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

"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

On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:


IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE
means! Here I thought it was a quality mark). Etc.

Dialog news reader's tip popped up to say that CE is "creative
editing". It doesn't KWTF IDNKWTFIAS is, but I got everything but
the IAS part.

--
Best Regards,
Mike

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

Active8 wrote:

On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:


IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE
means! Here I thought it was a quality mark). Etc.


Dialog news reader's tip popped up to say that CE is "creative
editing". It doesn't KWTF IDNKWTFIAS is, but I got everything but
the IAS part.

IDNKWTFIAS: I Don't Know What I Am Saying.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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

On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:

IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE
----------
means! Here I thought it was a quality mark). Etc.

I Do Not Know WTF I Am Saying?

Thanks,
Rich

Rich Grise wrote:

On Mon, 28 Feb 2005 12:07:49 -0800, Tim Wescott wrote:

IIRC Digi-Key has 100MHz crystals, but I may be remembering 100MHz
oscillators. YMMV. IDNKWTFIAS. Caviat Emptor (so _that's_ what CE

----------

means! Here I thought it was a quality mark). Etc.


I Do Not Know WTF I Am Saying?

Now Rich, that's being awfully harsh on yourself.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"John Fields" bravely wrote to "All" (28 Feb 05 14:34:30)
--- on the heady topic of " Using non-overtone crystal in overtone mode?"

JF From: John Fields
JF sci.electronics.components:12029 rec.radio.amateur.homebrew:8635

JF Check out "Chladni patterns" if you're interested.

I've done some putzing with crystals. What frequency say would a
100.3MHz xtal in series with a 100.1Mhz xtal settle on? 100.2Hz?

A*s*i*m*o*v

.... It's kind of fun to do the impossible... -Walt Disney

That is total and absolute bullpuckey.

Jim


---
You can use a fundamental mode crystal as an overtone oscillator, but
even if you can get it to oscillate, it won't be generating an
overtone at 100MHz, since overtone modes of oscillation aren't
harmonically related to the fundamental.