wrote in message
news

I still think you stand a fair chance of problems, when essentially
you're
doing your signal strength measurement in baseband and sweeping at rates
in
the same frequency range. The aquisition time for the signal strength
measurement needs to be much shorter than the sweep, or the signal
strength
will change while you're attmpting to measure it.

Yes Sweep rate can be a problem, but it's all down the baseband bandwidth
and
what kind of update rate you want/need.

If you want to sweep across a 100MHz within say a second, assuming your
using
44100 sampling rate, that's 44100 samples you'll get across the 100MHz
sweep in
that one second - 2.26Khz wide freq segments (non-overlapping), but you'd
need a
baseband bandwidth of 1KHz to overcome the anti-alias problem.

The problem I'm having seeing how it can work is this. If you take 44100
measurements per second, that's one measurement every 27uS. But you've low
pass filtered your baseband at 1KHz. It would take at least one of those
cycles to measure the envelope amplitude with any degree of accuracy but
you're allowing just 2.7% of a single 1KHz sample, how does that work? Or am
I looking at it too simplistically?

I certainly agree that the PC can make a nice storage and display device,
specially if 'scopes aren't so easily available. Seems to me a question of
how much of the signal chain is implemented in analogue and how much in
digital. I Just think it saves an awful lot of hassle to add that little
extra analogue stage before you go digital, i.e. 2nd IF and detector. Log
could be done on the digital side no problem if desired provided enough ADC
resolution was available. VCO/Mixer level differences could still be
compensated in software, and the PC control the VCO.

Hans G0UPL
http://www.hanssummers.com