[time-nuts] What type of Crystal?

[Magnus Danielson]

Ed Palmer skrev:
>    The recent discussion regarding the type of crystal in the HP 10544A
>    brought this question to mind.  We're always coming across unknown
>    oscillators.  Usually we can figure out the pinouts and voltages.  Then
>    we can measure stability, aging, etc.  But are there any tricks to
>    figure out what type of crystal is in the oscillator?  How can you
>    detect the differences between AT, BT, SC, etc?

One thing which may be a hint is to look at what frequency they have 
cold, the detuning they have at room temperature is quite a good hint. 
This works best for OCXOs, since TCXOs at these frequencies usually is 
AT cut.

>    I think that AT crystals have a broader tuning range than SC and that
>    when warming up AT crystals tend to overshoot the final frequency and
>    fall back.  Are these generalizations correct?  Are there other tricks
>    to help differentiate the crystal types?

The overshot by itself may not be a good indicator. An SC with wrong 
temperature may exhibit overshot as well.

SC cut 10 MHz seems to be about 200 Hz low at room temperature. Don't 
recall the number for AT cut, but I think I saw something like 1 kHz or 
so recently. Need to test to be sure.

Cheers,
Magnus