[Elecraft] KXAT1 with dipole

[Dan Presley]

>
>-------------------------------------------------------
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>You should not have had any trouble with a center fed dipole, Dan. The issue
>with the KX1 ATU, as with any ATU, is impedance extremes. Because of the
>limited number of inductors and capacitors that could be fitted into the
>tiny space available in the KX1, it has a more limited tuning range than any
>of the other Elecraft tuners.
>
>The end of a dipole presents a very high impedance, possibly in the
>thousands of ohms. At the other extreme, a very short antenna will present a
>very low impedance, often less than an ohm. Actually, end-fed short antennas
>often tune up more easily because they are working against ground and
>typically Hams have lousy RF grounds <G>. Even with several "radials" the
>ground impedance will likely be in the tens or, more likely, the hundreds of
>ohms. That's in series with the antenna so what the tuner is matching is a
>total impedance of perhaps a hundred ohms or more. The fraction of an ohm
>that the antenna represents is just part of the total. It's also why such
>antennas have a very, very low efficiency: often less than a few percent.
>
>In your case, I'd suspect you had an unlucky length of feed line. Unless the
>SWR is truly 1:1 on that feeder, something that is almost never achieved in
>practice, the feed line acts like a random impedance transformer. I suspect
>you got unlucky and the combination of the effect of surrounding objects,
>antenna length, feeder impedance and feeder length all added up to an
>impedance the KX1 ATU couldn't handle. Adding a few feet of feed line will
>usually fix that.
>
>Another possibility is a short or open, as you suggested.
>
>Ron AC7AC
>
Thanks,Ron and all of those who replied for the good advice. I'm 
betting you're right on the money as far as feedline length. I'll put 
the antenna back up and check it with my dipper to see how it reads, 
and also with the rig in 'cal' (tuner bypass) mode. That'll tell me 
also if there's a short somewhere too. I tend to forget about the 
feedline length as I often just use an endfed wire from the KX1, or 
at home I use ladder line. I know this can still happen with ladder 
line, but perhaps less of an issue than coax.Besides, the ol' Johnson 
matchbox is pretty forgiving:)
-- 
Dan Presley-N7CQR-Portland, Or QRP-L #502 ARS #71
n7cqr at arrl.net