[time-nuts] Lucent GPSDO comments

[Bob Camp]

Hi

The chain in the Z3810 / 3811 / 3812 Lucent boxes is *much* different than the setup in the earlier parts. The phase noise and ADEV on the Z3810’s is better than what you got on the earlier versions. That makes keeping the noise down in whatever mod you do more important. The existing 10 MHz output on the Z3810 setup is a real good example of how a seemingly simple thing can add a lot of phase noise and even mess up ADEV. 

I don’t think the 15 MHz is used for much of anything in the Z3810. That could be wrong, but I can’t see where it is needed based on poking around a little. The 15 MHz buffer appears to be quiet and puts out a lot of power. Using it for 10 MHz would give you a *lot* of 10 MHz signal to play with. IF the mods are simple it’s an attractive solution. If it involves swapping out 30 parts - not so much. 

Bob

> On Nov 12, 2014, at 5:50 PM, Perry Sandeen via time-nuts <time-nuts at febo.com> wrote:
> 
> Wrote: At some point we will get into hacking the main board
> to switch from 15 MHz to 10 MHz.
> 
> One doesn’t have to that if one uses the two IC divide by
> 1.5 circuit I offered the list. I specifically found it so I didn’t have to
> hack the innards. 
> 
> Wrote: The great news is the oscillator is 5 Mhz.
> 
> Don’t bet the rent on that. My early units have 10 MHZ Datum
> oscillators.
> 
> Bob’s point about getting the GPSDO’s if all cost the same
> is a good point.
> 
> Another point. At least on the older units I have: GPSDO,
> Rubidium, and Crystal oscillator, the output circuitry after the 15 MHz
> conversion takes place is the same. So if one hacks the 10 Mhz into the chain,
> all one has to do is remove or bypass the 15 MHz filter before the output.
> 
> Even if you don’t have the rubidium unit but have either/or
> GPDO or Crystal oscillator email me off list for the rubidium schematic as
> after the logic chips they use the same circuit.
> 
> Regards,
> 
> Perrier
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