Hi Guy
Thanks for the reply - most interesting and helpful. I like your conversion
idea for the 450' ohm ladder line - like open wire line here too.
I did have an 160m inverted-L antenna here with a Moxon-type counterpoise
about ten years ago and it was a very useful antenna. However, your
counterpoise idea looks like a definite improvement and it would be good to
have a choice of polarization here again. Most of my 160m DX has been
worked with a cloud-warmer inverted-vee dipole antenna just before sunrise
or just after sunset, but the old inverterted L was better on middle
distances, particularly out into the Pacific, and there are some countries
that I still need out there.
I shall have some fun building one of your counterpoises in the New Year
(and an inverted-L to go with it)!
Vy 73
Steve, VK6VZ
_____
From: guyk2av@gmail.com [mailto:guyk2av@gmail.com] On Behalf Of Guy Olinger
K2AV
Sent: Saturday, 10 December 2011 1:04 AM
To: Steve Ireland
Cc: w0uce@nc.rr.com; topband@contesting.com
Subject: Re: Topband: Length of inverted-L antenna for use with K2AV
counterpoise
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.
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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