OK Rocco,
Now that I read the paper (URL below) on MESA crystals, I can comment
better. They are nothing more than very thin AT crystals (in the center of
a larger, thicker blank) and therefore have the normal AT cut
characteristics.
The reference you give below is a general datasheet from the manufacturer.
However, when crystals are manufactured they are made to a specific
requirement with regard to what is called "load". This would have been at
the request of the Engineer ordering the crystals. As explained in the
paper I referenced, crystals can be used either in a parallel resonance mode
or a series resonance mode.

Any crystal can be operated in either mode (any crystal can also be operated
in one of its overtone modes - I have done this), but to get the frequency
that it was manufactured for (and marked) you have to operate it in the mode
it was made for. Therefore, if you expect to get the frequency on the
crystal, you have to operate it in the correct mode. Just looking at the
crystal, you can not tell for which mode or load capacitance it was made.

If you put a crystal in an oscillator which runs the crystal in series mode
and the frequency is too low, then it was made for parallel operation and
needs a parallel type circuit like the Collpits. If a crystal is put into a
parallel mode circuit and it can't be brought down to the marked frequency,
then it is a series mode crystal. If I recall, the Pierce operates the
crystal in series mode. For reference, if I recall the difference between
the parallel mode frequency and series mode frequency is around 200-300 ppm.
for fundamental crystals in the 1-30 MHz range.

For lower frequency crystals it is common to specify in the range of 20-32
Pf load for parallel mode operation. There is no analogous "value" for a
series operated crystal...just saying "series" is enough.

Another consideration not mentioned in the overview paper that I reference
is that of power dissipation. Putting too much energy into the crystal will
heat the material and cause frequency drift. Though not discussed, I can
only speculate that the MESA construction requires a lower power operation
than non MESA because of the thin blank.
73, Steve, K,9.D;C'I


"Mario Bros" wrote in message
...
Hi Steve,
you see this link

http://daten.ws-mack.de/Freigabe/kvg.../Kat2/8_F4.pdf

My crystal is 155.520 Mhz.

I will make some test as you have suggested to me.

Merry Christmas for all.

IK6GQC Rocco


"Steve Nosko" ha scritto nel
messaggio
...
Do you know what load they are cut for? That osc is for overtone
operation
and those usually run the crystal in series mode.

Start using Google more... This may be just what you need.

http://www.sss-mag.com/pdf/saosc.pdf
I'm not familiar with MESA's, but If this is the crystal type, this may
help.
It is just for MESA resonators and appears to say they are series cut.
It
also looks like a good general reference on crystal characteristics as
it
shows the typical resonances at the overtones.

http://www.icmfg.com/crystaloscillatordata.html
If I thought they were parallel load xtals, I'd start with the
fundamental
Colpitts if they are parallel crystals, but a tuned circuit may help to
improve the phase noise.

73, Steve K,9.D;C'I



"Mario Bros" wrote in message
...
Hi folks,
I have acquired of the MESA Quartz Crystals to approximately 160 Mhz
fundamental AT.
Someone knows some circuit for their use?
73's de IK6GQC Rocco