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

Rick Karlquist richard at karlquist.com
Fri Aug 20 18:17:00 UTC 2010

Mark J. Blair wrote:
>> 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.

Right, the delay line method is a non-starter.

>> 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.

On the 10811 production line, they would use Anzac AMC-123 amplifiers
to drive a +17 dBm mixer, and then amplify the IF output with a low noise
current amplifier like the Linear LT1028.  You can easily homebrew
this setup.  You will need to have a DC coupled connection to the IF
output to make a narrow PLL that drives the EFC of one of the oscillators.
You can use a PC based audio spectrum analyzer program to look at the
phase noise output.  You can break the PLL to get a beat note to calibrate
the system.  The AMC-123 can also be homebrewed by reading the
patent, which is listed on the data sheet.  No need at all to get
a 3048, etc.

Rick Karlquist N6RK

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