Actually, undersampling does use the alias effect to bring down the RF carrier. That is, the direct sampling radio concept cannot avoid the aliasing: it is exploited to avoid, for example, to sample a 2GHz carrier modulated with a 20MHz signal with a 4Gsample/second ADC (by the way, does it exist?). A simple 20Msample/second ADC would be enough. Yes, to analyze an analog signal in real time I doubt you can use this method, if the signal is periodic maybe... you can advance the sampling trigger a bit, cycle by cycle, and reconstruct the whole signal after this little amount has covered a full cycle.
On Thu, Feb 23, 2012 at 10:56 PM, Jim Lux <jim...@earthlink.net> wrote: > On 2/23/12 1:25 PM, Robert LaJeunesse wrote: > >> FWIW Rigol pushes their 40MHz Analog Devices part to 100 MHz without any >> problem >> (seen in eevblog teardown). Yes it's sort of cheating, but if the part >> works >> fine because all of the suppliers parts now yeild that fast due to an >> improved >> process well, it saves a few dollars / quid / drachma... >> >> And the 40MSPS is over full temp range, likely this is not a problem for >> the DSO >> 203 which has NO temp rating. >> >> Yes the "72MHz analog" channel rating makes no sense for something >> sampling at >> 72MSPS, Nyquist says you get at most 36 MHz bandwith. >> > > That doesn't mean you couldn't use a sampler running at, say, 50 MSPS to > look at a 110 MHz signal (something we actually do in a radio). > > There are lots of ADCs out there that have RF bandwidths of much more than > the sample rate, intended for use in direct sampling receivers. What > performance really depends on is how good the sample/hold or track/hold is > and what the sample jitter is. (and of course, whether there's a stage in > front to keep unexpected signals from aliasing in) > > There are several ADCs out there that have GHz bandwidths and max sample > rates in the 100MSPS range. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.