On Fri, 23 Apr 2004 05:06:19 -0000, Larry W4CSC
wrote:

In any HF radio installation, the closer the antenna is to resonance (1/4
wavelength long or 1/2 wavelength long) at the desired operating frequency,
and the further it is located in the clear from CONDUCTIVE surfaces, the
better it operates.


Why do you think an antenna operates better if it is resonant?

Regards
Gary

In order for an antenna to be a successful radiator of RF, it must radiate
TWO fields, hopefully towards the receiving station. The E-field is an
electrostatic field whos origin occurs at the high voltage points on the
antenna. In our short backstay case, that would be near the top insulator,
which is the highest impedance point in the wire. The H-field is a
magnetic field, 90 degrees physically from the E-field and expanding into
space with it. One field cannot exist without the other over great
distances, so the ideal situation is to have an antenna which creates both
intense E and H fields radiating in a pattern towards intended receivers.

on a vertical wire radiator (whip, backstay) the E field is vertical and
the H field is horizontal.

[whip tip or backstay insulator]
| E field max here, drops to near 0 1/4 wave down the wire
| then rises again to maximum 1/4 wave further down if wire
| is long enough
|
|
|
| H field max at tuner if wire is shorter than 1/4 wavelength. How
| much the field gets drops as wire gets to be less and less of 1/4
[tuner] wavelength.
|
|
[ground] The ground wire and ground create an "image", an imagined
antenna that looks (RF wise) like the radiator would in a mirror,
creating a vertical dipole antenna with the transmitter in the
middle.

The shorter our radiator, the poorer its H-field end-fed with tuner like
this.

As many of you have observed, really short HF whip antennas just suck as
radiators on the lower HF frequencies, getting worse as frequency
decreases. 2 Mhz marine band antennas all sucked because in comparison to
a full-sized 2 Mhz dipole, these antennas were REALLY short. This
"shortness", putting a short whip on top of a heavy tuner to get it to
resonate results in an intense E field from the high antenna VOLTAGE, but
almost no H field as there is little antenna CURRENT at any point in the
wire. The antenna current in this configuration occurs in the big loading
coil inside the tuner, which is causing the high voltage at its output
terminal at resonance. The current in this coil is NOT radiated as H
field, so your signal stinks at the receiver as distance increases, even
though your antenna system is resonant by the tuner's heavy inductance.

Gary Schafer wrote in
:


Why do you think an antenna operates better if it is resonant?


A self-resonant antenna, one that will load the transmitter without any
tuner in the circuit (or bypassed if your tuner will do that), creates the
maximum E and H fields at that frequency, when it is 1/4 wave, and at any
length LONGER than 1/4 wave we can tune it to. Longer isn't much of an
issue on a boat, unless you have room for the 107', quarter-wave tower on
old 2182 marine HF emergency channel. Our antennas are always shorter,
except above 12 Mhz where they become more reasonable in length.

The amount of H-field it creates as a too-short wire is also VERY dependent
on how much RF current we can make run to the ocean through its grounding
system. Great grounding, lots of current. Poor grounding, poor current,
poor H-field creation. E-fields are easy to make with tuner inductors. If
you'd like to see the effect of BIG E-field creation, go to my ham radio
callsign website on http://www.qrz.com/callsign/W4CSC and look at my
picture. I'm holding the bottom half of a 300 KV RF feedthrough insulator,
a souvenir of Reverend Stair (Overcomer Ministry's nut who broadcasts 24/7)
from his pirate radio ship that was temporarily docked in Charleston before
the FCC came to confiscate the 70KW HF transmitter that blew the hell out
of this insulator when it flashed over right above my head! MOST
impressive blast inside the fish hold of an old Canadian fishing trawler
where the transmitters were mounted. E-field is that big black arc down
the side of the porcelain...(c; 70KW on 41 meters is lots of fun. I love
high powered transmitters. "POWER is our FRIEND."

Sorry, I wandered off.....

Now, we hams have other solutions than this crappy tuner at the base of
your whip.....

