[Elecraft] PSK audio problems with K2

[Don Wilhelm]

Stephen,

I believe you may be overdriving the microphone input of the K2.

Do you have any attenuation between your soundcard output and the K2 
microphone input?  On the output (K2) side of the transformer connect a 
series resistor about 10k in value and a 1k across the wires to the 
microphone.  That will drop the soundcard level down to about 1/10 of 
the soundcard output and keep from overdriving the microphone input.  
Reduce the 1k resistor if the soundcard still overloads the mic input of 
the K2.

73,
Don W3FPR

Stephen Prior wrote:
> Can anyone shed any light on this please?
>
> I have connected tx and rx audio from/to the computer via isolation
> transformers on both audio in and out.  Rx works fine.
>
> However, I have hit a problem trying to get acceptable transmit audio
> quality.  I have the K2 stripped back to 10W at the moment so am not using
> my external KPA100 in order to remove that from the equation.  I am feeding
> the audio from the computer via the isolating transformer straight to the
> microphone header with the microphone removed.  I have turned the compressor
> off in all modes.  I have no ALC showing and have tried the power control in
> various positions.  The audio is extremely rough with various artifacts
> spreading widely above and below the tx frequency.
>
> I have the K2 feeding into a 100W Bird dummy load.  I have listened both
> with my K1 with a few inches of wire as an antenna and my TS-480HX in the
> car parked outside.  Same grotty received audio.
>
> I have checked the carrier balance on the ssb board.  Although still audible
> in the K1¹s receiver I have minimised it for usb and lsb.  I note that I can
> eliminate it almost altogether for lsb, but then the level at usb is high.
> So it¹s a compromise as I have read it would be.
>
> I have tried both my desktop pc (a mac) and my Dell laptop (XP) - no
> difference.  I have listened directly to the audio output from the computers
> ­ it sounds right.
>
> I must have used psk31 on a dozen or more radios in the last ten years or
> so, but never hit this severe a problem before.  Listening to my ssb speech
> via the HM12 microphone, it doesn¹t sound great, but yet I am using the K1
> to listen to it with so that¹s not too surprising.  I don¹t use ssb at all
> except mobile, so have had no operating experience of the K2 in this mode.
>
> I am wondering if the problem lies deeper somewhere.  I have googled, but
> hit nothing useful.
>
> Any thoughts would be much appreciated
>
> Thanks and 73,
>
> Stephen G4SJP
>
>
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