Using non-overtone crystal in overtone mode?

[douglas dwyer]

In message <OhfGOYBPeDJCFwJT@jmwa.demon.co.uk>, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> 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

 

[Harold E. Johnson]

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

 

[Robert Scott]

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.

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

 

[Ken Smith]

In article <1126ufulsdj5s93@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[....]

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.

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.


--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <11276jobn8vot2f@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[....]

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

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

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <112734jd5n2lf2f@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[...]

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:
http://literature.agilent.com/litweb/pdf/5965-7662E.pdf.

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.

--
--
kensmith@rahul.net forging knowledge

 

[RST Engineering (jw)]

Sorry, dude, 50 years of designing with crystals, right from when I ground
my first surplus WWII rock on a piece of glass with toothpaste as the
abrasive says that what the original poster asked is correct.

Will the harmonic be precise? No. Will it be "close", which is what the
original poster asked? You bet. Depending on the oscillator circuit, can
it be "pulled" on frequency? Perhaps.

But to say that the crystal doesn't resonate anywhere near the harmonic is,
as I said, bullpuckey.

Jim



"Terry Given" <my_name@ieee.org> wrote in message
news:keSUd.5425$1S4.590975@news.xtra.co.nz...

RST Engineering wrote:
That is total and absolute bullpuckey.

Jim

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

Cheers
Terry

 

[douglas dwyer]

In message <mj3Vd.8232$OU1.3254@newssvr21.news.prodigy.com>, Joerg
<notthisjoergsch@removethispacbell.net> writes

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.
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.
--
dd

 

[Joerg]

Hello Douglas,

Often cheaper to multiply up than buy an expensive 5th overtone that
was difficult to pull onto frequency and fussy to set up.

And these special cuts can indeed be fussy. They can also be a
procurement nightmare.

The exception would be current and size saving for some portables.

Even then it could be done. Besides the discrete solution there are
blazingly fast logic inverters such as the ALVC series. These are
usually under 20 cents and come in the super tiny TSSOP format. Now I
just wish they had unbuffered versions to do the oscillator part with.
If a 74HCU04 is needed for other jobs on the board it could run the
oscillator but for any reasonable speed these require more than 4V.

Regards, Joerg

http://www.analogconsultants.com

 

[Don Klipstein]

In article <ts6921d632jtuabnv9d0n9b0hv5mlb573i@4ax.com>, John Fields wrote:

On Tue, 1 Mar 2005 08:12:48 -0800, "RST Engineering \(jw\)"
jim@rstengineering.com> wrote:

Sorry, dude, 50 years of designing with crystals, right from when I ground
my first surplus WWII rock on a piece of glass with toothpaste as the
abrasive says that what the original poster asked is correct.

Will the harmonic be precise? No. Will it be "close", which is what the
original poster asked? You bet. Depending on the oscillator circuit, can
it be "pulled" on frequency? Perhaps.

But to say that the crystal doesn't resonate anywhere near the harmonic is,
as I said, bullpuckey.

---
Sorry, dude, no matter how much time you've got in, if you go back
and read my post, you'll find that I wrote:

"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.

Now suppose someone makes a crystal oscillate in some overtone mode that
the crystal manufacturer recommends against and is predicted to be
"inharmonic" but turns out to be only a few hundred or even sometimes a
few 10's of KHz from a multiple of a frequency that results from being
used as directed?

As I said in different words in a different post - correctly predicting
that $#!+ (AKA "slop") will spatter does not necessarily that much will
spatter nor that any will spatter far, and maybe in many cases it is
doubtful that both much will spatter and that much will spatter far.

- Don Klipstein (don@misty.com)

 

[Tim Wescott]

Tim Shoppa wrote:

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

 

[Larry Brasfield]

"Tim Wescott" <tim@wescottnospamdesign.com> wrote
in message news:112734jd5n2lf2f@corp.supernews.com...
....

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: http://literature.agilent.com/litweb/pdf/5965-7662E.pdf.

