[time-nuts] 'Discussion of precise time and frequency measurement'

Francis Grosz fgrosz at otiengineering.com
Wed Jun 16 14:52:07 UTC 2010


     If you have an analog 'scope with delayed sweep, set it up with the main time base
showing the 90 MHz signal in a convenient way (say 1 cycle/div) and then 
use the delay to look at the signal some time later (after the initial trigger) with
the modulation on and off.  Any phase or frequency modulation should be pretty
 obvious then.  (Note:  Use delayed sweep, NOT delayed trigger; i.e., "B starts
after delay", not "B triggerable after delay".)

                    Francis Grosz

Original Message

It's been a long week and it's only Tuesday.

How can I prove that the A3 assembly is, in fact, phase modulating?  In
other words, how can I prove that the 90 MHz signal from the A3 assembly to
J1 on the A4 assembly is phase modulated by the 137 Hz signal?

I have looked at the output of the A3 assembly at the cable to J1 on the A4
assembly (A4P1) with an oscilloscope and a spectrum analyzer with Mod On and
Mod Off and can see no difference.  Likewise, on a functioning unit, I can
not see any difference there either.  Are there proper ways to set up the
scope or SA to focus on this issue?

Short of fabricating a 'phase detector', how can I prove that the A3 unit is
functioning in my 'problem child' unit.  If I have to fabricate a 'phase
detector', how easy (or difficult) is that?



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