Marine radio does what it does because it's quick and dirty (not to mention
yacht pretty with all its whitey fiberglass or stealth backstays). Tuners
are NOT a good thing, like this. We try not to use tuners on mobile HF
antennas on ham radio. Let's look at some that tune the ANTENNA to self-
resonance to create big H fields.....

http://www.texasbugcatcher.com/cata/tbcspec.htm
Henry Allen, K5BUG, has always produced the finest "loading coils" for ham
radio and other HF mobile antennas on the planet. My mobile antenna
configuration has two of them, but only when I'm operating in the 1.8-2.0
Mhz ham band BELOW the 2 Mhz marine band right on top of the AM broadcast
band. Above that band, I only use the #680 monstrous coil to tune an
antenna I designed 25 years ago that DRAGS THE CURRENT UP THE ANTENNA. The
antenna is 15' long, because the damned highway department says that's as
high as a truck can be. There are two ways of getting more CURRENT up the
antenna....put the antenna tuning coil about halfway up the length of
it...or...put a capacitor hat near the top of it in the E-field area. The
effect of doing this makes the antenna ELECTRICALLY LONGER, a lot longer,
without making it physically longer. My antenna has both! King Hussein,
JY1, the former King of Jordan, told my my signal was as strong as most
fixed stations. I have the QSL card from His Majesty to prove it...(c;
There is no tuner at the base of my antenna. The antenna is tuned to be
ELECTRICALLY, 1/4 wavelength long by adjusting a shorting tap on the huge
coil. Running 650 watts of RF power from a highly modified TenTec Hercules
II linear amp that's not legal on marine radio, the base feedpoint
impedance is about 18 ohms and produces over 6 AMPS of RF current to create
huge H-fields heard on the other side of the planet!

As you can see, no yachtie is going to let me put a 6" coil half way up the
backstay, so we have to put up with poor signals from the damned
tuners...(sigh) Geoffrey's "Lionheart", an Amel Sharki 41, does have
something I want to get modified to simulate the effect of the capacitor
hat of my ham antenna to make the HF wire longer. She has a triatic
between the top of the main and mizzen right over the insulator of the HF
insulated backstay on the main. I propose, if the masts ever get worked
on, to add two insulators to the triatic, near the mast tops, to insulate
it and connect a stainless cable from the antenna end of the backstay
insulator to a clamp in the middle of the triatic, creating a "top hat"
capacitor hat to DRAW UP that H-field current, making the antenna longer by
a good bit, Electrically.

Did this make more questions or answer them?? I love screwing around with
antennas. I've been doing it since before I got my ham license in 1957
when I was 11. Antennas and HF propagation are fascinating subjects....

Larry W4CSC, old 1st Phone w/Radar endorsement when it meant something...
S/V "Lionheart"
WDB6254 366920680

Contrary to popular myth, an antenna does not radiate one bit better
or worse if it is resonant or not.

With a short antenna the impedance gets to be really low. In the order
of an ohm or so with a typical 2 mhz antenna. The problem is getting
power to the low impedance antenna. Partly because of losses in
matching networks and partly because of ground impedance losses.

If you could get all the power into a 6" short antenna it would
radiate just as well as a full quarter wave length antenna.

The current is not less with a short antenna it is greater. That is
the reason for the higher loss. With a very short antenna the high
current in the antenna also causes losses. The current has to be
greater because the impedance is lower.
Nothing to do with the kind of fields that form around it.

Another myth is that you can change the electrical length of an
antenna by adding loading coils or other means.
Electrical length of an antenna is the same as it's physical length.
Plus a slight amount for propagation delay over it.

The physical length of an antenna IS also it's electrical length. You
can't change that.
What you can change is the matching to that antenna with inductors and
capacitors (or transmission line matching devices) to make the
antennas impedance and reactance match your transmitter.

There is no such thing as making a short antenna "look" like a quarter
wave antenna by adding a coil to it. Example: If you have a physical
1/8 wave length antenna you can not make it into a quarter wave length
antenna "electrically" by adding a loading coil to it. The coil may
serve to help match the antenna to the transmitter but you still have
an 1/8 wave length antenna electrically and physically.

And again: if you can get the same amount of power into the 1/8 wave
length antenna as you can get into a quarter wave length antenna, they
will radiate equally as well.

As far as using an antenna that is a quarter wave length long with a
tuner, you are probably better off with an antenna that is something
other than a quarter wave length as most tuners have a hard time
dealing with resonant antennas.

Regards
Gary

Gary Schafer wrote in
:

Contrary to popular myth, an antenna does not radiate one bit better
or worse if it is resonant or not.

It won't radiate much if it is not resonant. Try operating that 17' whip
with no tuner. The only thing a tuner does is resonate the antenna.


