Jack I have seen postings on the main reflector recommending settings as low as 3 to avoid distortion products that are being attributed to transformer distortion. This did not really make sense to me, especially at such low levels where consumer sound cards tend to get non-linear and nasty.
I took a look at the specifications for the TTC-108 audio transformer used in the line out of the K3 Nominally it's specified as having an operating level of -45dBm to +7dBm THD is specified at 0.5% @0dBm 300Hz to 3.5 Khz @ 0dBm this would make the transformer related harmonics worst case at -46dB relative to the fundamental I did some measurements with an s9 CW signal zero beat at various pitch settings I used an old copy of SMAART pro that I have from my Sound engineering days. the sound card is a delta44 Lin = 100 Pitch 300 pitch 550 pitch 800 DR3 47.3dB 51.4dB 54dB Lin = 50 Pitch 300 Pitch 550 Pitch 800 DR3 43.1dB 47.6dB 50.6dB Lin = 10 Pitch 300 Pitch 550 Pitch 800 DR3 35dB 39.7dB 43.1dB Lin = 5 Pitch 300 Pitch 550 Pitch 800 DR3 31.9dB 37.7dB 42.7dB Lin = 3 Pitch 300 Pitch 550 Pitch 800 DR3 31dB 40.3db 47.6dB DR3 is the Dynamic range between the fundamental and the 3rd harmonic (the most dominant harmonic by a wide margin) I did a quick look at 5th and 7th orders too, again the best performance here was found with LIN = 100 LIN = 100 is an output level of approximately 700mv for an S9 CW sig on my K3 The Harmonic distortion does not increase with higher line out levels, it actually improves. This does not appear to be a transformer saturation issue With lin = 100 users will see a ghost on the waterfall and may risk over-driving some consumer sound cards. lowering LIN may get rid of the visible ghost by reducing the 3rd Harmonic to below the waterfall threshold (& perhaps the sound card input noise floor ) but also reduces the overall usable dynamic range 73 Brendan EI6IZ -- Don‘t complain. Nobody will understand. Or care. And certainly don‘t try to fix the situation yourself. It‘s dangerous. Leave it to a highly untrained, unqualified, expendable professional. _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
