[time-nuts] HP 53131A question

[Tom Van Baak]

> Hi all,
> 
> I'm planning to use a HP 53131A for phase measurements. 
> In a limit case, just to understand, suppose that I'm 
> reading, say, 100 degrees, and the next reading gives again 
> 100 degrees, but meanwhile the signal under test jumped 360 
> degrees. Is there any way to detect such a case? 
> 
> Thanks in advance,
> Antonio I8IOV

That's a good question for the purpose of understanding.

In general, no. So you have to pick your sampling rate to be
somewhat faster than the expected maximum cycle drift rate
(Nyquist has something to say related to this).

As a further example, the same thing would happen to the earth,
if while you were sleeping it quickly sped up 3x normal speed
and slowed back down to normal. You'd wake up, see a sunrise,
and think it was Saturday morning. Instead it would actually be
Sunday morning. You were sleeping; how would you know?

Now if there were a special application where detecting phase
jumps like this was critical you could drive two free-running
counters, one from the input signal, one from a reference clock,
and compare them as often or as infrequent as you wish. A
"continuous count" or "zero dead time" counter works this way.
But a 53131A is isn't of this design.

Magnus' suggestion about dividers is perfect. It is what many of
us do with our clocks -- instead of measuring phase angle between
two 5 MHz RF signals, we divide 5 MHz down to 1 Hz and leisurely
compare the time interval of 1PPS signals, as often as once a
second or even as infrequently as once an hour or day.

/tvb