Posted by
Jim Brown-10 on
Sep 07, 2010; 6:30pm
URL: http://elecraft.85.s1.nabble.com/Odd-audio-feedback-problem-tp5507365p5507677.html
On Tue, 7 Sep 2010 10:01:26 -0700, George A. Thornton wrote:
>I also tried silencing
>the computer microphone, presuming that the microphone was picking up
>audio from the spoken Tx and feeding it back somehow through one of the
>sound cards.
Look at this again. This is a very common problem, usually caused by a
piece of software switching the Windows Mixer in ways that it thinks you
want. Remember that there are TWO Windows Mixers -- one for record, and
the second for playback.
There is another mechanism that sounds just like RF feedback but is
actually modulation of the DC voltage as a result of IR drop when
transmitting SSB. If the V- bus in the power supply is bonded to the
chassis, that modulation, which sounds just like SSB on an AM RX, gets
added to the TX audio. W8JI was the first to alert us to this problem, and
I have done testing to duplicate it in my shack. This problem can also
happen if you get power for accessories direct from the power supply and
then connect them to the rig.
73, Jim K9YC
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