I need to buy a DSO for probing some RF paths at around 460 MHz. The signals are QPSK at around 100 kbps. I'm not real familiar with DSO sampling requiements. The scope manufacturer guidelines seem to suggest a BW at least 4x the highest frequency to be measured, so than means around 2 GHz. That's a pretty expensive DSO.

Can I mix the sampled RF down first either to baseband or some IF and expect to get a good representation of the original signal? Of course that would mean making sure the conversion was done properly, but are there any good reasons to go ahead and sheel out the dinaros for an expensive scope vs. downsampling and using a less expensive scope? Thanks.

No reason to by 2GHz Oscope. You can downconvert and sample with a much lower cost digitizer. National makes some nice digitizers that give you resonable Spectral Analysis results. Just make sure you downconvert to a frequency range that gives you the full modulated bandwidth.

_________________
Sunshine Design Engineering Services