Re: Basics of Frequency Shifting

The problem is unusual in that I don't have physical access to either the
sources or the circuit inputs. They are remote. I am stuck with having two
independent sources at slightly different frequencies arriving via
independent circuits with different delays. What I do know is the relative
signal phases at the sources at a specific time.

So one way to determine differential circuit delay is to measure relative
phase of the arriving signals at the same time when the relative phases are
known at the sources. However this is subject to errors in measurement
time.

I'm trying to reduce or eliminate sensitivity to time of measurement by
shifting both received signals to a common frequency. The shifting process
may alter the signal phases, but it should do the same to both circuits
thereby not affecting the relative received phases that I want to measure.
Conceptually is there a flaw in this approach?



"Rune Allnor" <allnor@xxxxxxxxxxxx> wrote in message
news:85e39370-5113-48a7-b347-b3d048ee8ccb@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On 6 Nov, 06:20, "Mason" <plsnos...@xxxxxxxxxxxxx> wrote:
Sorry if I was not clear.

I have no control over the sources. The two sines are correlated in that I
know their relative phase at a specific time at the sources. They are at
slightly different frequencies and arriving through two circuits with
different delays.

This is a very elaborate way of saying that you have two
independent sources. The fact that you can compare them
at one time does not change the fact that they are independent.

I'm measuring the difference in time between selected
events in the two sines - ie, waveform maxima

Beginner's mistake. It's way easier to use zero crossings
if you want accurate timings.

- to determine the difference
in the circuit delays, and I'm making that measurement at about the same
time when I know their relative phase at the sources.

If you want to measure or characterize each of the cirquits,
then investigate each cirquit on its own.

The problem is, errors in the time of measurement cause inaccurate
measurement results because the waveforms are moving relative to each
other
vs. time as a result of their different frequencies.

That's a problem you can't solve. The reason you have that
problem is that you have chosen a very bad strategy to solve
a seemingly standard problem.

So I believe a solution is

Don't believe. Investigate.

to shift the frequency of each signal to a
nominal frequency. This would eliminate the requirement for precise
measurement time because the sines will no longer have time-dependent
phase
difference.

Of course. "Eliminate the requirement for precise measurements."
Contemplate that sentence. Why not re-iterate the argument of
yours and get rid of the "frequency normalization" and eliminate
the need for measurements alltogether?

The frequency shifting process will affect the signal phases
but I believe it will affect both signals the same and therefore not alter
the phase difference due to different circuit delays that I am trying to
measure.

If you want to investigate cirquit delays, then investigate
cirquit delays. Quit messing about with BS.

Am I going in the right direction?

No.

Rune


.

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