[Elecraft] We need to develop the Ideal Antenna!

[Don Wilhelm]

  Bob,

Actually, a properly functioning KX1 has an MDS of better than -130 dBm, 
so it actually is a sensitive receiver.

Some like the Carolina Windom, but I don't like any unbalanced antennas, 
and have a high preference for center fed antennas, they are easier to 
tame, and if the feedline leaves the antenna at right angles from the 
center, seldom do "RF-in-the-shack" problems emerge.

The KXAT1 has a more limited range on 80 meters than the other bands 
just because the total inductance and capacitance is limited - only 3 
choices of each.

I would suggest a trap antenna with traps for 40 and 20 meters.  Feed it 
with balanced feedline cut a half wavelength (or multiple) on 80 meters 
- the tuner should be able to match it on 30 meters and the half 
wavelength of feedline on 80 meters should present a feedpoint impedance 
close to that at the antenna center (50 to 75 ohms) for 80, 40, and 20 
(assuming the traps are used).
I have not actually built such an antenna, but the theory says it should 
work just fine.  Keep the balanced feedline supported along its entire 
length and don't forget that there is a velocity factor to consider when 
determining a half wavelength - if you cannot do that, add a trap for 30 
meters and feed it with any length of coax.  Coaxial traps are not 
difficult to build, and for QRP use, can even use RG174 on a piece of 
1/2 inch PVC for a form.  Doug DeMaw (SK) W1FB had information on 
building traps like that in QST a very long time ago (try in the 
1980s).  Also see the W1FB Antenna Notebook and/or the article in QST 
for Decenber 1984 page 37 by N4UU.  Gary o'Neil N3GO also has some good 
information about coaxial traps on the web (use Google).

I realize that a 135 foot long antenna is not "easy to deploy", so I 
would suggest an alternative - build a coax fed trap antenna for 40, 30 
and 20 meters (traps for 30 and 20), and carry along 2 33 foot lengths 
of wire - insulators on one end and an alligator clip on the other - 
when you want to operate 80 meters, add the wires to each end of the 
radiator.  You could carry that concept a bit further, and build the 
antenna for 20 meters with no traps and then add a set wires for use on 
30 meters, another set of wires for 40, and yet another set for 80.  
clip on the wires for whichever band you want to operate.

That is my nickel's worth.

73,
Don W3FPR

On 5/13/2011 1:31 PM, AB5N wrote:
> Hi Guys-
>
> Well, I'm in week two of enjoyment with my new KX-1. I did have a few
> problems in assembling, but
> that is history.
>
> This little rig has a simple receiver which has only half the sensitivity of
> a usual radio. As well, we are dealing
> with 3-4 watts TX out max. We have to have an excellent antenna. I've tried
> the suggested 25 ft. long wire
> with radials. Ah, it's not good enough. I even got some strange RX-feedback
> internally at some frequencies using it. I believe the criteria for an
> excellent antenna will be as follows:
>
> 1. Will match up well using the internal tuner on all four bands.
>
> 2. Has enough metal in the air to provide adequate microvolts to the RX - to
> make it function well without
> being overloaded.
>
> 3. Provides some gain - or at least a clean predictable pattern
>
> 4. Is light, compact and easy to deploy.
>
> My inkling is that a normal Carolina Windom may be the thing. I'll work on
> developing a micro-QRP version.
>
> What doesn't work?
>
> Classic G5RV (102 Ft) - will not load on any band with tuner.
> Offset-Zepp fed with Coax (75'x25')
>
> What say guys? Anybody have superb luck with an antenna yet?
>
> Bob-AB5N
>