Then again, direct sampling SDR don't have an LO to leak, but do have a stable clock. There are some power supplies and digital systems with spread spectrum clocks. No reason one could not use a spread spectrum ADC clock, heavily over sampled of course, then average the samples where needed. There are some ADC they randomize the data bus for EMC.<p>Do they still have vans in the UK that driving around looking for un-taxed TV?
It is a very interesting topic because almost all electronics devices have similar emissions , see <a href="http://www.cvel.clemson.edu/pdf/ED_Detection_2008.pdf" rel="nofollow">http://www.cvel.clemson.edu/pdf/ED_Detection_2008.pdf</a><p>Someday thieves will use these techniques to locate who in a dark alley has the latest iPhone.
This cat-and-mouse game has been going on for a long time, even outside of spycraft.<p>E.g. radar detectors are illegal in several states, so of course there have been devices sold to law enforcement to allow them to detect these illegal radar detectors. <a href="https://en.wikipedia.org/wiki/Radar_detector_detector" rel="nofollow">https://en.wikipedia.org/wiki/Radar_detector_detector</a><p>That's all probably moot now. I think law enforcement has moved mostly to using lasers, which are much more difficult to detect.