[time-nuts] How do time-nuts measure phase noise?

WarrenS warrensjmail-one at yahoo.com
Mon Aug 17 13:49:46 UTC 2009


Antonio I8IOV

see wenzel link for nice clear write-up of one way to do it.
http://www.wenzel.com/documents/measuringphasenoise.htm

Because most Freq test show differences, The one thing you need is a good reference to compare to.
To get numbers without the detailed freq information of the phase noise when you don't have the spectrum analyzer,
you can use just an AC voltmeter and band pass filter to measure the noise at the Phase detector Amp output.
But you have to be careful and know what you're doing, 
And if you already know what you are doing, you probable have all the extra time nut stuff.

ws
*********************
----- Original Message ----- 
From: <iovane at inwind.it>
To: "time-nuts" <time-nuts at febo.com>
Sent: Monday, August 17, 2009 4:51 AM
Subject: Re: [time-nuts] How do time-nuts measure phase noise?


On Mon, 17 Aug 2009 23:18:58 +1200 Bruce Griffiths wrote:

> >   
> >> iovane at inwind.it wrote:
> >>     
> >>> Please, how do time-nuts measure phase noise? What may be a minimal setup whit recording capability?
> >>> Thanks,
> >>> Antonio I8IOV
> >>>

> >>>       
> >> snip

> 1) Use 3 sources, S1, S2 and X.
> 
> 2) Phase lock S1 in quadrature to X using a diode double balanced mixer
> using a low bandwidth PLL.
> 
> 3) Phase lock S2 in quadrature to X using a diode double balanced mixer
> using a low bandwidth PLL.
> 
> Then for frequencies outside the PLL bandwidth the crosspower spectrum
> of the 2 mixer outputs should be predominantly due to the phase noise X.
> 
> In practice its best if the phase noise of the 2 standards S1, S2 isn't
> significantly worse than that of X.
> 
> It is also desirable that both S1 and X and S2 and X be locked at their
> respective mixers quadrature point (not necessarily the same as that for
> zero dc output)
> 
> Bruce

Bruce,

is this what actually time-nuts do? This is unpractical for me, as I have not much 
time for a circuit building project. Moreover, I would be satisfied even with the 
analysis at a single frequency, not necessarily the whole phase noise spectrum, 
and with relative but repeatable measurements.
So, does it make any sense using a selective voltmeter, such as an HP 3586A or 
similar? 

Antonio I8IOV








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