAT in the final amp.....(c;


Larry W4CSC

NNNN

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

I feel like the Aflack duck running out of Yogi Berra's barber shop
shaking his head....(c;

Larry W4CSC

NNNN

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

On Sun, 23 Nov 2003 14:43:26 GMT, (Larry W4CSC) wrote:

On Fri, 21 Nov 2003 18:32:56 GMT, Gary Schafer
wrote:

You need to tune your tuner only to provide the proper impedance match
to your transmitter. A 50 ohm SWR bridge at the transmitter will tell
you when you have achieved that.

WHOA! There you go again! If I tune my transmitter to 50 ohms
RESISTIVE, non-reactive, it will ABSORB any reflected power because
it's acting like a RESISTOR, as it should, converting reflected power
into HEAT in the final amp.....(c;


Larry W4CSC

NNNN


I see you haven't read your Bird manual yet about power delivered to
the load have you Larry. :)

ARRL HANDBOOK CHAPTER AND VERSE:
Here is some stuff right out of the 2000 ARRL Handbook. Chapter 19:
Transmission Lines. Page 3, Mismatched lines: Look at the 5th
paragraph there if you don't want to read the rest. It tells you what
happens to reflected power traveling back down the line.

It says that if it encounters a mismatch at the load, part of the
energy gets reflected back down the line. "It (reflected energy)
encounters another mismatch at the generator. Reflected energy flows
back toward the load. After a few such journeys it diminishes to
nothing. Partly because of loss in the line but mostly because it is
absorbed by the load. If the load is an antenna that energy will be
radiated."

FURTHER:
Look at page 19.7. There is a table there showing the line losses and
SWR encountered with a 100 foot flat top antenna at different
frequencies. With that antenna at 7 mhz the SWR on RG8 would be
49.1:1. The loss would be 5.8 db on 100 feet of cable. With open wire
feed line the loss would be .3 db.

If all the reflected power got dissipated in the finals of the
transmitter at an SWR of 49:1 you wouldn't have much left to radiate.

STILL NOT A BELIEVER ?:
Do the simple experiment with your watt meter and the tuner that I
described before. If you have 2 watt meters, one to put on each side
of the tuner, all the better.

Don't forget to read that little paragraph in the Bird manual about
"power delivered to the load".

It is forward power minus reflected power. But note that THE FORWARD
POWER READING ON THE WATT METER WILL BE THE TRANSMITTER POWER PLUS THE
REFLECTED POWER. As the mismatch at the load end of the line is
increased so does the "apparent forward power" on the watt meter in
that line increase.

If anyone that is interested doesn't have an ARRL handbook or can't
find it in their version let me know on the news group and I will scan
the page for you. Let me know here as I don't look at this email
address very often.

Regards
Gary

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

So what is the use of an SWR meter if SWR has no affect on
radiated power or stress on the finals? I know for a fact that if
I tune my antenna for lowest SWR, I have a better signal.

Doug

"Gary Schafer" wrote in message
...
On Sun, 23 Nov 2003 14:43:26 GMT, (Larry W4CSC) wrote:

On Fri, 21 Nov 2003 18:32:56 GMT, Gary Schafer
wrote:

You need to tune your tuner only to provide the proper impedance match
to your transmitter. A 50 ohm SWR bridge at the transmitter will tell
you when you have achieved that.

WHOA! There you go again! If I tune my transmitter to 50 ohms
RESISTIVE, non-reactive, it will ABSORB any reflected power because
it's acting like a RESISTOR, as it should, converting reflected power
into HEAT in the final amp.....(c;


Larry W4CSC

NNNN


I see you haven't read your Bird manual yet about power delivered to
the load have you Larry. :)

ARRL HANDBOOK CHAPTER AND VERSE:
Here is some stuff right out of the 2000 ARRL Handbook. Chapter 19:
Transmission Lines. Page 3, Mismatched lines: Look at the 5th
paragraph there if you don't want to read the rest. It tells you what
happens to reflected power traveling back down the line.

It says that if it encounters a mismatch at the load, part of the
energy gets reflected back down the line. "It (reflected energy)
encounters another mismatch at the generator. Reflected energy flows
back toward the load. After a few such journeys it diminishes to
nothing. Partly because of loss in the line but mostly because it is
absorbed by the load. If the load is an antenna that energy will be
radiated."

FURTHER:
Look at page 19.7. There is a table there showing the line losses and
SWR encountered with a 100 foot flat top antenna at different
frequencies. With that antenna at 7 mhz the SWR on RG8 would be
49.1:1. The loss would be 5.8 db on 100 feet of cable. With open wire
feed line the loss would be .3 db.

If all the reflected power got dissipated in the finals of the
transmitter at an SWR of 49:1 you wouldn't have much left to radiate.

STILL NOT A BELIEVER ?:
Do the simple experiment with your watt meter and the tuner that I
described before. If you have 2 watt meters, one to put on each side
of the tuner, all the better.

Don't forget to read that little paragraph in the Bird manual about
"power delivered to the load".

It is forward power minus reflected power. But note that THE FORWARD
POWER READING ON THE WATT METER WILL BE THE TRANSMITTER POWER PLUS THE
REFLECTED POWER. As the mismatch at the load end of the line is
increased so does the "apparent forward power" on the watt meter in
that line increase.

If anyone that is interested doesn't have an ARRL handbook or can't
find it in their version let me know on the news group and I will scan
the page for you. Let me know here as I don't look at this email
address very often.

Regards
Gary

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

Agreed!

"Larry W4CSC" wrote in message
...
I feel like the Aflack duck running out of Yogi Berra's barber shop
shaking his head....(c;

Larry W4CSC

NNNN