[time-nuts] Insulating OCXOs

Murray Greenman denwood at orcon.net.nz
Thu Sep 15 05:53:04 UTC 2011

Many OCXOs, and definitely the CMAC (now RAKON) STP2145A, use ambient 
compensation technology. It is not possible to place the heater, the crystal 
and the temperature sensor in exactly the same place, and consequently there 
will be a thermal profile within the OCXO which depends on the oven design 
and the external environment. The ambient compensation corrects for this 
effect. (The temperature is measured inside the unit in two places in order 
to determine the thermal profile, and a calibrated amount of  this 
differential measurement is used to correct the oven control).

If, by lagging the OCXO, you change the thermal profile, which you will, the 
internal compensation set during calibration will be compromised. This will 
make the OCXO more sensitive to changes in ambient temperature than it 
should be.

Whilethis may not apply to double-oven oscillators, I still don't beleve it 
is a good idea to lag them.

You achieve nothing useful by reducing the power consumption of the OCXO 
through lagging: place the OCXO where it can have modest convection, but no 
draughts or insulation, and preferably no undue heating from the nearby 

Murray ZL1BPU

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