[time-nuts] Z3801A OCXO manual trimming

[Ed Palmer]

On 2018-03-03 3:56 PM, Tom Curlee wrote:

> What I don't understand is the purpose of what looks like another coil or heater wrapped around the Kapton printed circuit heater stuck to the inner case.  This second coil/heater is 2 layers of 1/8" thick red foam wrapped completely around the inner case, with fine copper wires wrapped over each layer.  At least I think there are wires on each layer.  This whole second heater is taped down and I don't want to dig any further until I know a bit more about what I'm doing or find that there isn't a trimmer on the double oven 10811 oscillators.

You might want to read the tear-down info here: 
http://www.realhamradio.com/GPS-oven-journey.htm .  The author suggests 
that this strange structure isn't a heater, but is just a way to 
thermally isolate the inside from the outside.  Seems a bit extreme, but 
HP sometimes did things like that.  Note that right at the bottom of the 
page, there's a link to another article where the fault is diagnosed and 
repaired.

> Any ideas on the purpose of the outer heater (or whatever it is)?  Does the double oven 10811 have a manual trimmer that I can adjust to bring the oscillator back to the center of the EFC range?

According to the tear-down, yes it does.

> Assuming that I can manually adjust the OCXO back into adjustment range, will there be any issues with the Z3801 performance, things like phase noise, short term stability, etc?

AFAIK, it's just a 10811 with extended EFC range, so I don't see why 
tweaking the tuning would compromise anything.

Ed