K2 #4487 up and running on CW but SSB...

[Tom Rune Breivold]

My K2 works great both on RX and TX in CW. Also RX on SSB is splendid, but
my SSB TX sounds like a built in unfiltered switchmode supply. During
alignment I can listen to my voice in the headphones and it sounds ok. But
during "normal" mode in SSB TX has a whining sound. It increases at the
upper part of the band and decreases I frequency at the lower portions of
the band. I have tried running my K2 from a car battery - but the sounds are
still there. I have checked all components for misplacements and values and
are correct. Weher do I look?

 

Sincerely

LA6VNA

Tom Rune Breivold

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[Don Wilhelm-3]

Tom,

Just a few guesses here:

The first thing I would suspect is RF feedback into the audio section.  If
you did not ground the microphone jack, that would be the first step to
take.
Second step is to check the antenna situation.  Could RF from the antenna
(and/or the feedline) be bringing RF into the shack?  The best way to tell
is to connect a dummy load to the K2 and listen with another receiver - if
the problem goes away, you can be certain it is caused by RF feedback.

The second thing to suspect is magnetic coupling to something (power supply,
computer monitor, etc).  Such magnetic coupling will modulate the BFO - and
may or may not be noticable on received signals - but can show up when
transmitting.

If you are certain the problem is NOT caused by RF feedback, then check out
the audio section of the KSB2.  There are not a lot of components involved
since most of the circuitry is inside the Speech compressor chip.  A 'scope
would be helpful in chasing gremlins such as you describe - Check the inputs
to the balanced modulator and the RF output to see whether the problem is
coming from the audio or the RF portions of the K2.

73,
Don W3FPR

----- Original Message -----

> My K2 works great both on RX and TX in CW. Also RX on SSB is splendid, but
> my SSB TX sounds like a built in unfiltered switchmode supply. During
> alignment I can listen to my voice in the headphones and it sounds ok. But
> during "normal" mode in SSB TX has a whining sound. It increases at the
> upper part of the band and decreases I frequency at the lower portions of
> the band. I have tried running my K2 from a car battery - but the sounds
> are
> still there. I have checked all components for misplacements and values
> and
> are correct. Weher do I look?
>

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