K3 Audio Feedback

[Jim HaRRIS]

Hi folks,

While phone contesting yesterday I found there is audio feedback from headphones/external speakers through the microphone without the PTT being pressed.  Monitor level was initially set at about 15.  I was using a Heil BM-10ic headphone through the front panel with bias turned on.  They have tiny ear pads that could easily let an amount of noise slip past to the microphone.  The audio line out on my K3 back panel goes to a computer which has garden variety speakers hooked to it's audio out.

On the radio I had the AF control turned most of the way up and was riding the RF (IF) gain.  NR was on with a setting of F1-2.  I found that when the RF gain was turned up something like half way or more (depending on signal level) the audio level would creep up as though AGC was pumping.  If the gain was further increased the characteristic howl of feedback resulted.  Remember all this was occurring without PTT (no PTT light).  I would have thought the microphone would be dead without PTT.

I turned down the monitor to 8 and the feedback was not as much but was still present.  Finally I moved the volume control slider for the computer speakers to the bottom and that eliminated the feedback.

I'm very surprised to find a microphone connected to the K3 is live and that the audio is being feed to the audio outputs without the PTT being pressed resulting in the described feedback.  That is disappointing because it limits the ways that I can use my radio.  I'm wondering if this may be the source of some noise comments here on the reflector.  Does anyone else have any experience with this or any constructive comments?

Have a good day and 73.

Jim, W0EM


     
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[N5GE]

On Mon, 18 Jan 2010 04:21:16 +0000, Jim Harris <[hidden email]> wrote:

Did You check your VOX to make sure it was off?
Tom, N5GE

[hidden email]
K3 #806 with SUB RX, K3 #1055, PR6,
XV144, XV432, KRC2,
W1, 2 W2's and other small kits

1 K144XV on order

http://www.n5ge.com
http://www.swotrc.net

>
>Hi folks,
>
>While phone contesting yesterday I found there is audio feedback from headphones/external speakers through the microphone without the PTT being pressed.  Monitor level was initially set at about 15.  I was using a Heil BM-10ic headphone through the front panel with bias turned on.  They have tiny ear pads that could easily let an amount of noise slip past to the microphone.  The audio line out on my K3 back panel goes to a computer which has garden variety speakers hooked to it's audio out.
>
>On the radio I had the AF control turned most of the way up and was riding the RF (IF) gain.  NR was on with a setting of F1-2.  I found that when the RF gain was turned up something like half way or more (depending on signal level) the audio level would creep up as though AGC was pumping.  If the gain was further increased the characteristic howl of feedback resulted.  Remember all this was occurring without PTT (no PTT light).  I would have thought the microphone would be dead without PTT.
>
>I turned down the monitor to 8 and the feedback was not as much but was still present.  Finally I moved the volume control slider for the computer speakers to the bottom and that eliminated the feedback.
>
>I'm very surprised to find a microphone connected to the K3 is live and that the audio is being feed to the audio outputs without the PTT being pressed resulting in the described feedback.  That is disappointing because it limits the ways that I can use my radio.  I'm wondering if this may be the source of some noise comments here on the reflector.  Does anyone else have any experience with this or any constructive comments?
>
>Have a good day and 73.
>
>Jim, W0EM
>
>
>    
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Jim Brown-10]

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



______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html