With a short antenna the impedance gets to be really low. In the order
of an ohm or so with a typical 2 mhz antenna. The problem is getting
power to the low impedance antenna. Partly because of losses in
matching networks and partly because of ground impedance losses.

Backwards. A 2' piece of wire on 2 Mhz has a feed point impedance damned
near infinity. A resonant wire 117' long, on the other hand, has a
feedpoint impedance of about 12-18 ohms if it's vertical close to ground.
The reason the 2' wire won't radiate on 2 Mhz is its impedance along its
entire length is so HIGH there isn't any antenna current to create an H-
field to radiate.


If you could get all the power into a 6" short antenna it would
radiate just as well as a full quarter wave length antenna.

Oh, if it were only true! All radio stations in the world could tear down
those big beautiful towers that are so costly. I can get 50KW into a 6"
antenna, but the voltage would be so high from the HIGH impedance we'd have
trouble trying to keep it from flashing over. Been there, done that.

The current is not less with a short antenna it is greater. That is
the reason for the higher loss. With a very short antenna the high
current in the antenna also causes losses. The current has to be
greater because the impedance is lower.
Nothing to do with the kind of fields that form around it.

Would you like to lay your boat's title on that? A very short antenna has
no current in it to speak of. Current in any radiator occurs at odd-
multiples of 1/4 wavelength back from the open end (insulator).

Another myth is that you can change the electrical length of an
antenna by adding loading coils or other means.
Electrical length of an antenna is the same as it's physical length.
Plus a slight amount for propagation delay over it.

Where DO you get this information? The entire purpose of adding series
coils and parallel capacitor hats is to vary the ELECTRICAL length of a
radiator, to make it electrically longer! The feedpoint impedance of my
15' long heavily-loaded (both with series coils and a large capacitor hat)
on 3.9 Mhz is around 12 ohms....just like a 1/4 wavelength vertical
radiator that is over 60 FEET long! The physical length is 15', the
electrical length is 64 FEET!


The physical length of an antenna IS also it's electrical length. You
can't change that.
What you can change is the matching to that antenna with inductors and
capacitors (or transmission line matching devices) to make the
antennas impedance and reactance match your transmitter.

There is no such thing as making a short antenna "look" like a quarter
wave antenna by adding a coil to it. Example: If you have a physical
1/8 wave length antenna you can not make it into a quarter wave length
antenna "electrically" by adding a loading coil to it. The coil may
serve to help match the antenna to the transmitter but you still have
an 1/8 wave length antenna electrically and physically.

And again: if you can get the same amount of power into the 1/8 wave
length antenna as you can get into a quarter wave length antenna, they
will radiate equally as well.

As far as using an antenna that is a quarter wave length long with a
tuner, you are probably better off with an antenna that is something
other than a quarter wave length as most tuners have a hard time
dealing with resonant antennas.

Regards
Gary

Gary, which university did you learn this from? What schooling in RF
engineering do you have? I'd like to take the course to expose them.

Larry W4CSC

"Boat electronics has nothing to do with PHYSICS and common sense."

On Sat, 24 Apr 2004 19:05:15 -0000, Larry W4CSC
wrote:

Gary Schafer wrote in
:

Contrary to popular myth, an antenna does not radiate one bit better
or worse if it is resonant or not.

It won't radiate much if it is not resonant. Try operating that 17' whip
with no tuner. The only thing a tuner does is resonate the antenna.

No, what the tuner does is match your feed line to your antenna.


With a short antenna the impedance gets to be really low. In the order
of an ohm or so with a typical 2 mhz antenna. The problem is getting
power to the low impedance antenna. Partly because of losses in
matching networks and partly because of ground impedance losses.

Backwards. A 2' piece of wire on 2 Mhz has a feed point impedance damned
near infinity. A resonant wire 117' long, on the other hand, has a
feedpoint impedance of about 12-18 ohms if it's vertical close to ground.
The reason the 2' wire won't radiate on 2 Mhz is its impedance along its
entire length is so HIGH there isn't any antenna current to create an H-
field to radiate.

Your 2' piece of wire has a high capacitive REACTANCE. In order to get
power into it you need an equal inductive reactance (coil) to cancel
the capactive reactance to make it appear resistive. That resistance
will be a very low value.

A quarter wave vertical antenna has an impedance of around 36 ohms by
the way.


If you could get all the power into a 6" short antenna it would
radiate just as well as a full quarter wave length antenna.

