There are multiple settings which easily impact this. As Alex correctly states, one size does not fit all.
Take the RF gain and turn it down until the noise floor is not objectionable to you and then slow down the agc time constants. I either like SLOW in almost all rag chew cases or Customize settings. 73's Bob N4HY Tayloe Dan-P26412 wrote: > 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/ > > -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "Taking fun as simply fun and earnestness in earnest shows how thoroughly thou none of the two discernest." - Piet Hine _______________________________________________ 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/
