[time-nuts] Airflow around oscillators.

[David Kirkby]

I am building a GPS locked oscillator and will have in the box the 
following.

1) GPS receiver

2) 24 V linear power supply I have had sitting here for ages - a use for 
it at last!!

3) PRS10 rubidium

4) 10811-60111 quartz

5) 2 x 7 Ah 12V sealed lead acid batteries.

6) Shera board, to lock the 10811 to either the rubidium or GPS 
(interesting to see what gives best performance)

7) A couple of DC-DC converters to give other voltages necessary for the 
Shera board. This seems more sensible than separate power supplies, due 
to my desire to have battery backup. I don't want a battery for +5V, 
another for -5V etc.

8) A small amount of control logic, to sequence the ovens on the quarts 
and rubidium, as I can't have both heating up at the same time, although 
they can both run together later.

I need to keep the batteries cool, so are planning on blowing cool air 
over them and around to the power supply.

I'm wondering if its best to try to reduce the airflow around the 
10811-60111 and PRS10 (rubidium) to a minimum necessary to keep the 
things within temperature, or is airflow over them not going to be an 
issue? That would make life a bit easier, if I can ignore that.

I'm also thinking of using a thermostatically controlled fan, in an 
attempt to keep the temperature inside the box a constant. The unit will 
*not* be run in a temperature controlled environment, but one in which 
there are quite large changes in temperature.

Whilst I don't mind experimenting with such things

a) Whether the theromostaticaly controlled fan gives smaller or larger 
changes in the rubidiums base temperature (it has a sensor which can be 
read.

b) What gives the best performance (10811 or PRS10)

c) What it is best to lock the 10811 to (GPS or PRS10)

I am not too keen on treating this lot as mechano and trying every 
possible combination of component placement. Once placed, they will stay 
there, with the exception of perhaps some thermal insulation and the 
location of a temperature sensor for the fan if used.

Any thoughts?

-- 
David Kirkby,
G8WRB

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/