KX-1 antenna question

[Lloyd Lachow]

posted for Eric:

-------- Original Message --------
Subject: KX-1 antenna question
Date: Thu, 28 Jul 2005 09:30:42 -0400
From: Eric Ward <[hidden email]>
To: [hidden email]
CC: [hidden email]
References:
<[hidden email]>



So I have settled on a 26-28' wire with a 16'
counterpoise.  I found
that a 24' wire working against a 16' 'poise would not

always load up on
40m--it needs to be at an obtuse angle to the plane of

the counterpoise
to tune well on 40m with the internal tuner.  In
contrast, the 26-28'
piece will tune to <2:1 on 40m even if strung
carelessly over doors,
picture frames, or whatever else is available (e.g. in

a hotel room with
windows that don't open).  20 and 30m seem to tune
fine with the 24'/16'
ant, even if suboptimally deployed.

Question: Assuming both tune up about as well, do you
think the 24' ant
with a longer (33') counterpoise will radiate better
on 40m than a
26-28' ant with a 16' 'poise?  I realize there are
many uncontrolled
variables involved, but maybe it is simpler than I
think?

Eric N0HHS KX1 #670


               
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[Terry Conboy]

At 07:13 AM 2005-07-28, Lloyd Lachow wrote:

>Posted for Eric N0HHS KX1 #670 <[hidden email]>:
>
>So I have settled on a 26-28' wire with a 16' counterpoise.  I found
>that a 24' wire working against a 16' 'poise would not always load up on
>40m--it needs to be at an obtuse angle to the plane of the counterpoise
>to tune well on 40m with the internal tuner.
>
>In contrast, the 26-28' piece will tune to <2:1 on 40m even if strung
>carelessly over doors, picture frames, or whatever else is available (e.g. in
>a hotel room with windows that don't open).
>
>20 and 30m seem to tune fine with the 24'/16' ant, even if
>suboptimally deployed.
>
>Question: Assuming both tune up about as well, do you think the 24'
>ant with a longer (33') counterpoise will radiate better on 40m than
>a 26-28' ant with a 16' 'poise?  I realize there are many
>uncontrolled variables involved, but maybe it is simpler than I think?

The feedpoint capacitive reactance with 27-foot antenna wire and a
single 16-foot counterpoise wire is quite high at 7 MHz, on the order
of 680 ohms, depending on proximity to ground, etc.

You might want to try adding a second 16 foot counterpoise wire,
separated from the first by 45 degrees or more.  This causes the
reactance at the feedpoint to drop to around 450 ohms, which should
make for an easier match (and less loss in the KX1 tuner).

In my EZNEC model, with the two 16-foot counterpoise wires 2 feet
above average ground, the overall efficiency rises by about 1 dB, as
well.  This configuration appears to produce relatively good
efficiency on 20 & 30m, too.

Using a single 24 foot counterpoise wire might be a workable
compromise.  The 40m reactance is around 420 ohms.  However, the 20m
impedance rises from 225+j523 to 289+j977 when going from a 16 foot
to 24 foot counterpoise, so some experimentation might be required to
see how the KX1 handles this.

A single 33-foot counterpoise wire is about 1/2 wl on 20m, so it
might make matching there difficult due to the resulting high
impedance.  The overall losses increase by around 3 dB, too.  On 40m,
my model also shows slightly lower efficiency (-1 dB or so).  This
might seem odd, but since the counterpoise wire is longer than the
"antenna" wire and it carries at least as much current, there is a
tendency to have more radiation from the counterpoise than the
"antenna" proper.  Since the counterpoise is probably closer to
ground, etc., the losses may be somewhat higher and the pattern degraded.

(Note that using two 33-foot counterpoise wires, 180 degrees apart is
a different story on 40m.  This is a common "elevated radial"
configuration and the efficiency is much better since the radiation
from the two wires tends to cancel in the far field.  Of course, the
impedance would still be high on 20m.)

73,
Terry N6RY

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[Stuart Rohre]

Terry, you want the part of the antenna in the air to be the longer piece.
And the highest piece for best results.  Any antenna configuration that
bends the antenna back upon itself will detract from the overall working as
an antenna, even if it makes the "SWR" look "good".  Remember, a light bulb
may give you low SWR but will not work many stations.
Same as the dummy load is excellent 1:1 SWR for it is 50 ohms; but NO DX
antenna!

Stuart
K5KVH



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