On Mon, 28 Feb 2005 13:29:15 -0800, RST Engineering (jw) wrote:

I don't know why off-the-shelf crystals are needed when Jan Crystal (Ft.
Myers FL) will make the crystal to your specifications in a few days for the
same amount of money. They can do fifth ot at 100 MHz. quite easily.

Jim

Jan's what I was about to suggest. I thought the rock I needed would
have been off the shelf, but they made it and sent the test results.
--
Best Regards,
Mike

In message .com, Tim
Shoppa writes
Are "overtone" crystals cut differently than "fundamental" crystals?
Or are they just specified differently?

In particular, say I took a garden-variety 20MHz fundamental
microprocessor crystal and instead used it at its fifth overtone,
trying to hit 100 MHz. The LC network is there to make sure that it's
on its fifth overtone. Will this "misuse" mean that the oscillator
will be harder to start up, less stable, more noisy, ???, than a
crystal oscillator made out of a real overtone crystal? I don't mind
if I "miss" 100 MHz by a several tens or hundreds of ppm, as long as
it's stable there.

If anyone knows of a place that ships off-the-shelf 100 MHz fifth or
seventh overtone crystals, I can avoid this whole exercise.... :-)

Tim.

Overtone crystals are mechanical resonators and the overtone shear mode
which has additional shear planes within the volume wont occupy exactly
the same volume as the fundamental so the frequency will not be exactly
3X or 5X the fundamental but approx 2000ppm high or low?
The fundamental crystal will not be so accurately polished or
dimensioned as the overtone so it will not go well if at all also it may
have higher levels of spurious.
--
dd

I read in sci.electronics.design that douglas dwyer
wrote (in )
about 'Using non-overtone crystal in overtone mode?', on Mon, 28 Feb
2005:
Overtone crystals are mechanical resonators and the overtone shear mode
which has additional shear planes within the volume wont occupy exactly
the same volume as the fundamental so the frequency will not be exactly
3X or 5X the fundamental but approx 2000ppm high or low?

I remember being told by a crystal 'expert' that with some cuts the
difference can be much larger than that. Is that so?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

In message , John Woodgate
writes
I remember being told by a crystal 'expert' that with some cuts the
difference can be much larger than that. Is that so?
Yes depends on electrode diameter plate diameter plate back (electrode
thickness) and parallelism. ie I would not be surprised at 10000ppm.
--
dd

Hi Doug, great to hear from you and the info in your posts. I'm currently
using a SAW at 660 MHz for the clock in a 9951 DDS. Actually, it's better
than my 200 MHz 7th overtone tripled to 660 with an MMIC although I do think
my MMIC tripler is most of the culprit.

Reason for the post, I think you've changed ISP's on me again, my mail to
you gets bounced. Would you pse address me a short note to the e-mail
address and give me the current one? That is, if it's not me you're trying
to get rid of!

Regards

W4ZCB

Harold Johnson wrote:

I'm currently
using a SAW at 660 MHz for the clock in a 9951 DDS.

Interesting factoid: I was looking to experiment with 100MHz
oscillators largely as a clock source for my own AD9951 experimentation
(using the AD9951's built-in PLL multiplier at 4x). I was hoping to
experiment a bit with 20 MHz crystals I already had in hand before
ordering some "real overtone" crystals cut just for me. I've been
looking at AD app note AN-419 and it's Butler oscillator, in
particular, although the clock input of the AD9951 probably has
different requirements than the AD9850 targetted in AN-419.

Does the AD9951 really work at 660MHz? I thought it was only good to
400MHz...

So far my experimenting has used the on-chip oscillator at 25MHz and
the PLL at 16x to get to 400MHz.

Actually, it's better
than my 200 MHz 7th overtone tripled to 660

We bandied about "non-harmonic" relations here but how you get from 200
to 660, I don't know.

Tim.

"Tim Shoppa" wrote in message roups.com...
Are "overtone" crystals cut differently than "fundamental" crystals?
Or are they just specified differently?

In particular, say I took a garden-variety 20MHz fundamental
microprocessor crystal and instead used it at its fifth overtone,
trying to hit 100 MHz. The LC network is there to make sure that it's
on its fifth overtone. Will this "misuse" mean that the oscillator
will be harder to start up, less stable, more noisy, ???, than a
crystal oscillator made out of a real overtone crystal? I don't mind
if I "miss" 100 MHz by a several tens or hundreds of ppm, as long as
it's stable there.

If anyone knows of a place that ships off-the-shelf 100 MHz fifth or
seventh overtone crystals, I can avoid this whole exercise.... :-)

Tim.


Tim,

to get optimum performance one would grind the 100MHz 5.OT finer or
even polish it, and the thickness of the electrodes might be different
to get optimum Q.
But you should be ok by using a 20MHz fundamental in its 5th.

There are also manufacturers that make 100 in fundamental (up to about
200MHz), and many should have 100 in 5th as standard part...

Frank

In message , Frank Moe
writes
There are also manufacturers that make 100 in fundamental (up to about
200MHz), and many should have 100 in 5th as standard part...
High frequency fundamentals are real and can be purchased to at least
250MHz note they are expensive, their Q which is ultimately material
related reduces with increased frequency (loss is per cycle) such that
it may be no higher than a SAW resonator . Still better than a SAW as
the temperature coefficient for the SAW only has the linear cancelled
whereas the AT cut has the parabolic term cancelled.
Finally the 5th overtone will only pull 1/25 times the fundamental.
Finally finally the SAW can be run at much higher power levels so noise
floor is much better.
Finally finally finally a SAW needs a mask which gives a high up front
cost and lead time.
The difference in frequency for overtone /X fund may be much more than
2000ppm where the plate is not very parallel and the plate back and
electrode diameter non optimum. Beware AT cut strip crystals ie a long
section of a circular diameter these may not like overtone operation.



not pull with external reactance change perhaps a byt
--
dd

Hello Tim,

As Douglas said the frequency may be a bit off unless you get a crystal
made for 5th. An alternative for the 20MHz garden variety would be to
make a 20MHz oscillator, run it into a fast gate and fish out the 5th
the old fashioned way, with an LC circuit. Then run that through a gate
again if needed.

Regards, Joerg

http://www.analogconsultants.com