[time-nuts] Home made GPS disciplined atomic clock

[Esa Heikkinen]

Hello again...

> Right, it all depends on what stability you're after. The OCXO
> will have much better short-term stability than the LPRO -- the
> LPRO is close to ten times worse. So do not replace the TBolt
> OCXO with a LPRO if short-term stability is your goal. See:

I'm wondering what could be the cause of this. According to operating 
manual LPRO's output should be crystal oscillator (VCXO) generated 
signal, which is synchronized to rubidium. So why it is so much worse 
than any other crystal oscillator (or other Rd oscillators). Are there 
any schematics for LPRO available anywhere?

I cannot see the any phase noise difference between Trimble's OCXO and 
LPRO with spectrum analyser. Measured with different spans from 500 kHz 
to 200 Hz, using resolution bandwiths 300 Hz to 6 Hz. So the noise which 
is causing bad short term drift must be very close to fundamental.

It seems that only way to see this noise is to use phase detector 
circuit but my problem with that is that I haven't got any good 
reference for it and this kind of equipments are quite hard to find here 
in Finland. It would be nice to see what kind of noise there are, to 
design the filter bandwith for external OCXO lock circuit.

Other idea to bring that noise visible could be multiplying it with some 
kind of comb generator circuit (might be hard to build one). Then it 
would be possible to measure it's harmonics. Not sure if there's enough 
level present anymore at GHz frequencies...

What kind of test setup did you use when getting this result:
 > LPRO plots:
 > http://www.leapsecond.com/museum/lpro/

-- 
73s!
Esa
OH4KJU