Magnus Danielson wrote:
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.
Yes, I should have specified that I was talking about OCXOs. Since a
TCXOs purpose is to compensate for temperature changes, the concept of
'warmup' is a bit of an oxymoron.
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.
A defective oven controller could certainly confuse any attempt to
characterize an oscillator. Let's assume that - as far as we can tell
- the oscillator is working properly.
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.
I happened to record the startup performance of an HP 10544A. It
started out ~1100 Hz low. I was initially worried that it was
defective, but it was fine once it warmed up. It also appeared that
the amount of frequency overshoot was dependent on the oven voltage. I
want to investigate that more on various oscillators.
Ed
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