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.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[douglas dwyer]

In message <1109618629.998142.124510@o13g2000cwo.googlegroups.com>, Tim
Shoppa <shoppa@trailing-edge.com> 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

 

[douglas dwyer]

In message <1eb84d4a.0502281507.73ff7c41@posting.google.com>, Frank Moe
<moesenpeter@gmx.de> 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

 

[J M Noeding]

Hi

have been examining some surplus mobile telephone base station
equipment and discovered that the 70MHz to 455kHz mixers consists of
2x SA602. Since I've never seen an application using two such items,
my guess it for an image rejection type mixer.
Could somebody please guide me into some notes describing such mixer,
possibly using 2x SA602 (and a crystal osc)

Jan-Martin

---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

 

[Highland Ham]

have been examining some surplus mobile telephone base station
equipment and discovered that the 70MHz to 455kHz mixers consists of
2x SA602. Since I've never seen an application using two such items,
my guess it for an image rejection type mixer.
Could somebody please guide me into some notes describing such mixer,
possibly using 2x SA602 (and a crystal osc)
=======================================

Jan-Martin , With 2xSA602 ,are you sure there isn't a 10.7 MHz
'intermediate' IF as well ?

Frank GM0CSZ / KN6WH

 

[Andrew Holme]

J M Noeding wrote:

have been examining some surplus mobile telephone base station
equipment and discovered that the 70MHz to 455kHz mixers consists of
2x SA602. Since I've never seen an application using two such items,
my guess it for an image rejection type mixer.

An image rejecting mixer requires quadrature inputs (both signal and
LO), two mixers, and summation of the outputs i.e.

sin(A+B) = sin(A)cos(B) + cos(A)sin(B)

Also - you're unlikely to have image problems at the second mixer.

 

[J M Noeding]

On Mon, 07 Mar 2005 11:13:33 GMT, "Highland Ham"
<abcgm0csz.kn6whxyz@abcntlworldxyz.com> wrote:

have been examining some surplus mobile telephone base station
equipment and discovered that the 70MHz to 455kHz mixers consists of
2x SA602. Since I've never seen an application using two such items,
my guess it for an image rejection type mixer.
Could somebody please guide me into some notes describing such mixer,
possibly using 2x SA602 (and a crystal osc)
=======================================
Jan-Martin , With 2xSA602 ,are you sure there isn't a 10.7 MHz
'intermediate' IF as well ?

Frank GM0CSZ / KN6WH

Nope, it is shown as

http://www.noding.com/la8ak/12345/images/bd34-rx.jpg
This for NMT450, while earlier NOKIA NMT900 mobile phone BS used
21.4Mz IF as well as 455kHz, while modern 900mc GSM handsets now are
direct conversion. In the actual rig there is a 70MHz xtal filter as
well as 455kHz ceramic filters
The complete page (in Norwegian) is at
http://home.online.no/~la8ak/d28.htm

73, Jan-Martin LA8AK (ex GW5BFV)

---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

 

[Ken Smith]

In article <omu621p01vkm51l99jrvtold0pcgkt09rh@4ax.com>,
John Fields <jfields@austininstruments.com> wrote:
[..]

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. It's more like the slab of
crystal is vibrating like the drumhead of a steel drum with small
areas of the slab vibrating at higher frequencies, instead of the
entire slab virbarting at just one frequency.

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:



If you think about the top two lines of text in my little drawing. I
think it is obvious that if the maker thinned it down by one line of text
just as you come to the edge, that portion of the crystal would not work
well at this harmonic. This is what they do in crystals intended for
fundamental operation. It knocks that activity down by several dB at the
overtone. This makes it very unlikely that a simple oscillator will take
off at an overtone.
--
--
kensmith@rahul.net forging knowledge

 

[Bob Liesenfeld]

J M Noeding wrote:

Hi

have been examining some surplus mobile telephone base station
equipment and discovered that the 70MHz to 455kHz mixers consists of
2x SA602. Since I've never seen an application using two such items,
my guess it for an image rejection type mixer.

Could it be for dual diversity receive?