Using non-overtone crystal in overtone mode?

Overtone crystal cuts are not fundamentally different from fundamental crystal cuts, so to a 1st-order approximation they'll work. Crystals do have spurious responses that can cause mode jumping, and these responses don't necessarily map the same way the overtones do, so using a 20MHz crystal at 100MHz may or may not work, depending on the luck of the draw. Other than that I don't know of any differences.

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.

Tim, would a 100MHz oscillator module do for you? See DigiKey CTX318LVCT-ND, for example.

Cheers, Tom

In an AT cut crystal the overtone modes are close, but not exactly on, the odd harmonics of the fundamental. Furthermore, all of the literature that I've read on AT cut crystals reports that they vibrate in the bulk of the crystal, in shear mode -- see figure 7 here:

Perhaps you're thinking of SAW devices?

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

"Tim Wescott" wrote in message news: snipped-for-privacy@corp.supernews.com... ....

harmonics of the fundamental. Furthermore, all of

the bulk of the crystal, in shear mode -- see figure

One effect to watch out for with use of unspecified overtone modes is that the behavior of the resonator is not ideal; the presence or size of nearby spurs and the Q depend on how uniform the thickness is that determines frequency and the placement and size of contact metal. The wavelength is typically much less than the dimension along the non-shearing axis, so having a single mode of resonance near the nominal frequency or its overtones is not guaranteed, except by careful construction and verification. So, clearly, a guarantee about the behavior near the fundamental resonance cannot be extended to the overtone modes.

If I was trying to build a stable and pure oscillator operating at a crystal overtone, I would buy the crystal specified for the overtone I would be using.

harmonics of the fundamental. Furthermore, all of

the bulk of the crystal, in shear mode -- see figure

I pointed that out in a previous post. But hey -- wouldn't it be fun to have an oscillator that yodels?

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

Frank

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

That is total and absolute bullpuckey.

Jim

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.

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.

In message , Tim Shoppa writes

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

a CB xtal will probably operate on 100MHz, althouth I've only seen applications for 45 and 81MHz

-jm

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

Hello Jim,

Huh? See the 2nd paragraph (mode):

Regards, Joerg

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