[Elecraft] KAT500 TUNER WOES

[Don Wilhelm]

David,

What have you changed on that antenna system since it last "worked"?
The length of the antenna is only part of the story, because the length 
of the feedline is also an important parameter.  If you changed the 
feedline, that can make the difference between working and not working.
The length consideration should be the feedline length plus 1/2 of the 
antenna length.  If that comes close to a 1/2 wavelength, the antenna 
will be hard to feed since it represents a high impedance to the tuner.  
Likewise, if the feedline plus half antenna is an odd multiple of 1/4 
wavelength, it will present a very low impedance to the tuner which can 
be difficult to match.

Adding (or subtracting) a bit of feedline - add or subtract 1/8 
wavelength at the problem frequency - can make all the difference 
between obtaining a match or not.

73,
Don W3FPR

On 5/19/2014 9:26 PM, David Inger wrote:
> I have a fairly early KAT500 tuner  (#275).  I am using it to tune several
> antennas.  Recently it has stopped finding acceptable matches to a
> ladderline-fed 110 ft. dipole.   This problem is only on 40-meters.  The SWR
> anywhere in that band is around 8:1.  The tuner works great on all other
> bands (well, not so much on 160, but that's the antenna's problem).  I also
> have a 43-ft vertical and the tuner matches fine on that antenna.  I
> replaced all intervening coax jumpers and even the 1:1 current balun at the
> transition of the ladderline to the coax in the shack.  None of the above
> help.
>
>   
>
> Interestingly, when I bypass the KAT500 and enable the internal tuner in the
> K3, everything works fine, including matching 40-meters.  I have also done a
> reset using the KAT500 utility program; still no help.
>
>