Oh, if it were only true! All radio stations in the world could tear down
those big beautiful towers that are so costly. I can get 50KW into a 6"
antenna, but the voltage would be so high from the HIGH impedance we'd have
trouble trying to keep it from flashing over. Been there, done that.

Please tell us how you can get 50 kw into a 6" antenna at HF? This is
the problem that I am telling you. Losses are so high in the antenna
and matching network that little power makes it to the antenna.

But what power you do get into it will radiate just as well as the
same amount of power in a larger antenna.


The current is not less with a short antenna it is greater. That is
the reason for the higher loss. With a very short antenna the high
current in the antenna also causes losses. The current has to be
greater because the impedance is lower.
Nothing to do with the kind of fields that form around it.

Would you like to lay your boat's title on that? A very short antenna has
no current in it to speak of. Current in any radiator occurs at odd-
multiples of 1/4 wavelength back from the open end (insulator).

You are confusing reactive power with real power.

Remember in tech school when they showed you an inductor and a
capacitor in series and applied a specific amount of AC voltage. You
were asked if the voltage across the inductor or capacitor could be
higher than the applied voltage?


Another myth is that you can change the electrical length of an
antenna by adding loading coils or other means.
Electrical length of an antenna is the same as it's physical length.
Plus a slight amount for propagation delay over it.

Where DO you get this information? The entire purpose of adding series
coils and parallel capacitor hats is to vary the ELECTRICAL length of a
radiator, to make it electrically longer! The feedpoint impedance of my
15' long heavily-loaded (both with series coils and a large capacitor hat)
on 3.9 Mhz is around 12 ohms....just like a 1/4 wavelength vertical
radiator that is over 60 FEET long! The physical length is 15', the
electrical length is 64 FEET!

If that were true then why wouldn't the feed point impedance of your
15 foot antenna be around 36 ohms like the full quarter wave length
vertical?

Sorry but your electrical length is only 15 feet. The same as the
physical length.
Your coil only serves as a matching device between the two sections of
antenna. It is canceling out the capacitive reactance.


The physical length of an antenna IS also it's electrical length. You
can't change that.
What you can change is the matching to that antenna with inductors and
capacitors (or transmission line matching devices) to make the
antennas impedance and reactance match your transmitter.

There is no such thing as making a short antenna "look" like a quarter
wave antenna by adding a coil to it. Example: If you have a physical
1/8 wave length antenna you can not make it into a quarter wave length
antenna "electrically" by adding a loading coil to it. The coil may
serve to help match the antenna to the transmitter but you still have
an 1/8 wave length antenna electrically and physically.

And again: if you can get the same amount of power into the 1/8 wave
length antenna as you can get into a quarter wave length antenna, they
will radiate equally as well.

As far as using an antenna that is a quarter wave length long with a
tuner, you are probably better off with an antenna that is something
other than a quarter wave length as most tuners have a hard time
dealing with resonant antennas.

Regards
Gary

Gary, which university did you learn this from? What schooling in RF
engineering do you have? I'd like to take the course to expose them.

Read any of your mobile radio antenna handbooks. They will explain the
basics in there on short antennas.

Also in your regular antenna handbook read about an all band 112'
dipole fed with open wire feed line. Not resonent on ANY band.

Regards
Gary

Larry W4CSC

"Boat electronics has nothing to do with PHYSICS and common sense."

Gary Schafer wrote in
:

Ok, uncle, you win......

Everything everyone teaches is wrong, including me....

Gary Schafer wrote in
:

Ok, uncle, you win......

Everything everyone teaches is wrong, including me....

On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote:
Your 2' piece of wire has a high capacitive REACTANCE. In order to get
power into it you need an equal inductive reactance (coil) to cancel
the capactive reactance to make it appear resistive.

=============================================

I follow what you are saying but isn't that also the definition of
resonance, i.e., the point where capacitive reactance cancels
inductive reactance?

On Sun, 25 Apr 2004 08:56:23 -0400, Wayne.B
wrote:

On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote:
Your 2' piece of wire has a high capacitive REACTANCE. In order to get
power into it you need an equal inductive reactance (coil) to cancel
the capactive reactance to make it appear resistive.

=============================================

I follow what you are saying but isn't that also the definition of
resonance, i.e., the point where capacitive reactance cancels
inductive reactance?


