[time-nuts] is there a "best bet" advanced hobbyist buildable GPSDOdesign?
steveheidmann at yahoo.com
Thu Dec 13 18:08:51 EST 2007
For low noise Zetex has a nice roll your own option, AN51
Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
Scott Burris wrote:
> Continuing the design discussions, anyone have opinions about powering
> the HP 10811 oscillator?
> I'm thinking that you want voltage regulators that are pretty quiet so
> as to minimize jitter introduced
> via the power supply. To that end, I'm looking at a LT1761 for the +12v
> OSC voltage and an LT3080
> for the 24v heater supply.
How does the output noise of an LT1761 compare with the 5uV rms (100Hz
to 10KHz) output noise of the recommended LM723 regulator?
> In reading the 10811 manual, the heater and oscillator are isolated, yet
> the example power supply ties
> both together in a common ground. That certainly would make things
> simpler, as a 24VCT transformer
> could be used, and +12 and +24 volts could be made pretty naturally that
The important thing is to regulate the oscillator supply at the
oscillator supply pins and the oven supply at the oven supply pins.
With judicious application of Kelvin sensing the oven and oscillator
supply grounds can be connected together (or heater GND = -12V, Heater
supply = +12V) without significant interaction between the oven current
variations and the oscillator supply voltage. Similarly use Kelvin
sensing techniques (just use a conventional difference amplifier) to
control the EFC voltage between the EFC input and the common oscillator
EFC ground point within the OCXO.
> How important in a GPSDO application is it to keep these two sections
> completely isolated? I figure I would
> either have to use a small HF transformer with a chopper circuit or a
> separate 60hz transformer for the second
Don't add noise unnecessarily unless you can live with the resultant
OCXO sidebands (or the cost/complexity of a suitable filter to remove
high frequency noise from the power supply).
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