Re: Re: Elecraft Digest, Vol 8, Issue 10

Posted by Vic K2VCO on Dec 10, 2004; 5:34pm
URL: http://elecraft.85.s1.nabble.com/Re-Elecraft-Digest-Vol-8-Issue-10-tp372455p372460.html

Mychael Morohovich wrote:

> Instead of a 1/4 wl wire, I use an MFJ Artificial Ground to tune a wire for
> maximum current per given band. While measuring, one thing that
> surprised me was to discover that with my 86' EFW, the use of a properly
> tuned counterpoise didn't always increase the current to the radiator.
> For example, on 40 meters the use of a counterpoise helped
> to realize a substantial increase of current into the radiator, while on 80
> meters I actually saw more current into the radiator with the counterpoise
> unhooked on that band. The effects on 30-10 were really fairly minimal or
> neutral in this regard.

Keep in mind that you are measuring the current in the radiator AT A PARTICULAR
POINT.  Due to the standing waves on the radiator, that current varies depending
on where you measure it.  Now, since the 'antenna' you are feeding consists of
the counterpoise PLUS the radiator, tuning the counterpoise will change the
current distribution on the whole system.  So measuring the current at the
original point on the radiator does not tell the whole story.  Perhaps adding
the counterpoise has moved the maximum current point away from the feedpoint (a
desirable situation)?

What you can do is listen to distant stations while connecting and disconnecting
the counterpoise.  That will test the overall effectiveness of the antenna.  Of
course, the counterpoise will also change the horizontal and vertical pattern of
the antenna, so you will need to listen to a large number of distant stations to
  control for this effect!

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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