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.

Doesn't sound to bad really. A one second scan across the entire 100MHz is fine
really (depending on what your doing) - the PC is a perfect storage scope.

To convert a linear I/Q baseband sample to a log scale is no problem at all in
software.

The software cud easily deal with any variation in VCO/Mixer level differences
across the whole band.

Best to have the PC control the vco though, then as you say, you can zoom in on
a desired freq range etc.

Clive