On 5/24/06, Peter Martinez <[EMAIL PROTECTED]> wrote: > > I am really not convinced that 1/f noise is 'physics' in the same sense as, > for example, thermal noise is physics which we can't fight.
Who says you can't fight thermal noise? Just use liquid nitrogen or helium to cool your circuits! On a more serious note: Of course different circuits will exhibit different noise characteristics, but that doesn't make 1/f noise any more less "physics" than thermal noise. All this discussion may be beside the point, however, because I don't think 1/f is a very significant problem in sounds cards or SDR-1000. > exhibit what we term 1/f noise and others don't seem to do so, so I > speculate that if we are careful we can design it out. I can see it in my > cheapo MP3+, Sami sees it, but Alberto's plot of the Delta 44 spectrum and > my results on the Firebox don't show any significant low-frequency noise. Actually, I don't see any 1/f noise. Or maybe very little, but most of the near-DC noise is 50 Hz and its multiples just like you suspected in a previous post. I'm fully aware that my grounding setup is nowhere near perfect, but I know many SDR-1000 users have similar or even worse problems. > I have done a WAV file of an SSB signal received 15dB above noise, received > on my SDR1000 into the Firebox using Zero-IF software, and there's no sign > of a noise peak in the centre. I have done this kind of demonstration myself. It works, but I obviously can see and hear some noise. But please send your file directly to my e-mail address. There's one more reason why using a non-zero IF can be useful. If you're using zero IF, you have to use the exact DDS tuning word that takes you to the frequency you're listening to. But some tuning words will generate a lot of spurs, and there's no way you can avoid them. With non-zero IF you can have 40 kHz (or 90 kHz) of DDS frequencies to choose from. Of course, the current PowerSDR software doesn't yet offer this possibility. 73, Sami OH2BFO _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
