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."