Hi Eric,
Well, I'm sure with antenna on the preamp output is noise floor +
amplified (atmospheric noise + signal.)
With the dummy load while on 20M CW, I get the following RX Meter and
Panadapter noise readings. (Panadapter readings are eyeball of course.)
Also I'm taking the RX readings on noise with the 25 Hz CW filter.
RX Meter Pan Display
Preamp Off -117 dBm. -115 dBm
Preamp Low -117 dBm -117 dBm
Preamp Med -125 dBm -123 dBm
Preamp High - 125 dBm -125 dBm
Readings would be constant except for that step between Low and Medium...
vy 73
Rob
AB7CF
On Fri, 25 Jan 2008 10:41:56 -0600 "Eric Wachsmann" <[EMAIL PROTECTED]>
writes:
> Could this be due to atmospheric noise? Have you tried this on a
> dummy
> load?
>
>
> Eric Wachsmann
> FlexRadio Systems
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]
> > radio.biz] On Behalf Of Robert Dennison
> > Sent: Friday, January 25, 2008 10:29 AM
> > To: [EMAIL PROTECTED]
> > Cc: [EMAIL PROTECTED]; flexradio@flex-radio.biz
> > Subject: Re: [Flexradio] gain on the sdr1000
> >
> > Hi Jim,
> >
> > Well, yes t'would be nice to have the panadapter display the input
> to the
> > preamp, but mine displays the output from the preamp.
> >
> > Clearly the signal is amplified by the same gain as the noise...
> In my
> > case as I increase the preamp gain a notch the noise level is
> amplified
> > by say 5db and the signal magnitude floating on top of the noise
> is
> > amplified by the same amount. RX Meter with Sig Avg shows the
> same
> > result. Also, near as I can tell by ear and eye the preamp is not
> adding
> > additional noise.
> >
> > Near as I can tell from the panadapter and RX Meter, my preamp is
> working
> > like a near perfect linear amp.
> >
> > Yes, powerSDR, having some idea what the preamp gain, is can back
> it out
> > of the display, but I've run every version of PowerSDR from 1.8 to
> 1.10.3
> > and they work exactly the same as I've described and measured. I'm
> now
> > running SVN: 1917 and it's behaving as I described.
> >
> > Have I found a weird display mode? I'm too good at that for my
> own
> > good...
> >
> > vy 73
> > Rob
> > AB7CF
> >
> >
> > On Fri, 25 Jan 2008 06:40:48 -0800 Jim Lux
> <[EMAIL PROTECTED]>
> > writes:
> > > 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)
> > >
> > >
> > >
> > >
> >
> > _______________________________________________
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> > FlexRadio@flex-radio.biz
> >
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> http://www.flex-
> > radio.com/
>
>
>
>
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