>From G3PLX: Gerald: Thanks for your response with comments on 1/f noise and image balance.
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. Some circuits 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. There is certainly no sign of it at the input of Gerald's elegant post-QSD amplifier in the SDR1000, which has clearly been designed for the ultimate in low-noise performance, since that's where the signal level is at it's lowest. To me this says we shouldn't be frightened of 1/f noise. 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. To do this I 'worked round' the oscillator re-radiation noise by including a unity-gain frequency-conversion (in hardware) before the SDR1000, so it's not a final solution but a demonstration of a possibility. I hoped I could send this to the reflector so that others can listen to it, but this may not be possible. I can email it to anyone who would like to hear it. 73 Peter _______________________________________________ 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
