[time-nuts] Temperature sensors and bridge amps

jimlux jimlux at earthlink.net
Tue Nov 16 05:34:57 UTC 2010


Harry Brown wrote:
> Back in the early 80's I was working for a company making military 
> communication satellites.
> 
> The 5 MHz Oscillators used on the satellite were in a double oven 
> keeping the oven temp within 0.001 Hz C.
> 
> We could adjust the oscillator frequency for aging by ground commanding 
> a bank of relays controlled a D/A converter to adjust  the oscillator 
> frequency.
> 
> Lots of fun back then.
> 
> Any idea what is used now?

there's a variety of oscillators used on satellites these days. It kind 
of depends on the specific application.  For science satellites, a lot 
of stuff is done with two way ranging, so the onboard oscillator only 
needs to be good enough to allow it to acquire the signal from earth.

TCXOs are good for the 0.5 ppm sort of performance. Nice and low power.
OCXOs are somewhat better, at the cost of more power consumption
USOs (a OCXO in a vacuum bottle, with a very fancy crystal and 
electronics) are used where very good performance is needed.  ppb per 
year stability over time, 1E-12 over temp,  but volumes around a liter, 
mass around 0.5 kg and powers around a watt

There's development of a trapped mercury ion clock underway, which 
should improve performance by several orders of magnitude.

There are also flight qualified Rb and Cs sources being used, on GPS 
satellites among others.

There's also experimental stuff with disciplining non tcxo oscillators 
against GPS and similar schemes.  That should get performances 
comparable to other terrestrial GPSDOs




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