Posted by
Mike Scott-7 on
Feb 20, 2009; 6:49pm
URL: http://elecraft.85.s1.nabble.com/PSK31-DM780-tp2354428p2360676.html
>Jim Brow wrote: That's harmonic or intermod distortion. Something in your
audio chain is being overdriven. Could be the sound card. Or if it's an
older K3, it could be the radio. Older versions of the K3 produce a LOT of
audio distortion at the Line Out for settings of Line Out gain greater than
about 10. Distortion starts showing up weakly with a setting around 5, and
is bonkers up around 50.
Jim, your K3 and mine seem a bit different. Before I put the audio
modification in my K3 [ser 508] I would see obvious IMD on the DM780
waterfall or Spectrumlab with Line Out set anywhere above 3, 10 was
problematic. Even at 3 I could see harmonics of S9 tones.
After the modification I run Line Out about 10 and see I see slight IMD
above band noise 60-70dB below the carrier tone, passable.
I have played with sound card gain to try and make sure that the sound card
is not being over driven but I have to admit that I don't really know how to
distribute the gain between the sound card and the K3 Line Out. DM780 has a
soundcard Receive Signal Level; I run it in the lower 25% of the scale and
seem to see nice traces.
Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
K3-100 #508/ KX1 #1311
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