[time-nuts] frequency reference for portable operation

[Magnus Danielson]

On 11/03/13 21:20, John Miles wrote:
>>>
>>> With most modern lightweight Rb's the OCXO is integrated into the same
>> heater block as the physics package. That makes it a bit tough to heat one
>> without heating the other. .
>>
>> On LPROs the OCXO sits on the opposite side of the board.
>
> Pretty sure that's not an OCXO.  If it is, it's a tiny one that will warm up
> very quickly.  I doubt it's even a TCXO, though.

Considering that the sweeping ranges +/- 15 ppm, it needs to be pretty 
good at least. TCXO is doable and the OCXO does not need to be very 
advanced. There is a heat-sink on the crystal assembly. It would make 
sense if it is an OCXO as the surrounding would be on the hot side while 
operating, so increase heat dissipation in order to keep it in balance 
would make sense.

The fact that we don't know the details is a side-effect of not 
reverse-engineering them properly.

> Of the Rb standards I've seen, only the PRS-10 and HP 5065A use OCXOs.  I'd
> assume that the old-school Tracor and R&S models also used OCXOs, but for
> the cheap telecom modules it would have been seen as a waste of money.

The R&S XSRM has an OCXO, so does my russian one.

> Also, the HP 5065A has separate ovens for the lamp and resonance cell, but I
> believe the smaller units use a single heater for both.  They won't lock
> until the heater is up to temperature.

You need to keep two different temperatures of the lamp (~70) and cell 
(~110), unless you tweaked it with buffer gas, which might be what they 
have done.

Cheers,
Magnus