[Elecraft] Random length wire for use with KX3

[Ron D'Eau Claire]

Note that the article referenced suggests avoiding multiples of 1/2
wavelength if you are trying to feed it with a 50 ohm transmitter with *no*
matching network or ATU. That is not true for a system that includes an ATU.


The closer you can get to 1/2 wavelength, the more efficient the antenna
will be for a given 'ground' setup providing your ATU can match the
transmitter output to the impedance. That's because at 1/2 wavelength
relatively little current flows into the antenna and so relatively little
current flows into the "ground" system, which greatly reduces losses in the
"ground" system. Ground system losses are the majority of losses in an end
fed wire. (I put ground in "" because it is really just a low RF impedance
point, whether it connects to the earth or not. It can just as well be a 1/4
wavelength counterpoise, a gazillion wires, or anything in between.)

Indeed, exactly 1/2 wavelength would be the ideal length for an efficient
end fed wire except that most automatic tuners cannot match the very high
impedance present or handle the very high RF voltages involved at the feed
point. Many old manual tuners could, which is why they are physically huge,
using variable capacitors with very wide spacing, big ceramic insulators,
etc. 

So the "trick" for highest efficiency in an end fed wire with modern compact
tuners is to get as close to 1/2 wavelength as the tuner can match.
Unfortunately that can only be done on one band, but if you do that on the
lowest frequency band you are usually good across the HF spectrum since the
swing in impedance value from maximum to minimum gets less and less with
each wavelength multiple. Depending upon your tuner's matching range and
other factors, you may still find another band where the impedance is out of
range. In that case the only solution is to find a compromise length if you
really want to quickly hop all over the HF spectrum. 

73, Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Calvin
Sent: Friday, November 09, 2012 2:01 PM
To: Joseph Trombino, Jr
Cc: Elecraft at mailman.qth.net
Subject: Re: [Elecraft] Random length wire for use with KX3

Hi, this looked like a good article that talked about random wire lengths.

http://www.hamuniverse.com/randomwireantennalengths.html

I am interested in trying it out when my Kx3 arrives.

73's
KA7MAY

Sent from my iPad

On Nov 9, 2012, at 2:33 PM, "Joseph Trombino, Jr" <w2kj at bellsouth.net>
wrote:

> Howdy Gang:
> 
> Nice WX tomorrow for our neck of the woods (southeastern North Carolina)
so I'm gonna take my KX3 out and play radio.
> 
> I have the internal tuner installed and am wondering if anyone has had
success with a particular length of antenna wire with the tuner in the KX3??
> 
> I usually use a PAR EFHW for 40/20/10M but wanted to play with something
different and also give the internal tuner a spin around the block.
> 
> So, what lengths of wire have been used successfully with the KX3??
> 
> Many thanks for any info....will be on the air shortly after lunch
time...1800Z or 1900Z....will be looking for you around the QRP watering
holes on CW.
> 
>                73, Joe W2KJ
>                I QRP, therefore I am
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