[Elecraft] K3: KPA100 Squeal

[Guy Olinger K2AV]

Hi Geoff, below...

On Thu, Jun 30, 2011 at 9:24 AM, Geoff Wolf AB3LS
<liltechdude13 at gmail.com> wrote:
> And, for even more information, I analyzed the audio that I recorded and the
> squeal is right around 12Khz. It peaks at -48dB (louder than the QSK relay
> clicking)
>
> http://imgur.com/V8o5t - image of the analysis
>
> AB3LS

With your image I realize I had been making some assumptions.  I need
to fill in some details...

Are you listening to the audio in earphones or are you hearing it in
the free air.  I had been assuming listening with your ears only in
free air to miscellaneous sound in the neighborhood of the K3.

*ASSUMING* open air, what did you use to record the sound levels?
Would point out that the recordings don't get the sound to me,
possibly because the program devices you are using won't pass 12 kHz.
It would we difficult for me in any event as my hearing can barely
hear anything at that frequency.  This as opposed to MY college days,
when I could hear 15 kHz made by the old analog TV set sweep
generator.

There are a lot of us in that highs reduced hearing state, so many
will tell you they don't hear a 12 kHz squeal.  And they don't,
whether or not it is there.  Likewise, any clicking that is made from
a 12 kHz basis.

In any event, I doubt it is being transmitted (have someone check up
and down 12 kHz from you sending) because a spectral purity issue
would have been beaten to death here (no shortage whatsoever of
beaters-to-death on the reflector).  There WERE some spectral purity
issues early on that needed physical mods to boards and are standard
in the mfr version for a long time now.

The puzzler is hearing it when the KPA is set to "not installed" in
the config menu.

This leads me to wonder if you have that spur from your power supply.
You ARE talking about a level that would pass spec.  It could be that
there is something in the KPA that is mechanically resonant to 12 kHz
and will respond to it if it is on the power.  You will need to put an
audio scope on the power supply.   In any event, you need to rule out
having stuff on your DC lead from your power supply.

73, Guy.