[time-nuts] Mark - Reeves Hoffman OCXO

Murray Greenman murray at rakon.co.nz
Sun Jun 10 14:54:04 EDT 2007


Everyione else on the list seems to be paddling their own canoes lately
and may not have spotted your query.

Yes, you most surely can use an external EFC voltage to control this
device. You will need to learn what's connected inside, and I suspect
there will be a precision reference and resistor to the pin, and then
the user provides a resistor to ground on the outside. Find out by
measuring the open-circuit voltage, then by pulling the pin to ground
with a milliameter and determining what current flows. Then use Ohms Law
to work out the Thevenin equivalent source.

If the source impedance is fairly high, simply drive the oscillator EFC
from an external source. If it's lowish, consider putting a pot to
ground that puts the oscillator on frequency, and driving the pot/pin
junction with a low source impedance. I've taken this approach with the
Morion MV89.

Either way, the external drive will need very stable, noise free, and
use a very good reference.

There's another possibility I've not tried, and that's to use an
electronic resistor. I don't mean one of the steppable EEPROM type, but
simply a current mirror or transconductance amplifier.

Murray ZL1BPU

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