[time-nuts] Basic question regarding comparing two frequencies

[J. Forster]

The splitter makes two identical signals from Ref 1

The quadrature hybrid makes two signals out of Ref 2, but with a 90 degree
phase shift between the signals.

It's essentially a QPSK Demodulator, but set up to run in the linear
region, rather than clipping. It's also sometimes called an I-Q detector.

There is some closely related info here:

http://www.minicircuits.com/pages/pdfs/mod11-2.pdf

-John

===============




> My attempt to understand your diagram, not sure about how the quadrature
hybrid
> is connected.
>
> Stanley
>
>
>
> ----- Original Message ----
> From: J. Forster <jfor at quik.com>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Sent: Sun, July 25, 2010 10:29:23 AM
> Subject: Re: [time-nuts] Basic question regarding comparing two
> frequencies
>
> There is a cute way to use a scope.
>
> It requires a power splittere, a quadrature hybrid, and two mixers (all
appropriate for the frequencies you are comparing), and an X-Y scope.
Mini-Circuits sells appropriate parts. The stuff is hooked up like this:
>
>
>               X Axis
>       S      |      H
>       P ---- MIX ---- Y
> REF 1--L              B -- REF2
>       I ---- MIX ---- R
>       T      |      I
>               Y Axis  D
>
> The 'scope display will be roughly a circle if the frequencies are a bit
different and the spot will go around CW or CCW depending on which Ref
is
> higher.
>
> -John
> <snip>