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

Mark J. Blair nf6x at nf6x.net
Fri Aug 20 17:23:35 UTC 2010

On Aug 20, 2010, at 7:40 AM, Adrian wrote:
> - you may build your own HP 3048A alike system, but be prepared to invest serious money and time, and much more time than you thought in the beginning... (if that is what you're after, you'll have the most fun you can).

I did a quick survey of surplus phase noise measurement system prices on eBay, and was shocked by how cheap they apparently aren't. I'll set up some searches to warn me when any of the instruments you mentioned appear, since it may be a while before the right one shows up at the right price.

> - Compare 3 similar DUT's  with a HP 3048A and calculate the individual PN using the three cornerd hat method.

That sounds like a method I'll want to learn about, since I'll necessarily be building up my testbench with surplus equipment of unknown condition, and the things I'd want to characterize initially would likely be the best oscillators I can get my hands on (except for the ones that no longer perform to spec, which I'd want to weed out). Once I have the bugs worked out of my test system, I could then use it to characterize other oscillators (probably far inferior to the Trimble/HP OCXOs) in practical applications.

> Btw. do not assume that the phase noise of a disciplined VCXO is the same as the VCXO alone.
> Also keep the power supply contribution into account that can be surprisingly high.

In the case of my TBolt OCXO, I'll be interested in characterizing it while it's in the TBolt, with its regular power supply, and under discipline, since that's the way I'd be using it as a frequency reference on my bench.

> And, the PN of most frequency standards is significantly lower than what you can measure with any spectrum analyzer with PN measurement software (except for the R&S FSUP of course).

Yup, the phase noise plots I've seen of the HP and TBolt OCXOs show close-in phase noise very far beyond the dynamic range of any spectrum analyzers I'm familiar with. I wandered through the labs at work in hope of finding something I could use to look at the phase noise of my new toys (I'm in the GPS industry, and have access to some nice spectrum and network analyzers), but it looks like I'm on my own.

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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