[Elecraft] SDR-IQ

[Alan Bloom]

The answer is "it depends." :=)

The tentative spec for the noise figure of the P3 itself is 10 dB,
although it typically is a couple dB better than that.  If you do the
math, the noise figure of the K3/P3 system is within a dB or so of the
NF of the K3 alone.

But how does that translate to what you can see on the P3 screen?  At
maximum span (currently 200 kHz), the effective resolution bandwidth is
a bit less than 500 Hz, so you should be able to see anything with a
positive signal-to-noise ratio in a 500 Hz bandwidth.  Actually you can
do quite a bit better than that using the waterfall display because the
human eye has an incredible ability to discern patterns.  A weak signal
that is hidden on the spectrum display is clearly visible on the
waterfall.

But the narrower the span the weaker the signal you can see.  Unlike
most band-scopes and SDR-based panadapters, the effective resolution
bandwidth of the P3 automatically improves as you reduce the span.  At
the minimum 2 kHz, the effective resolution bandwidth is less than 5 Hz.
You can easily see signals that are completely inaudible in the
headphones.

Alan N1AL


On Tue, 2010-06-08 at 20:29 +0100, David Cutter wrote:
> I wonder what the "sensitivity" of the P3 is in this regard; I can't see it 
> in the spec on quick inspection.
> 
> David
> G3UNA
> 
> 
> 
> 
> 
> >
> > George
> >
> > I have a K3 s/n 3569 (factory built) which has RF Board Rev 3. I have also
> > checked inside the radio to see that the IF output modification has been
> > performed.
> >
> > My experience with the SDR-IQ is also disappointing. There are signals 
> > that
> > I can hear on the K3 (up to S4 or 5) that I simply cannot see on the
> > Spectravue panadapter. This is despite me setting the SDR-IQ to maximum 
> > gain
> > - but maybe I'm missing something too.
> >
> > I'd also be interested to hear from anyone who already has the Rev 3 RF
> > board and has SDR-IQ on the IF output working satisfactorily (i.e. can see
> > weak signals!).
> >
> > John G4IRN.