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
variation.
73,
Murray ZL1BPU
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