[time-nuts] Better option than oil

Murray Greenman denwood at orcon.net.nz
Tue Sep 20 18:19:49 UTC 2011

Folk looking for alternatives to dunking things in oil might consider trying 
a variant of the following technique which I have used with success:

The thermal stability of TCXOs and XOs can be improved considerably for 
experimental purposes by slowing down the thermal time constant between the 
device and ambient. A simple technique which I have used consists of a 
recycled polystyrene box (picnic box, frozen food or dry ice transporter) 
filled with dry sand. I place the device under test in a plastic bag or 
other small container sealed as far as possible to keep sand out, and bury 
it in the middle of the sand. The sand has a high thermal mass, and that 
combined with the polystyrene insulation gives the device a thermal time 
constant to ambient of many HOURS.

While I'd not suggest this is the right solution for an OCXO intended for 
use in free air, it is a way of achieving impressive short and medium term 
stability with simple unheated devices, especially if operated in a modestly 
controlled (e.g. air-conditioned) ambient environment, since the time 
constant is significantly longer than the ambient temperature cycling. The 
technique is almost good enough to remove diurnal ambient temperature 

Murray ZL1BPU

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