[time-nuts] xtal oscillator phase noise

[Richard (Rick) Karlquist]

In the HP 10816 Rb frequency standard, we used a modified
10811 oscillator circuit.  The oscillator and first buffer
amplifier transistor were the same, but the rest of the
buffer amplifier was replaced with a cascaded grounded
base buffer amplifier.  We were able to get numbers comparable
to those shown below.  The ultimate limit at large offsets
(as Burgoon's patent teaches) is determined by the crystal
current, which has to overcome the shot noise of the grounded
base buffer.  The 10811 uses 1 mA RMS crystal current.  You
can turn this up and get even better phase noise, but then
you might degrade the stability of the crystal.  The stock
10811 has an output circuit that degrades the phase noise.
There are various reasons for why this was done including
backward compatibility with the 10544.  Few, if any, HP
instruments would actually benefit from the extremely low
phase noise.  The 10816 was different, since it was meant
to be sold as a component, not used in an HP instrument,
and we could advertise the spec.  Unfortunately, the 10816
project was cancelled by new management after the pilot
run.

BTW, Rob Burgoon, one of the designers of the HP 10811,
is going to retire from Agilent this month.

Rick Karlquist N6RK

Tom Van Baak wrote:
>> For what it's worth, the Wenzel 5 and 10 MHz ULN oscillators are
>> generally considered to be about the lowest noise oscillators
>> commercially available.  They really shine in their noise floor.
>> There's actually (at least) one 5MHz oscillator with a better 1Hz offset
>> spec -- the Oscilloquartz 8607-08 BVA at -130 dBc/Hz, though its noise
>> floor at about -160 dBc/Hz is nothing like the Wenzel's.
>>
>> Here's some data on the Wenzel units from their web site:
>>
>> 5 MHz 10 MHz
>> 1 Hz -120 -105
>> 10 Hz -150 -135
>> 100 Hz -170 -160
>> 1 kHz -176 -173
>> 10 kHz -176 -175
> 
> John,
> 
> Good timing; yesterday, John Miles was over here to test some ULN.
> Here's a Wenzel ULN 5 MHz against a ULN 10 MHz.
> http://www.leapsecond.com/museum/wenzel-uln/uln5-uln10.gif
> (these are relative measurements; absolute would be ~ 3 dB better)
> 
> Also, for those interested, two 8607-08 BVA against each other:
> http://www.leapsecond.com/museum/osa8607/8607-8607.gif
> 
> /tvb
> 
> 
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