[Elecraft] KX1: requesting recommended wire antenna lengths advice

[J]

Pat and the List;

A few ideas:

First:  
To rule out any issues with the ATU on 40M, you might try tuning on 40M into
a wattmeter with dummy load.  Also, compare 40M with no ATU enabled to 40M
with the ATU enabled, using the same dummy load and wattmeter.  Go over all
of the KXATU tests and diagnostics for the three bands.

Next:
Assuming 40M is working with your ATU, try alternate antenna and
counterpoise lengths.  I saw somewhere using two counterpoise wires of 16
feet each and I do this.  You might also add a 30 or 33 foot counterpoise to
help on 40M.  

A rule-of-thumb is to avoid anything which is 1/2 wavelength or a multiple
thereof for the antenna.  Half-wavelength antennas are high impedance at the
feedpoint; above the range of the ATU in the KX1.  For example, 33 feet may
work well on 40M, but is a half-wavelength on 20 and would have difficulty
tuning on 20M.

I've used 40-42 feet for my radiator with two 16 foot counterpoise radials.
It seemed to avoid a half-wavelength on 30M (which would be 46.3 feet) and
worked on three bands.

These short (28 foot) wire antennas and single, short radials will work on
the three bands and the short lengths make it easy to hang from a balcony,
tree or a collapsible pole, but they are a minimum.  The antenna will
perform better than a helical or center-loaded whip, but it is pretty much a
ground plane with a poor radial and antenna literature suggests that many
radials are needed for efficiency in verticals over ground.  Some time, I
want to try more wire on my end-fed field antenna, possibly 80 to 100 feet
with several 16 foot radials, or, a radial for each band.  That would be
more effective than 28 feet/1 radial.  

I'd also like to try a doublet of 60 to 88 feet; fed with a parallel
feedline of made the same "stealth" wire as the antenna (no heavy ladder
lines).  The doublet would be more cumbersome (requiring one central support
or else supports at each end).  The antenna plus feeder length would be
chosen to provide a relatively tame feedpoint impedance and reactance on the
three bands; 40/30/20M.

More research is needed on end- and center-fed (no coax) wire antenna
lengths for the KX1   (and the KX3)

I agree, leave the co-ax at home!



73
Jay
W6CJ







-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Pat
Ring
Sent: Sunday, April 19, 2015 15:09
To: elecraft at mailman.qth.net
Subject: [Elecraft] KX1: requesting recommended wire antenna lengths advice

Hello.  I researched this, eh, pretty thoroughly, but I keep running into a
little problem with the recommended lengths for direct-fed antennas.  The
KXATU guides recommend a 24'-28' radiator and a 1/8 wave
ground/counterpoise, but I have seen 28' and 41' recommended as well (some
with recommended radials and some without).  The 24' wire tuned up fine on
20m and 30m, around 1.2:1, but I can't get an KX1ATU lower than about 8.9
SWR on 40.  Am I missing something obvious, or should I continue to
experiment?  I've only tried that ATU about three times on 40M because that
SWR seems pretty high to me and has to be tough on the kit.  I am reluctant
to continue to try anything in this range now.  I don't really want to take
coax on the road with me, and 20m and 30m are ok, but I would like to
participate in the 4sQRP on 40m when I am on the road this week.  I would
appreciate your advice.  Thanks.  Pat NQ0N
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