Using non-overtone crystal in overtone mode?

[Harold E. Johnson]

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.

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

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

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.

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.

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

 

[douglas dwyer]

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.

 

[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

 

[Don Klipstein]

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.

This reminds me of a colleague who can easily tell everyone
qualitatively that a situation deviates from theoretical ideals and as a
result (using my words and not his) "$#!+ (poop) will splatter!" But he
at least often in my experience have trouble saying this quantatively!

For one project, I decide to try something, and tell my boss what I am
trying. This colleague of mine says (using words of mine and not his),
"slop will spatter"! (As in light for adding optics to a light source for
a specific application. This application has multiple LEDs shining onto
an optical device with multiple elements.)
Boss tells me that what I delivered to him and he found working should
not have worked according to this colleague of mine, due to stray beams
forming. So what do I do - I send photos to the boss of the beam pattern
including the stray beams predicted by my colleague. I even named these
stray beams after my colleague. But they were minor due to most light
produced by the light source being on paths that resulted in adding to the
desired beam combination as opposed to the undesired stray beams.
Furthermore, my boss's industrial designer designed a baffling system
that blocked the small amount of light from the multi-element light source
that was on paths towards the stray beams as opposed to the desired rays
that were "on course" to be utilized by the multi-elemt optical assembly
as planned.

So beware that the situation may not be much worse than ideal when
someone can tell you how you are deviating from ideal!

 

[Don Klipstein]

---
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 ([email protected])

 

[John Fields]

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?

 

[Reg Edwards]

A solid slab of crystal naturally oscillates at frequencies at which one of
its three dimensions, length, breadth and thickness, is a mechanical
1/2-wavelength. It can easily be induced to oscillate at harmonics of the
fundamental.

It can also oscillate in one of several mechanical modes, eg., longitudinal,
breadth-wise or in torsion. And in shunt or series-resonant electrical
modes.

The circuit it is embedded in can encourage a preferred frequency. It is
easy to select harmonics. Self-preference is also given to the frequency
which has the highest Q, ie., the least mechanical loss. This is usually the
fundamental.

It does not oscillate EXACTLY at multiples simply because it has three
dimensions and Length, Breadth and Thickness slightly 'interfere' with each
other.

A poorly cut crystal, eg., lack of parallelism, at which there may be no
strong preference may jump erratically between two non-harmonically related
frequencies.

Frequency versus temperature curves depend on oscillation mode and on the
angle at which the slab is cut relative to the direction of the individual
crystals in the bulk material lattice as found by optical means. Cubic
curves are best because they contain a flat horizontal portion.

 

[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

 

[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]

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]

=======================================
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)