When you cancel the capacitive reactance seen at the bottom of the
antenna with an equal amount of inductive reactance you see a pure
resistance at the other end of the coil (transmitter end). But that
does not change anything in the antenna itself.

The shorter an antenna is (from a quarter wave length) the lower it's
radiation resistance is. If you want to put the same amount of power
into it as you did when it was longer then you must put more current
into it. Just simple ohms law at this point. As long as you are
dealing with pure resistance, which you are when you cancel the
reactance.

However, you can not use simple ohms law when dealing with a
reactance, which is what Larry is trying to do. Yes there will be very
high voltages at the output of the antenna tuner with a short antenna
connected to it. But it is because of the reactance of the coil. That
voltage is not in phase with the current at that point.

Take the example that I posed to Larry about the capacitor and
inductor in series connected to an AC supply. There will be a specific
amount of current flowing in the circuit. You will measure a voltage
across the inductor. That voltage can be much higher than the voltage
from the AC supply. If you multiply that voltage by the circuit
current it will appear as though you have more power in the circuit
than what the AC supply is actually putting out! That looks like free
energy!

You have to take into account the phase shift (also called power
factor) that happens across the inductor.

The same thing happens with the antenna tuner situation.

You can not say "because the voltage is high the current must
therefore be low", like Larry wants to do.

The voltage is high and so is the current. BUT THEY ARE NOT IN PHASE.
There are extremely high currents in the system. The high current in
the coil is what causes I squared R loss (power lose).

In the information in my other post about short antennas, the coil has
a resistance of around 10 ohms and the radiation resistance of the
short antenna was only .3 ohms. So you can see that the coil will suck
up most of the power. That is why a short antenna is less efficient
than a longer one. Not because a short antenna radiates poorer than a
longer one.

An antenna will radiate just as well if it is resonant or not.
Provided you get the same amount of power to it.

The E field and H field of an antenna aren't necessarily the same.
They do balance themselves out as they propagate in free space. Has
nothing to do with how well it radiates.

Regards
Gary

On Sun, 25 Apr 2004 08:56:23 -0400, Wayne.B
wrote:

On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote:
Your 2' piece of wire has a high capacitive REACTANCE. In order to get
power into it you need an equal inductive reactance (coil) to cancel
the capactive reactance to make it appear resistive.

=============================================

I follow what you are saying but isn't that also the definition of
resonance, i.e., the point where capacitive reactance cancels
inductive reactance?


When you cancel the capacitive reactance seen at the bottom of the
antenna with an equal amount of inductive reactance you see a pure
resistance at the other end of the coil (transmitter end). But that
does not change anything in the antenna itself.

The shorter an antenna is (from a quarter wave length) the lower it's
radiation resistance is. If you want to put the same amount of power
into it as you did when it was longer then you must put more current
into it. Just simple ohms law at this point. As long as you are
dealing with pure resistance, which you are when you cancel the
reactance.

However, you can not use simple ohms law when dealing with a
reactance, which is what Larry is trying to do. Yes there will be very
high voltages at the output of the antenna tuner with a short antenna
connected to it. But it is because of the reactance of the coil. That
voltage is not in phase with the current at that point.

Take the example that I posed to Larry about the capacitor and
inductor in series connected to an AC supply. There will be a specific
amount of current flowing in the circuit. You will measure a voltage
across the inductor. That voltage can be much higher than the voltage
from the AC supply. If you multiply that voltage by the circuit
current it will appear as though you have more power in the circuit
than what the AC supply is actually putting out! That looks like free
energy!

You have to take into account the phase shift (also called power
factor) that happens across the inductor.

The same thing happens with the antenna tuner situation.

You can not say "because the voltage is high the current must
therefore be low", like Larry wants to do.

The voltage is high and so is the current. BUT THEY ARE NOT IN PHASE.
There are extremely high currents in the system. The high current in
the coil is what causes I squared R loss (power lose).

In the information in my other post about short antennas, the coil has
a resistance of around 10 ohms and the radiation resistance of the
short antenna was only .3 ohms. So you can see that the coil will suck
up most of the power. That is why a short antenna is less efficient
than a longer one. Not because a short antenna radiates poorer than a
longer one.

An antenna will radiate just as well if it is resonant or not.
Provided you get the same amount of power to it.

The E field and H field of an antenna aren't necessarily the same.
They do balance themselves out as they propagate in free space. Has
nothing to do with how well it radiates.

Regards
Gary