It was nothing special. Just a simple SDR receiver; front end, detector, and audio preamplifier. I just threw something together to work with a 40m transmitter I was working on. It just struck me how noisy it sounded running with AGC turned on compared to my other NC2030 type phased narrow band rigs. The AGC just brings the band noise up when no other signal is present. - Dan, N7VE
________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Sunday, January 21, 2007 3:35 PM To: Tayloe Dan-P26412; flexradio@flex-radio.biz Subject: RE: [Flexradio] Noise floor driven, threshold based AGC? Hi Dan, I wonder what homebrew this was, and what soundcard was used. My experience is that the SDR1000 can be very quite when you set the RF gain. I like to know what is happening in the homebrew situation (more than curious) 73 peter pa0pvn groeten Peter petervn(a)hetnet.nl <mailto:[EMAIL PROTECTED]> ; pa0pvn(a)hetnet.nl <mailto:[EMAIL PROTECTED]> ; pa0pvn(a)gmail.com ; pa0pvn(a)amsat.org . ________________________________ Van: [EMAIL PROTECTED] namens Tayloe Dan-P26412 Verzonden: zo 21-1-2007 21:54 Aan: flexradio@flex-radio.biz Onderwerp: [Flexradio] Noise floor driven, threshold based AGC? I was listening to a homebrew SDR receiver last night and it stuck me how noisy it was compared to my analog, narrow band NC2030. As I thought about this for a bit, I think the reason that the NC2030 is so quiet (besides close attention of audio chain details), is that it has no AGC. Thus, I can turn the volume down to where the background noise is not that high, and tune around the band for signals, and signals tend to jump out of the (relative) silence and thus tend to stand out against the background a lot better. Given the fact that we have complete flexibility over the AGC in software, I was wondering if we could do something similar, but better. Suppose the receiver does an average noise level calculation over the sampled bandwidth (min function?) and then set an AGC threshold above that point (10 db?). If the signal falls into the range of the noise level up to the new AGC threshold, the signal comes through linearly amplified. If the signal is higher than the threshold, AGC is applied to keep it from blasting and or distorting away. This might give the best of both worlds where the noise floor is not needlessly amplified, producing a "quiet" receiver, but where AGC kicks in when needed to keep large signals under control. This could produce audio that is much more "listenable" than the current AGC amplified situation and more controllable than the "AGC OFF" alternative. - Dan, N7VE _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20070121/0804bf8a/attachment.html _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/
