[time-nuts] Reference input on HP counters

Bob kb8tq kb8tq at n1k.org
Sun Jan 7 10:42:19 EST 2018


Hi



> On Jan 7, 2018, at 10:21 AM, Jerry Hancock <jerry at hanler.com> wrote:
> 
> I’m being a little lazy as I can check the schematics, but in the general case, do HP counters, frequency generators, etc, switch to the external reference when one is available or discipline the internal oscillator?

No, not if you are talking about the internal OCXO or TCXO.

>  Are there brands of test equipment that generally discipline vs switch?

Not that I’ve seen. 

The typical approach is to run a VHF oscillator and lock it to either the internal oscillator or to the 
external reference input. 

> 
> Third question, again generally, when you discipline an oscillator, what impact does this have on the oscillator's phase noise?  I assume this third question depends on the discipline loop (if I’m using the correct term).

Yes.

It also depends on how noisy the reference to the disciplining loop is. The most common case is 
that the reference is noisy at short tau. There is a tradeoff made in terms of how much noise is 
introduced vs how well things are disciplined. 

Bob

> 
> Thanks
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