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   tom jennings (tomjennings@tldr.nettime.org)'s status on Friday, 10-Jan-2025 08:45:16 JST tom jennings

   in reply to

   • F4GRX Sébastien

   @f4grx

   CLEVER BASTARDS!

   You may know all this already, my apologies if so, but the techniques used to create radar energy, megawatt pulses, nanoseconds long, using vacuum tubes that couldn't do 1mhz are flatly amazing. And right into the front ends of receivers.

   Here, it's that view of electronics as physics, lost to all but RF and chip folk today (and at ummm crazy quantum levels).

   • pistolero likes this.
   • Embed this notice
     F4GRX Sébastien (f4grx@chaos.social)'s status on Friday, 10-Jan-2025 08:45:18 JST F4GRX Sébastien

     in reply to

     @tomjennings yep thats it. frequencies of A and B must be quite close, a PFD comparator like what is used in PLLs is better for coarser comparisons. then the delay between the two downconverted signals is measured.

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     tom jennings (tomjennings@tldr.nettime.org)'s status on Friday, 10-Jan-2025 08:45:19 JST tom jennings

     in reply to

     • F4GRX Sébastien

     @f4grx

     Ok so different 10mhz sigs A and B, with LF comparator C, you mix AC and BC, lopass filter those each, compare that?

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     F4GRX Sébastien (f4grx@chaos.social)'s status on Friday, 10-Jan-2025 08:45:20 JST F4GRX Sébastien

     Wow. TIL about Dual Mixer Time Difference phase comparison. The idea blew my mind.

     To measure phase between 10 MHz signals, you mix them with a slightly lower frequency. This produces a beat note, which can be low pass filtered. The two downconverted signals will have the same PHASE difference as the input signals.

     However, this phase difference on the beat frequency is a much longer DELAY with is very easy to measure. You can get sub-picosecond measurements of the 10 MHz phase difference.

     !!