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

[Bob Camp]

Hi

I've always calibrated my phase noise setups to the phase slope of the mixer
I'm using. It does involve switching gains, but it's a direct system
calibration. Beat note is 360 degrees, so this chunk is x degrees and you
got y mv over that chunk. Check the slope on the other side of the beat note
to make sure it's the same. Do some math and you have a radian to volt
transfer function. 

If you are sorting junk box OCXO's it's a pretty good way to do it. The only
added steps are an independent measurement of the switched gain / gain
flatness and a short circuit input check to estimate the noise floor. Both
are an initial setup / one time only sort of thing with most amps. 

Bob 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bruce Griffiths
Sent: Tuesday, August 24, 2010 3:25 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Phase noise measurement (was - no subject)

Bob Camp wrote:
> Hi
>
< CHOP >
....
Being able to calibrate the preamp + sound card frequency response using 
the thermal noise of a resistor is convenient.
This is more difficult to achieve with a bipolar input stage as the 
amplifier input current noise is significant.

Bruce


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