[time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
jimlux at earthlink.net
Fri Jun 2 19:02:40 EDT 2017
On 6/2/17 2:51 PM, Donald E. Pauly wrote:
> This is an improvement of 476 to 1. You apparently have not thought
> thru what improvements are possible with thermal coolers/heaters.
> Among these is near instant warm up and greatly reduced power for
> thermal management.
without getting into the whole crystal issue, one of the advantages of a
heater is that it can be VERY simple (and hence reliable, just on a
parts count basis). With a decent package, once it's hot, the power
required to keep it hot can be quite low.
With a heat/cool, you need to be able to have a bipolar supply to the
peltier device, and they're not particularly efficient (that is, to
extract 1 Watt of heat, you're putting in significantly more than 1 watt
of DC, and rejecting 1+X watts to the outside world.
And then, if you use a linear power supply/amplifier to drive the
device, that is probably a class A device, and somewhat lossy. A
switcher would be more efficient, but then you have the problem of
switching noise, in close proximity to the crystal. You could put a big
low pass filter in, but now you're adding even more components.
There are undoubtedly some cases where the thermoelectric scheme would
work better - for instance, you have a system with a TCXO and it's
really set up for the TCXO to be at 25C, and you want to regulate that.
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