Tom Donaly wrote:
And, if the total electrical length isn't 90 degrees, you
add a few degrees to the loading coil to make it come out right.
Very ingenious.

Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Tom Donaly wrote:
And, if the total electrical length isn't 90 degrees, you
add a few degrees to the loading coil to make it come out right.
Very ingenious.

Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.

Suuurrrre it is. You've got 90 degrees on the brain, Cecil.
Next, you'll be talking about 90 degree equilibrium.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
Cecil Moore wrote:
Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.

Suuurrrre it is. You've got 90 degrees on the brain, Cecil.
Next, you'll be talking about 90 degree equilibrium.

The technical content of your posting is noted, Tom.
I gave you the opening to nail my hide to the wall.
Is this the best technical argument that you have?

Please describe how 45 electrical degrees of transmission
line can be brought to 1/4WL resonance without help
from discrete components.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote
Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.
_______________

It may have the reactance of an unloaded ~90-degree, self-resonant radiator.
But in normal applications that doesn't make a screwdriver the radiational
equivalent of that full-sized radiator, because the radiation resistance of
the physically/electrically short screwdriver whip is less than a full-sized
antenna -- and much less on the lower bands.

A dummy load can have the reactance of a resonant screwdriver, too, but a
dummy load is not a very good antenna. I doubt you would claim that it is
electrically 90 degrees in length, just because it has the same reactance as
an unloaded ~90 degree, self-resonant monopole.

That conclusion applies to a screwdriver antenna system, as well.

RF

Richard Fry wrote:
"Cecil Moore" wrote
Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.

Note that the electrical length and the physical length
are nowhere near the same value. The electrical length
can be 90 degrees at resonance while the physical length
is only 13 degrees for a 75m mobile antenna.

It may have the reactance of an unloaded ~90-degree, self-resonant
radiator. But in normal applications that doesn't make a screwdriver the
radiational equivalent of that full-sized radiator, because the
radiation resistance of the physically/electrically short screwdriver
whip is less than a full-sized antenna -- and much less on the lower bands.

I agree 100% and have never disagreed. I have already stated
that the radiation characteristics of an antenna depend upon
its *physical* length while the feedpoint impedance depends
upon its *electrical* length. A screwdriver antenna may be
only 13 degrees long *physically* on 75m. Of course, it is
NOT going to radiate like a physical 90 degree antenna. It
is going to radiate more like a 13 degree (short) antenna.

You have apparently misunderstood what I am trying to say.
I have made *zero assertions about radiation patterns* except
to answer your earlier posting on that subject.

A dummy load can have the reactance of a resonant screwdriver, too, but
a dummy load is not a very good antenna. I doubt you would claim that
it is electrically 90 degrees in length, just because it has the same
reactance as an unloaded ~90 degree, self-resonant monopole.

A dummy load's feedpoint impedance is not (Vfor+Vref)/(Ifor+Iref),
i.e. not a virtual impedance, so your comment is irrelevant in
this context. The IEEE Dictionary distinguishes between those
two definitions of impedance, (B) for an antenna, (C) for a
dummy load.

That conclusion applies to a screwdriver antenna system, as well.

Since it is possible to tune a screwdriver antenna to the
270 degree mode, the following will assume the screwdriver
antenna system is used only in the 90 degree mode:

A screwdriver antenna system has radiation characteristics
appropriate for its *physical* length of, e.g. 13 degrees.
A screwdriver antenna system with a low resistive feedpoint
impedance is electrically 90 degrees long because
(Vfor+Vref)/(Ifor+Iref) is resistive. The only way for Vfor
and Vref to be 180 degrees out of phase is for the antenna
to be electrically 90 degrees long. The only way for Ifor
and Iref to be in phase is for the antenna to be electrically
90 degrees long. That's simple wave reflection model physics.

In abandoning the wave reflection model, many people have
abandoned any possibility of understanding what happens
in a standing-wave antenna. Sooner or later, their short
cut methods bite them in the posterior. The W8JI and W7EL
current measurements are an example.

Anyone who never looks for the "missing" phase shifts in
a mobile antenna will never find them. Side 1 of the
argument assumes they are not there. Side 2 of the argument
assumes they are there in the loading coil. Both sides
are wrong. I have gone looking for the "missing" phase
shifts and have found them. Here is a lossless transmission
line example which is *physically 45 degrees long*:

---Z0=600, 22.5 degrees---+---Z0=100, 22.5 degrees---open

What is the impedance looking into the stub? Where are the
"missing" 45 degrees?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

...
Note that the electrical length and the physical length
are nowhere near the same value. The electrical length
can be 90 degrees at resonance while the physical length
is only 13 degrees for a 75m mobile antenna.
...

I have been thinking on this. From past posts, I think some think that
a 1/4 wave monopole and a 1/2 wave electrical length monopole shortened
to 1/4 physical length have very similar launch/radiation
characteristics... if they do, then it is obvious that their modeling
program is "BLOWING SMOKE!"

A 90 degree shift in 1/4 wave physical space will never duplicate a 180
shift in the same physical dimensions!

Regards,
JS

John Smith wrote:
A 90 degree shift in 1/4 wave physical space will never duplicate a 180
shift in the same physical dimensions!

It certainly will never duplicate the radiation pattern
which depends upon physical dimensions. But it may come
close to duplicating the feedpoint impedance which is
what this discussion is about.
--
73, Cecil http://www.w5dxp.com