[time-nuts] A fan for the Z3801A

Alberto di Bene dibene at usa.net
Mon Jul 28 09:40:40 EDT 2008


Murray,

   thanks for the advice.

Well, my intention was, as suggested by a private message, to use a 12V fan powered at 5V, so that it runs slowly and 
silently, not blowing external air into the unit, but just extracting the hot air from the inside.

  And given that the unit is placed in the basement of the house, with a change in temperature between the day and the 
night of no more than 1 Celsius, may be the use of the fan should not disturb the thermal regulation of the OCXO and the 
other temperature-sensitive devices, while at the same time lowering the working temperature of those hot ICs, thus 
prolonging (maybe) their life.

  Anyway I am open to comments and suggestions.    Thanks

73  Alberto  I2PHD
------------------------------------------

Murray Greenman wrote:
> Alberto,
> 
> I'm not much in favour of the idea of adding a fan (to any GPSDO, not
> just the Z3801A). While I've not tried it, there would be a risk of
> upsetting the stability of the unit, especially if the fan speed varied
> or the air flow changed for some other reason. If you could be sure that
> the airflow was steady and was not directed at the OCXO, it might be OK,
> but test it out.
> 
> In my experience with the Z3815A I noticed a marked change in frequency
> (it returned and settled after a while) when I turned the unit gently
> upside down, i.e. reversed the direction of convection.
> 
> It would be preferable, in my opinion, to simply improve the convection
> paths in your present setup.
> 
> As an aside, it is interesting to note the steady-state power
> consumption of the various units. The Z3801A is spec'd at 25W, the
> Z3815A (with hockey-puck oscillator) 35W, and at the other extreme, the
> Trimble NTGS50AA only 5W!
> 
> 73,
> Murray ZL1BPU





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