[Elecraft] KXAT1 with dipole

[Karl Larsen]

    Guys, my money is on the connector on the feedline. It must have a 
short developed since the last time you used it. Or the short might be 
at the antenna feed point.

    The feed line length is just not a factor even when there is RF on 
the shield, and there is some.

    The MFJ Antenna Analyser will find the problem. I love mine.

73 Karl K5DI



Dan Presley wrote:
>>
>> -------------------------------------------------------
>>
>> 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:)