[time-nuts] Phase noise measurement (was - no subject)

Mark J. Blair nf6x at nf6x.net
Fri Aug 20 17:11:50 UTC 2010


On Aug 20, 2010, at 4:56 AM, Grant Hodgson wrote:
> You've come to the right place - well, that is if you want to devote a significant amount of your life in the pursuit of ever-more accurate time and frequency measurements....

:)

> If you've only got one source then you need to use the frequency discriminator method (aka delay line method) of phase noise measurement.  Basically you take the output of the source, split it in two, delay one of the signals, re-combine the two and then measure the resultant signal on a base-band spectrum analyser.
[...]
> The limitation of the frequency discriminator method is that the noise floor of the measurement system is often worse than the DUT, especially if your DUT is very good, and it's even worse if you're trying to measure close-in noise.  The Sherer article gives a good graph illustrating this. If you're trying to measure the phase noise of the oscillator inside a Tbolt then I don't think that a frequency discriminator will be sensitive enough, although I might be wrong.


I got the impression that for "good" OCXOs like the HP 10811 or (supposedly) the OCXO in my TBolt, the delay line method wouldn't provide enough sensitivity for measuring close-in phase noise.

> Despite what you said, you might want to consider buying an HP 10811 oscillator or similar which you could use in a phase detector measurement system which is likely to give superior results.

I might need 2 or 3 of them so I can weed out the under-performers! :) I had originally considered getting one of the surplus HP/Agilent GPSDOs with HP 10811 OCXOs, but I settled on the TBolt since it appeared to be almost as good (in terms of phase noise), a bit cheaper, and a bit easier to power than one of the HPs that need 48VDC. Well, I bought another power supply for the TBolt, anyway, but at least it would be easier to build a power supply that operates from +12VDC, a voltage that's always available in a ham shack.






-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.







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