[time-nuts] Are there SC-crystals out there in the wild that are not Overtone?

[Gerhard Hoffmann]

Am 27.02.20 um 17:45 schrieb Richard (Rick) Karlquist:
> OTOH, you could build a simple Colpitts
> oscillator and see where it oscillates.
> That's what they did back in the dark
> ages.
>
> Any time nut should be up for that.
>
5.000 MHz. That was easy. It used to be in something Colpitts-like

for 30 years, but did not age to its advantage like good Scotch.

I was just puzzled because I could not find the fundamental.

When the subharmonic is so far off as Bernd has said, then I could

well have searched a day with the network analyzer at 1 Hz receiver

bandwidth without finding it. I'll postpone that to the weekend.


Someone has reverse-engineered the whole oscillator:

< https://www.bartelsos.de/dk7jb.php/ocxo-morion-mv89a?download=118 >

Jörn seems to read the timenut list, HI!


cheers, Gerhard

(now I'll have to shovel some snow, first time for this winter!)






> Rick N6RK
>
> On 2/27/2020 5:35 AM, Bob kb8tq wrote:
>> Hi
>>
>> Ok, so just to run the math:
>>
>> 5 MHz / 2.9 = 1.724 MHz
>>
>> If the Q at the fundamental is 500K (a wild guess) then 1.724 MHz / 
>> 500,000 = 3.4 Hz
>>
>> In a world where a synthesized sweeper *might* be stepping in 10Hz 
>> steps, that’s an
>> easy one to miss.
>>
>> Bob
>>
>>
>>> On Feb 26, 2020, at 11:40 PM, Bernd Neubig <BNeubig at t-online.de> wrote:
>>>
>>> Hi Gerhard,
>>> I am rather sure that it is a 5 MHz 3rd overtone crystal.
>>> the resistance should be in the 80 to 110 Ohm range and Q about 1.5 
>>> million. You can see the resonance without ringing in a span of 100 
>>> Hz or smaller with a sweep time of 10 sec minimum.
>>> See attached the response of a 5 MHz SC3 crystal in HC-40/U package.
>>> Indeed the 5.45 MHz is the B-mode which has a temperature 
>>> coefficient of -30 ppm/K
>>> Because the crystal blank  has  a plano-convex shape. The overtones 
>>> are quite far away from 3 times or 5 times the fundamental mode. 3rd 
>>> overtone is about (rough guess) 2.9 time of fundamental mode.
>>> To find them you must really carefully sweep around a few 10 to 100 
>>> kHz span with slow sweep time a narrow bandwidth
>>>
>>> Regards
>>> Bernd
>>> DK1AG
>>>
>>> -----Ursprüngliche Nachricht-----
>>> Von: time-nuts [mailto:time-nuts-bounces at lists.febo.com] Im Auftrag 
>>> von Gerhard Hoffmann via time-nuts
>>> Gesendet: Mittwoch, 26. Februar 2020 01:42
>>>
>>> To get a first impression, I soldered the crystal to an SMA plug and 
>>> put it on an
>>> R&S ZVB-8 network analyzer and measured S11. I could see the 5 MHz 
>>> resonance
>>> as a 15 dB dip.  There was also a resonance at 5.45 and a smaller 
>>> one another 90 KHz
>>> higher. the +10% suggest that it is an SC cut.
>>> But I could not see anything at 1 or 1.6666 MHz, so it should be a 
>>> fundamental crystal?
>>> Is that common?
>>> I made most measurements at room temperature. I can turn the hot air 
>>> solder
>>> station down to 91°C which is not far away from the crystal's 87.7°C
>>> inflection point, and I could see some variation on the 5.45 MHz 
>>> resonance vs. temp.
>>> I must build a fixture for the hot air because the sweep time at 1 
>>> Hz bandwidth
>>> is close to eternal.
>>> Is the un-harmonicity (???) between fundamental and overtones 
>>> stronger with SC-cuts
>>> than normal AT? I also could not see anything at 15 MHz. Next I'll 
>>> make a board
>>> for the PI fixture as described by Bernd Neubig in his crystal 
>>> cookbook.
>>> BTW I could see some more dips with >= 10 Hz resolution. I hope that 
>>> does not mean
>>> that the ZVB needs service.
>>>
>>>
>>>
>>>
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>>
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