[Elecraft] Strange K3 & KPA500 Issues fixed with a longer coax cable?

[Milverton M. Swire via Elecraft]

Jim, RFI is not the issue here.What is happening is a matter of " Inductance " 
By adjusting the length of the Jumper, the Impedance is adjusted accordingly. 
((((73)))) Milverton. 

      From: James kvochick <jameskvochick at me.com>
 To: "N2TK, Tony" <tony.kaz at verizon.net> 
Cc: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net> 
 Sent: Wednesday, November 19, 2014 7:19 AM
 Subject: Re: [Elecraft] Strange K3 & KPA500 Issues fixed with a longer coax cable?
   
We tried all the normal "common mode" tricks, but the feedline length appeared to be the most effective.

Jim K8JK


Sent from my iPad

> On Nov 19, 2014, at 7:32 AM, N2TK, Tony <tony.kaz at verizon.net> wrote:
> 
> I had a similar problem many years ago with an L-4B amp. 
> I wonder if adding ferrite to the coax would solve this problem?
> GL
> N2TK, Tony
> 
> -----Original Message-----
> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim
> Kvochick
> Sent: Tuesday, November 18, 2014 9:16 PM
> To: elecraft at mailman.qth.net
> Cc: kvo at att.net
> Subject: [Elecraft] Strange K3 & KPA500 Issues fixed with a longer coax
> cable?
> 
> I've stumbled into a strange problem.
> 
> I have 4 friends with similar K3 stations to my own; K3 >>> KPA500 >>>
> KAT500.  The stations are powered with similar power sources.
> 
> One station sounds fine, works great.  The other 4 had strange issues that
> manifested themselves as audio distortion when running the amplifier.  After
> looking all over for RF and grounding issues, we swapped the coax cable from
> the K3 to the amplifier, with a longer cable (about 6 to 7 feet - largely
> because that was the only free cable we had handy).
> 
> Making the cable from the K3 to the amplifier longer eliminated the issue.
> putting the cable back brought the problem back.  Making a new short cable
> still left us with audio distortion.  The only thing that seemed to solve
> the issue in all 4 cases was making the K3 to amplifier cable longer. 
> 
> This got me to investigate my own station.  It turns out that the cable I
> used between the amplifier and the radio was about 6 feet long.  Swapping
> this cable for a shorter length brought about audio distortion symptoms.
> 
> Does anyone have any thoughts about this?
> 
> Cheers
> 
> Jim K8JK
> 
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