Well that is indeed food for thought thanks Cecil! I have never heard of
that before, but it certainly figures. I just wound another for 20m,
with abt 46 feet of wire on it, and it GDO's on approx 48 MHz ONLY!
Although the GDO coupled into the z bridge says it is resonant at 14250,
20 ohms. But the SWR is hopeless!
Now it figures....I was going to re-wind the same wire onto another
thicker whip and see what happens to the resonant freq.

Do you think it might help if I keep the close wound section to a half
wave or less, and make the remainder above and below the coil well
spaced? I know I'll need to try I guess as each antenna I try is different.
I am going to make a dummy test rig of mounting a mobile base on a piece
of scrap iron, with a simple 2-3 turn loop on the base. No coax. Then I
can GDO any antenna I screw onto it! I'm gunna solve this!
All observations appreciated!
Adrian.

Oops, almost missed this......

Cecil Moore wrote:
A length of 3/4 wavelength of wire is suggested
there.


By who?

Someone quoted ARRL handbook chapter on mobile ants.

mustang wrote:
Do you think it might help if I keep the close wound section to a half
wave or less, and make the remainder above and below the coil well
spaced?

Here's what I would try as a wild hair experiment. Wind the electrical 1/2WL
helix and find the frequency at which the impedance is purely resistive and
maximum. A GDO should accomplish that. That's the resonant frequency for an
end-fed 1/2WL monopole. Use some spacing and wind the remainder of the coil
opposite to the original, i.e. CW Vs CCW. This would theoretically put the
fields in phase on each side of that current node. It sounds very tricky and
I have never heard of it being done before, but it might work.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

mustang wrote:
Do you think it might help if I keep the close wound section to a half
wave or less, and make the remainder above and below the coil well
spaced?

Here's what I would try as a wild hair experiment. Wind the electrical
1/2WL helix and find the frequency at which the impedance is purely resistive and
maximum. A GDO should accomplish that. That's the resonant frequency for an
end-fed 1/2WL monopole. Use some spacing and wind the remainder of the coil
opposite to the original, i.e. CW Vs CCW. This would theoretically put the
fields in phase on each side of that current node. It sounds very tricky
and I have never heard of it being done before, but it might work.

And of course, this would work perfectly on only a single frequency. Off
to each side of that frequency, the problem would again manifest itself.
--
73, Cecil http://www.qsl.net/w5dxp



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Hmm, an interesting approach!
But its all about trying things!
I'll give that one a go too. It doesn't take long to wind & try!
Adrian.




Here's what I would try as a wild hair experiment. Wind the electrical
1/2WL helix and find the frequency at which the impedance is purely
resistive and
maximum. A GDO should accomplish that. That's the resonant frequency
for an
end-fed 1/2WL monopole. Use some spacing and wind the remainder of the
coil
opposite to the original, i.e. CW Vs CCW. This would theoretically put
the
fields in phase on each side of that current node. It sounds very
tricky and I have never heard of it being done before, but it might work.


And of course, this would work perfectly on only a single frequency. Off
to each side of that frequency, the problem would again manifest itself.