Quoting Robert Dennison <[EMAIL PROTECTED]>, on Thu 24 Jan 2008 09:08:37 PM PST:
> Hi Ken, > > Now I'm confused. Must have something calibrated wrong or a bad 1K. > > My SDR1K is sitting on 7.010. Nothing but noise. Keeping AGC-T > constant: with Preamp Off the noise level reads -105dBm peak. Now if I > put the Preamp on Low the noise level jumps to -94dBm and when I put the > Preamp on Med the noise level jumps to -88dBm. Finally putting the > preamp on High the noise level jumps to -80dBm. > > To me that's what I would expect from a preamp. In fact first time I saw > it, I said to myself "now that's the way a preamp should work!" Not really... As you say, you're thinking in terms of the display reading what comes out of the analog section. But, really, you want the display to be reading what's at the antenna terminals (just like a lab spectrum analyzer). So, you adjust the scale according to how much gain there is. That way, an input signal of a fixed amplitude (e.g. at -100dBm) is always displayed at the same amplitude. The behavior you describe (measured noise floor getting bigger as amplifier gain is increased) is sort of upside down (Unless the amplifier is really noisy?) Is there something else going on? With a fixed level input signal, does the SNR stay the same? (i.e. the preamp isn't contributing significant noise) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
