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 <[email protected]> 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:[email protected]] 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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