[time-nuts] What type of Crystal?

[Ed Palmer]

My apologies to the list for the poor formatting on my previous 
message.  I'm having trouble getting Thunderbird to send a message with 
formatting that the server will accept.  Let's see what it makes of this.

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