[time-nuts] Stepping up the output of an OCXO

[John Ackermann N8UR]

Dr Bruce Griffiths said the following on 02/04/2007 02:32 AM:

> My calculations using the component values in the circuit indicate that 
> the TADD-1 noise figure should be about 19dB and its corresponding phase 
> noise floor should be lower than -160dBc/Hz. when the input signal is 
> +7dBm or greater. So unless you had an unusually noisy set of opamps 
> and/or resistors the measurement setup phase noise floor probably 
> exceeds that of the TADD-1 by around 20dB.

Thanks for running that calculation, Bruce!  I am somewhat suspect of
our test setup as the fellow who owned the 3048 had never done this type
of measurement before.  I also don't recall just what the input level
was for our test.

In the next month or so, I'm hoping to rerun the measurements with an
easier-to-use, if not actually better, phase noise system and will
report those results.

> With a 10V supply instead of 9V and a +13dBm input the phase noise floor 
> should be about -168dBc/Hz which is respectable but a few (~10) dB shy 
> of the state of the art.
> 
> The only way to achieve the state of the art performance with opamps 
> using a 9 or 10V supply is to use lower noise (2nV/rtHz appears 
> feasible) opamps pairs driven in push pull by an input step up (1:2 
> turns ratio) transformer with an output stepdown transformer driven in 
> pushpull by the 2 opamp outputs. The noisy 1K input protection resistor 
> would also have to be reduced in value as would the opamp feedback 
> network resistors.
> 
> NIST's 1995 distribution amplifier claims a phase tempco of 0.3ps/K and 
> 120dB isolation between channels.
> http://www.physics.nist.gov/News/Update/950626.html
> 
> Bruce
> 
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