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Default AGC value. [fixed in v1.441]

Hi John,

Somewhere along the way during new versions the default AGC value seems to have changed from whatever it was (-90 or -100dB ?) to -130dB.

The net result is that the AGC on most KiWi's is now less effective and the noise floor excessively high, unless the user manually alters the value back to something more sensible.

Regards,

Martin - G8JNJ

Comments

  • I did that because the NDB'ers complained the Kiwi had no sensitivity on weak signals using super-narrow passbands (on the order of 10 Hz). And with an AGC threshold of -100 dB this is true -- spend some time listening using those conditions. Things improve greatly with the threshold reduced.

    Maybe the solution is to change the default back to -100 but apply an automatic reduction for narrow bandwidths.
  • Hi John,

    Ah OK, so that explains what's happened.

    A couple of my users have complained that when listening to HF airband traffic the background noise is fatiguing and I had suggested they try altering the AGC threshold, but I hadn't realised that you had altered the default threshold value. This is also why I recently raised the squelch issue again.

    Using a typical USB bandwidth of 2.8KHz and no antenna connected the background noise just starts to disappear with an AGC threshold setting of somewhere around -110dB, but with an antenna connected the background noise starts to reduce at around -100dB and with my antenna it is just about right at around -90dB.

    With narrow CW and 60Hz BW with no antenna connected the noise starts to reduce at around -125dB, and with an antenna connected (for me) it's around -110dB.

    So maybe the AGC threshold point has to vary in order to track the noise floor in the RX bandwidth that has been set ?

    I think it's an easy mathematical relationship, as the above example demonstrates 2.8KHz / 60Hz equates to approximately 17dB.

    At the moment the default of -130dB means that the background noise level is higher than it needs to be for the majority of my users.

    What do others think ?

    Regards,

    Martin - G8JNJ
  • I like the agc by BW idea
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