[Elecraft] K3S USB audio questions

[Richard Lamont]

On 05/11/16 18:13, ab2tc wrote:
[
>>> 4. When listening to SSB audio at S9+, with slow AGC, the output level
>>> via this interface seems to be -22 dBFS true peak. Why is it throwing
>>> away three bits of resolution? Or is this amount of headroom
>>> necessary/useful?

> The audio level seen by, say a recording program on the PC depends on the
> LINE OUT setting on the K3. I left that as the default, 10, and used the
> Windows mixer to adjust the level. My audio is now reading  approximately
> -6dB below clipping which is probably a little high, but I have set my AGC
> SLP to the flattest possible setting (highest number). If you prefer a
> considerable slope on the AGC curve above threshold, you will need a lower
> LINE OUT setting. Remember that even when throwing away 3 bits, you still
> have far more resolution than you can use with an HF receiver.

Consider JT65+JT9. There might be 30 or more signals within a 4 kHz
band, with widely varying levels. If they're all at the same level, then
each signal will be about 30 dB below the sum of the signals. If the
signal you want is 30 dB weaker than the others, then it will be 60 dB
below the sum.

The data sheet shows the ADC has an SNR of 89 dB and THD+N of 0.01%
(i.e. -80 dB).

If the sum of the signals is peaking to -22 dBFS true peak, than that
weak JT65/JT9 signal is going to be at -82 dBFS - close to the ADC noise
floor. Maybe getting at least some of those three bits back could make
quite a difference.


-- 
Richard Lamont G4DYA
<richard at lamont.me.uk>