Re: Comparing timing between sinusoids at different freqs

On Jul 9, 11:18 am, "Wally" <nos...@xxxxxxxxxxx> wrote:
I have a requirement to measure the relative timing between two sinusoids
for the purpose of determining the relative circuit delays between the
sources and me.  I have no control over the sources, but they are highly
stable fixed frequencies.  The measurement technique I use would be done at
the sources themselves, and simultaneously at my receiving point, with the
change in relative timing representing relative circuit delay.

If the sources are at the same frequency I can do simple relative phase
measurements at the sources and at my receiving point.  Unfortunately they
are at slightly different (0.01%)  frequencies, which makes their relative
phases time-dependent.

One possible solution I have in mind is to compute the average zero crossing
times of the two sinusoids over the same measurement interval, and compare
those averages.  I imagine that even though the zero crossing times are
changing on a relative basis during the measurement interval due to the
frequency differences, the averaged zero crossing times will still give a
unique answer for relative timing determination.

Another way might be to shift one of the frequencies in my test equipment so
the two frequencies are equal, then make a relative phase comparison.
However, is the effect of this frequency shift on signal phase predictable?

I'm out of my comfort zone here and will be grateful for any advice.

Wally,
From what I read, it appears that you can measure the phase diffrence
of the two signals at the source, and the phase difference of the two
signals at the receiver, but you can NOT measure the phase difference
at the receiver relative to the source. The ONLY measurement you have
is the phase difference of the two signals either at the source or the
receiver. Is this correct?


Maurice Givens

.

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