Topband: Length of inverted-L antenna for use with K2AV counterpoise

[Guy Olinger K2AV]

Steve, the length of the wire is your choice, with consequences in the
tuning realm.

The simple solution is to only use the wire on 160, and VARY THE LENGTH of
the wire to achieve a minimum SWR or zero reactance at 1.825, or your
choice of center of resonance.

If the length is fixed (your choice) and the radiator is really short you
will need a series inductor, and really long a series capacitor, with a
feed Z that depends on the length and configuration of the wire.

For the simple solution, neither the series inductor or cap is used, and
the length is pruned for resonance, just like a dipole. This resonant
length will vary, depending heavily on the environment, type of dirt, just
like a dipole.  It will also produce a Z that is decent for transmission
across 50 ohm coax, and if not close enough to 50 ohms as is, is easily
handled by whatever tuner may be in the shack.

Obviously we don't have reports from several hundred people who have done
this, but the simple solution seems to work out something a little longer
than a quarter wave, though it is clear from the small sample so far, that
this varies a lot on how one is able to get the wire up.

Mine is 3/8 wave, up 90 and out 105, and I use a series vacuum cap to tune
it.  I also use a 4:1 isolation transformer to up-convert the 90 resonant Z
to 360 ohms to match 424 feet of Wireman #554 "450" window line.  This is
obviously not the "simple" solution.

What you do in addition to the isolation transformer and the FCP is just as
variable as it ever was.

73, Guy.

On Fri, Dec 9, 2011 at 4:46 AM, Steve Ireland <vk6vz at arach.net.au> wrote:

> Hi Jack
>
>
>
> One question in regard to your drawing of the 160m antenna you use with
> K2AV's FCP counterpoise.  Are you using a resonant quarter wave antenna
> (i.e. about 132' total length) with the counterpoise, or an extended
> inverted 5/16 or 3/8 wave antenna?  I am guessing the former, but am also
> wondering if you have tried to use the latter, tuned with a series
> capacitor
> to remove the inductive reactance at the feedpoint.
>
>
>
> In the drawing, the length of the horizontal top section of your inverted-L
> is given (84.5 feet), but not the length of the vertical bottom section.
>
>
>
> Vy 73
>
>
>
> Steve, VK6VZ
>
>
>
>
>
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