Peter, To Sami's comment I want add my purist's 0.02 Euro worth:
1/f noise is real, but cannot be easily seen in the present implementation of the SDR-1000 hardware. As a good designer Gerald has hidden it by: 1) putting the preamplifier gain so high that the noise coming from the front end masks all other noise and 2) selecting the IF frequency (11.025 kHz) well away from the worst 1/f noise area. Already these design decision were enough to make a pretty good receiver for the average ham radio operator on HF bands. Adding the front end gain increases the dynamic range at the weak signal end but limits it with the strong signals as the QSD can stand only about 1.5 Vrms. Ignoring everything else, the 20 kHz wide noise of the output stage alone without signal is about 8.5 uVrms. That calculates roughly to 105 dB blocking range before the sound card. Not bad! But because I know that better is possible with normal price and off-the-shelf components, I wait for the results of the JANUS project. Possibly some minor hardware modifications and adjustments will be necessary in the SDR-1000 to match the promised 120 dB dynamic range of JANUS. 73, Ahti OH2RZ On 24/05/06, Sami Aintila <[EMAIL PROTECTED]> wrote: > 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 > _______________________________________________ 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
