[Elecraft] KAT500 TUNER WOES

[Doug Person via Elecraft]

Also, consider making sure you have the latest firmware updates.  I have 
also experienced the situation where the K3 internal tuner will tune my 
200' ladder-line fed doublet but the KAT500 will not.  I'm hoping that 
subsequent updates will improve the KAT500's algorithms.
73, Doug -- K0DXV

On 5/19/2014 8:50 PM, Don Wilhelm wrote:
> 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.
>>
>>
>
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