I played with line out settings today to determine for my soundcard-K3 setup
what an optimum line out setting might be. I think of optimum as that
setting that produces adequate speckling on a waterfall display with minimum
harmonic distortion.
My K3 serial 508 has all of the audio modifications that I am aware of. I
can remember conducting a study like this prior to modifications
unfortunately I can not find my old data.
Bottom line I have my line out set at 3 now. This gives good copy on PSK
signals, good speckling on a waterfall and maximum signal-to-3rd-harmonic
ratio.
Spot pitch = 500, CW signal centered, 3rd harmonic well outside of roofing
filter as well as 50 Hz IF filter. The only way for the 3rd harmonic to be
seen is if it is created in the analog post digital audio stages. For PSK
copy I would be using wider filters but much wider would mask the 3rd
harmonic measurements which I wanted to be well beyond the processing pass
band.
Using Spectrogram for signal measurement and Ham Radio Deluxe-Digital Master
780 for PSK copy I took some data below. At line out set at 3 I found
maximum base signal to 3rd harmonic ratio. I find this is pretty good at the
lower line out settings and up to 15 dB worse at significantly higher
settings. I would guess that most could live with the higher settings if the
sound card needs it.
IF BW = 50 Hz
Roofing Filter BW = 500 Hz
Line Reference 3rd Delta
Out dB Harmonic 3rd
0 -68.6 noise limited
1 -55 noise limited
2 -41.7 -113 71.3
3 -38.2 -111 72.8
4 -35.8 -107 71.2
5 -33.5 -101 67.5
10 -27.8 -87.5 59.7
15 -24.5 -82 57.5
20 -21.5 -80.3 58.8
25 -19.4 -78.5 59.1
30 -18.1 -75.8 57.7
50 -13.7 -72.1 58.4
100 -7.7 -67.8 60.1
Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1 #1311
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