On Tue, Feb 2, 2010 at 1:17 AM, Simon HB9DRV <si...@hb9drv.ch> wrote: > Random thoughts: > > You shouldn't have any spurs, that's it. Even though the spur is ~60dB down > on the main signal it'll be easy to decode and just shouldn't be there. > > As Tim says it could well be a soundcard harmonic *but* you're using VAC, in > which case it would have to be generated inside the VAC driver and this is > indeed possible. > > If possible look at the signal fed into the VAC, maybe I'll have to write a > display to show this. > > Is the VAC running at 8kHz both ends or is the end connected to PowerSDR > running at a different rate? If so this could account for the spur. > > Simon Brown, HB9DRV > http://sdr-radio.com
This problem appears with both fldigi and dm780. It also seems to change over time. (Changes to libraries?) It appears to me to be aliasing products which make me suspect sample-rate conversion used in either fldigi, dm780, VAC, PowerSDR, or some combination thereof. I have tried changing the sample rate in/out of PowerSDR to match the sample rate used by the different CODECs in fldigi so that there is only one sample-rate conversion taking place. This definitely turned out to be a lose, leading me to suspect that the sample-rate conversion code in PowerSDR is suboptimal. Dave did make some changes to fldigi in generating the waveforms for Olivia which helped tremendously but I still see things change periodically. -- 73 de Brian, WB6RQN/J79BPL _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
