Re: K3 Audio Feedback

Posted by Jim Brown-10 on Jan 18, 2010; 5:18am
URL: http://elecraft.85.s1.nabble.com/K3-Audio-Feedback-tp4411727p4411862.html

On Mon, 18 Jan 2010 04:21:16 +0000, Jim Harris wrote:

>While phone contesting yesterday I found there is audio feedback
>from headphones/external speakers through the microphone without
>the PTT being pressed.

The problem may be related to the sound card in your computer.
Depending on settings in your logging software and the computer
sound card mixers, the sound card may be the feedback path.

There are two "mixers" in a typical sound card, one for
"recording" that feeds audio to the computer to be handled by
software, and another for "playback" that controls sound fed by
the sound card to external equipment (like the K3).

When you feed audio to the K3 (either recorded messages or your
live mic), you are using the Playback mixer. The catch is that
there's an input on this mixer for a microphone, and most laptops
have a mic built into their case. When they do, that mic is on by
default. There's usually a switch (in the mixer) to turn it off
and turn on a mic that plugs into the mic jack. Either the
internal mic or an external mic plugged in can be part of the
feedback path. To determine if its the internal mic, bang on the
computer case and see if you "hear" it in your K3. I often run
into this when setting up my IBM laptops for RTTY -- the input to
the recording sound card is that internal mic rather than the
wired input from the K3, so decoding "sort of" works, but not very
well. :)  

So I suggest that you study YOUR setup, think about the computer
sound card signal flow, and study your mixer settings. Also, keep
the mixers open and viewable on your screen while the logger is
doing its thing -- some loggers (N1MM, for example) actively
controls the mixers to do recording on the fly of new messages,
and to switch a mic plugged into the computer to one radio or the
other for radio for SO2R.

73,

Jim K9YC



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