Using non-overtone crystal in overtone mode?

I read in sci.electronics.design that Terry Given wrote (in ) about 'Using non- overtone crystal in overtone mode?', on Tue, 1 Mar 2005:

Year 2005. (;-)

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Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
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I read in sci.electronics.design that douglas dwyer wrote (in ) about 'Using non-overtone crystal in overtone mode?', on Mon, 28 Feb

2005:

I remember being told by a crystal 'expert' that with some cuts the difference can be much larger than that. Is that so?

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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

Honestly John! That should be AMMV.

--- Sorry, dude, no matter how much time you've got "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."

and that you replied with:

"That is total and absolute bullpuckey."

Notice that I didn't say "near", I said "at".

If you can find fault with anything I wrote in that post, I'd appreciate specific criticism instead of that broad brush you painted with.

-- John Fields

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.

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

Tim.

The promulgation of a 'horrible hybrid' is justified in pursuit of a whimsical coincidence.

--
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 , Frank Moe writes

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

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dd

In message , John Woodgate writes

Yes depends on electrode diameter plate diameter plate back (electrode thickness) and parallelism. ie I would not be surprised at 10000ppm.

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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

There is a related phenomenon in the field of piano tuning. It has long been known that overtones (called "partials" by piano people) of piano notes are not exactly related to pitch of the fundamental frequency by whole numbered ratios. Instead they are related by factors like

1.000 2.003 3.007 4.018 5.039 6.092 7.211 etc.

The amount by which this series deviates from the ideal whole-numbered ratios is called "inharmonicity" and it differs from one string to another. The stiffer the string, the more inharmonicity. Long thin strings, as are found on harpsichords, have almost no inharmonicity. Short strings in the highest section of the piano have the most inharmonicity. Since one of the goals of piano tuning is to make partials of different notes come out the same, this phenomenon of inharmonicity makes piano tuning inherently more difficult than instruments that have no inharmonicity, like pipe organs.

What is perhaps more like quartz crystals is carillon bells. They are tuned at the factory, and each partial is tuned independently and separately by grinding away metal from different levels on the bell. In view of these related phenomena, it is no wonder that overtones of quartz crystals are independent of each other and from the fundamental.

-Robert Scott Ypsilanti, Michigan

In article , Tim Wescott wrote: [....]

There is a whole science of crystals all on its own. When they make a crystal they make a thin disk of material. You would normally expect the edge of the disk to simply be at right angles. Instead it looks like this:

*********************** * * * * *************************

The exact angle and depth of that chamfer is how they control which overtones are selected for and which are supressed. In fundamental crystals, the maker usually grinds the chamfer so as to reduce the 3rd harmonic responce.

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kensmith@rahul.net   forging knowledge

In article , Tim Wescott wrote: [....]

No, it isn't fun. Trust me :<

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kensmith@rahul.net   forging knowledge

In article , John Fields wrote: [..]

No, its more like a jello when you jiggle the dish side to side. The main action of an AT cut is shear mode. In the harmonics, the motion looks kind of like this:

In article , Tim Wescott wrote: [...]

Yes

In the ideal AT cut crystal "c mode" shear is the only activity. In the SC cut, the "b" and "a" modes appear. The extra complexity of the mode selection circuit is part of the reason that SC based OCXOs cost so much.

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kensmith@rahul.net   forging knowledge

OK, silly I know, but I cant figure out YMMV...

OTOH, WTF, IAAR

Cheers Terry

sorry dude, 50 years of IEEE UFFC papers suggest *you* are wrong. I was surprised when I learned this too.

Cheers Terry

Hello John,

When you look at older (pre-PLL) VHF communication gear of the more professional kind they didn't use 5th or higher overtones but employed frequency multiplier stages. For good reason, one being the offset you had mentioned. I'd never run a crystal on its umpteenth harmonic and always designed in multiplier stages like the radio folks did. With today's cheap logic chips that doesn't even cost much in extra parts.

Look on the bright side. Some of us, including me, didn't know the expression "bullpuckey". I got a kick out of it.

Regards, Joerg

The built-in multiplier is quite noisy and makes the 9951 run terribly hot.

Yes, if you DON'T use the on board multiplier. I've had it to 750 MHz just to check it since I had heard of some DL's overclocking it to that frequency. Properly heat sunk to the eval board, and without the multiplier, it's cool as a cucumber. AD rates it only to 400 MHz but a sample of 6 units all operate well at 660 MHz.

Well, this one is a 220 MHz 7th overtone from ICL specially surface treated for low noise and operating in a Stephensen bipolar/FET Butler. But as I mentioned to Doug, afraid my MMIC tripler makes a bad job of the 660 output despite a 3 pole final filter. The SAW is not near the Q of the crystal, but the SNR is much better.

Regards

W4ZCB

In message , Joerg writes

Often cheaper to multiply up than buy an expensive 5th overtone that was difficult to pull onto frequency and fussy to set up. The exception would be current and size saving for some portables.

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dd