Distortion

[Hans Bonnesen]

K2 Audio Distortion.

My otherwise flawless K2 # 7359  is found to have
serious audio distortion problems on received and transmitted signals on 40 meter.
The problem appears as soon as I go above 7171 kHz. On 7182 the problem makes SSB contacts impossible
Lower frequencies do not suffer. Why ?
I still haven’t checked the problem on other bands.

73 de
OZ5RB, Hans

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[Sverre Holm (LA3ZA)]

Hi Hans

You seem to have a known problem - with a known fix: "Weird behavior around 7185 kHz." It is due to  interaction between the VFO and the PLL reference oscillator. Search for '7185' in my list http://la3za.blogspot.no/p/la3za-unofficial-guide-to-elecraft-k2_5502.html and you will find some links that will help you.

[Don Wilhelm-4]

Hans,

That sounds like the old WAOF (Weird At One Frequency) problem. That is
the region where the PLL oscillator and VFO frequencies "cross paths"
near 7185 kHz.  See http://www.elecraft.com/Apps/Alert11_WAOF.html.  
Note that this alert refers to older version A K2s, you will not find
C70 on your board.

If this is your problem, the audio signals will sound rather like they
are 'under water'  If you have something different, then ask again.

With a new K2 layout, that seldom happens, so check to be certain D16 is
mounted flush with the board.
In addition, the components mounted on the bottom of U4 (C88, RFC15 and
C91) should have leads as short as possible - make certain they are
connected to the correct pins.
You may need to trim all leads in the vicinity of U4 so there is nothing
that would act as an 'antenna'.

73,
Don W3FPR

On 3/26/2014 1:44 PM, Hans Elfelt Bonnesen wrote:
> K2 Audio Distortion.
>
> My otherwise flawless K2 # 7359  is found to have
> serious audio distortion problems on received and transmitted signals on 40 meter.
> The problem appears as soon as I go above 7171 kHz. On 7182 the problem makes SSB contacts impossible
> Lower frequencies do not suffer. Why ?
> I still haven’t checked the problem on other bands.
>
>

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[Phil Wheeler-2]

Nice list you have, Sverre. My K2 (#380) didn't
suffer from this malaise (I tested it as
specified) but I've done most all the others. Most
recent was the AF pot mod: No parts, but fussy
work on the three main boards -- and well worth
the effort!

73, Phil W7ox

On 3/26/14, 11:48 AM, Sverre Holm (LA3ZA) wrote:

> Hi Hans
>
> You seem to have a known problem - with a known fix: "Weird behavior around
> 7185 kHz." It is due to  interaction between the VFO and the PLL reference
> oscillator. Search for '7185' in my list
> http://la3za.blogspot.no/p/la3za-unofficial-guide-to-elecraft-k2_5502.html
> <http://la3za.blogspot.no/p/la3za-unofficial-guide-to-elecraft-k2_5502.html>
> and you will find some links that will help you.
>
>
>
>
>
> -----
> Sverre, LA3ZA
>
> K2 #2198, K3 #3391,
> LA3ZA Blog: http://la3za.blogspot.com,
> LA3ZA Unofficial Guide to K2 modifications: http://la3za.blogspot.com/p/la3za-unofficial-guide-to-elecraft-k2.html
>
>

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[Sverre Holm (LA3ZA)]

Phil Wheeler-2 wrote

Nice list you have, Sverre.

Thanks! Since August last year I have updated the list (link in my signature field) and added several photos to make it easier to navigate.