[time-nuts] Re: Can one use a two channel TC with an internal reference to measure two independent oscillators to establish the quality of the internal reference?

[Bob kb8tq]

Hi

Usually the best / quick / easy way to evaluate something like
a two channel counter is do it with a pair of signals that are independent
from each other, but very close to the same frequency. Rb’s are often
used, but the technique is not specific to them. 

You feed a PPS ( or whatever ) from each source into your channels. 
The reference for the counter is “something else”. As the two PPS
edges move along relative to each other, you sweep out the range
of the device. What you typically find is that the gizmo isn’t quite as
linear as you had hoped. You might even find dead spots ….

Bob

> On Apr 2, 2022, at 3:10 PM, Erik Kaashoek <erik at kaashoek.com> wrote:
> 
> During evaluation of a two channel TC that can measure simultaneously the
> phase of two external oscillators the need came to understand the quality
> of the internal reference while eliminating (some) uncertainty of the
> performance of the two external oscillators.
> The 3 cornered hat method comes to mind as a way to get insight but I am
> sure I do not understand this all good enough.
> Some practical info on the setup:
> Two channel TC with 4 ns clock resolution and capable to measure phase
> against it's internal clock using interpolation over maximum 50000 phase
> measurements per second.
> The external clocks being measured are a Rb with unknown performance and an
> OCXO with unknown performance.
> Any advice on how to create a better understanding of the performance of
> the internal reference using the above setup?
> Erik.
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