[time-nuts] Re: What about the frequency discrimination method? (offshoot from DIY PN analyzer)

[Azelio Boriani]

How can you measure something, any type of measure, not only PN,
without a reference? Voltmeters need voltage references, "timemeters"
(and frequency meters) need time references.

On Sun, Jul 10, 2022 at 1:47 AM ed breya via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> I've been following the thread about Erik's DIY PN analyzer, and
> wondering if it might be easy enough to use a frequency discrimination
> method. I'm opening this in a different thread to avoid muddying the
> water on the original (and long) one.
>
> What I'm picturing is putting the DUT's output into a quadrature power
> splitter that optionally has a voltage-tuned slight phase shift feature.
> The I and Q outputs would go into the DBM and produce the nearly-zero DC
> plus baseband signal for analysis as in the original story.
>
> If the quadrature is precise and stable enough, the DC out should be
> close to zero, and since the baseband is ultimately AC coupled to the
> analyzer, small offset should be OK, within reason.
>
> If this is not sufficient, then having a phase tuning feature could be
> used to form a PLL to hold the DC at zero. The big difference here is
> that instead of locking a separate reference source to the DUT, the
> relative phase at the mixer just has to be fine tuned to maintain the
> output DC. The same sorts of PLL requirements are encountered to get the
> results, but no external reference (and its noise and lock range etc
> issues) is needed.
>
> The downside is that a different quadrature splitter would probably be
> needed for each DUT frequency to be applied - I'm picturing ones for 5
> and 10 MHz initially. Those 90 degree broadband splitters that Mike
> mentioned seem very interesting too.
>
> There is still the necessity of calibration, either way.
>
> Ed
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