Can type xtal oscillator, thermal drift ntc or ptc.

[dr pepper]

I have a Ad9850 module off ebay. I put together a unit which contains the ad9850, a pic and a ds18b20 temp sensor, the whole thing I built in a crystal oven for stability.
The osc module is a vcxco theres a 4th pin, so I have connected this to one of the pots that you can adjust from the front of my mil xtal oven (I emptied it out).
I expected the oscillator to slow down as I heat up the xtal, it goes the other way, I thought mechanical resonance went down with temp as the xtal expands and grows lowering its resonance.
Can someone enlighten me.

Edit: sussed it, an xtal has a curve not a linear slope, the freq goes up as the oven warms, and then as it gets to temp comes back down again, I remember now your sposed to find the flatest spot at the bottom of the curve and run the xtal at that temp.

 

[cowboybob]

dr pepper,

Is that oven you have one of the old mil spec, calibration frequency sources?

It had like 6 (or so) nested ovens to keep a xtal osc at precisely the right temp to assure an exact output (at least in the late 1960s) of 10mHz plus or minus 1 count in the ones position?

They were used as sources to assure comms compliance.

 

[dr pepper]

Not quite, its a single oven, and the date codes are from the mid 80's.
Mechanically well made, but the circuit was pretty naff.
The type of thing you mention I dont think I'd butcher.

 

[Dean Huster]

Six nested ovens, Bob? Even the AN/URQ-10A or a Hewlett-Packard 106A (?) quartz frequency standarda only had one as I recall. There's a point where nesting becomes a problem, considering that each nested oven will have to be set for an even higher temperature than the oven in which it is nested. That means running a pretty hot crystal/oscillator circuit if you're going to be allowing for operation in the desert. Besides, there's a point where the additional ovens will provide no better temperature control than only two ovens, just because of circuit variances.

One way to maximize temperature and frequency control is to make sure that the crystal, crystal oscillator and one or two stages of buffering, power supply and oven temperature control circuitry are all in the oven together.