Hi Bob

I've seen this topic discussed here before and it does seem to raise some
quite strong emotions and there does seem to be some confusion.

I can remember quite clearly, historically at least,  5MHz being commonly
promoted as the optimum frequency for crystal  oscillators on the basis that
5MHz crystals had this "sweet spot",  presumably when it came to temperature
stability.
An online search today hasn't been very forthcoming and unfortunately  most
of my reference library remains in storage, so I can't  provide instant
references, but I know I've also seen this in print  and can still envisage the
graphs used to demonstrate it.

The nearest to a current reference I've found is this comment from Enrico
Rubiola on page 156 of "Phase Noise and Frequency Stability in
Oscillators".........
"The process described relies on the ability to estimate the resonator's
quality factor. Experience indicates that the product voQ is a technical
constant for piezoelectric quartz resonators, in the range from 1 x 10^11 to 2
x  10^13. As a matter of fact, the highest values are found in 5MHz
resonators.  ............."

I have no axe to grind on this, aside from willingly admitting to  being
one of the confused:-), but if this is a misconception is it possible to
address why such a situation might have arisen?

Regards

Nigel
GM8PZR

In a message dated 03/11/2013 01:46:01 GMT Standard Time, lists@rtty.us
writes:

Hi

I believe that you are talking to two very different  groups, one who
actually design the crystals and the other who use the  products that are
designed. One is talking about what they can buy, the other  is talking about what
could / could not be done and why.

Bob

On  Nov 2, 2013, at 8:22 PM, Tom Knox actast@hotmail.com  wrote:

obviously extremely educated on the subject. So why is there some  disagreement
in two very knowledgeable groups?

that will accept a 0.55”  max diameter blank.

was adopted over 3MHz simply because 5MHz  multiplies to other commonly
used frequencies with greater ease. I think the  top frequency standards have
evolved to 5MHz Third Overtone SC cut crystals  for a reason. The evolution
has gone on from the days of Tesla and improved  greatly during the glory
days of Quartz in the years leading up to atomic  standards with countless
hours of experimentation and research. Those lessons  learned are constantly
examined through the lens of the latest  science.  I may be wrong, but I have
not heard of any extreme  design prototype quartz oscillator with superior
Phase Noise and Stability.  Our house standard F1 a cesium fountain is used
roughly one month every few  months to characterize roughly 12 5071A cesium
standards steering about 5 MHM  2010 cleaned up with a number of 8607 option
08 oscillator. (The equipment  choices are not a recommendation or
endorsement, and there are  po

products.) But the oscillators selected  are 5MHz third Overtone SC cut.

engineering

all of

performance,

mode,

Now,

people

On

operated  at

A

fundamental, a

influence

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Hi

Rubiola is looking at resonators he can buy off the shelf. They are constrained by the commonly available packages. The Q x F product does not suddenly stop going up at 5 MHz. There is good documentation that it keeps on going as the frequency goes down. Is Q everything - of course not. However if you wanted a much higher Q crystal than the 5 MHz, it could be built if you had the time and the money.

Bob

On Nov 3, 2013, at 7:58 AM, GandalfG8@aol.com wrote:

Bob, et. al.,

Lots of opinions in this discussion, but none of it discusses the elephant in the room affecting todays' vendors:

Random crystal instability versus manufacturing techniques.

I can buy oscillators from multiple vendors that have -115dBc at 1Hz or better and noise floors of -182dBc. That technology is well understood and has been mature for a very long time and to me its boring. Recently Ulrich Rhode even had a great article in the Microwave Journal detailing how exactly to build one of those units.

But what does it help me to have -115dBc if the darn thing jumps 50ppt every two to three days??

Crystal jumps are the biggest menace facing users of crystals/oscillators today and so far I have never been given a reasonable explanation from any of the vendors out there what causes it and how to avoid it or how they plan to address it.

In fact no vendor we know tests for it to levels of sub-ppt over days which is what is necessary for any disciplined application as disciplining will clearly show even the smallest crystal jumps. Almost every vendor will do a frequency test only, where a phase test would be needed.

Users of crystals/oscillators are left with doing an exhaustive yield test during burn-in to find bad crystals. We test our boards for 3 days and more to weed out jumpy crystals, and its a pain and very expensive to have to do this on finished goods as rework is in order for units that fail.

The results are staggering, some vendors consistently have jumpy product, others consistently have excellent product, all have at least occasional batches that are worse to far worse than standard deviation. Some are so bad that one batch may yield 95% and the next batch of the same exact product will only yield 50% or less!

I think this is the area of Quartz processing that has the least amount of research invested into it, and as anyone that has seen their Z38xx unit jump up and down in phase can attest to its a menace and can ruin one's day. I wish there were something besides yield testing that can be done to avoid manufacturing and shipping bad crystals to integrators. BVA seems to be one of those solutions, but how many BVA's have we seen in products that cost $400 retail??

Bye,
Said

On Nov 3, 2013, at 5:09, Bob Camp lists@rtty.us wrote:

Thanks Jackson, I think I have seen that lately, I thought that was a GPS problem related to the transition between holdover and locked but I was unable to reproduce it with a GPS simulator. It is really pronounced on the C-Mac in the unit.

Thomas Knox

On Sun, 3 Nov 2013 09:33:57 -0800
Said Jackson saidjack@aol.com wrote:

Could these be related to frequency dips?
Or radiation dependent jumps of unswept crystals?

Well one of our problems with quartz oscillators these days is,
that most of the knowhow is at the manufacturers behind locked doors.
It's quite hard to come by some good knowlege how to build crystall
oscillators these days. The good books have been written 20-30 years
ago and have been out of print for nearly as long.
I talked with some of the people who are kind of famous in the field
at the EFTF in Prague this summer, and half of them agreed, the other
half was more like "that's a solved problem" and "look for more intersting
problems to solve than crystal oscillators".

Doing research in this kind of enviornment is difficult at best.
Getting results out of one manufacturer is even harder.

Well, considering that a BVA costs at least 10 times as much...

		Attila Kinali

--
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
-- The Habits of Highly Boring People, Chris Sauve

Hi

Given that a full blown electroless BVA crystal typically  costs > $900 a piece, you are unlikely to find them in sub-$400 oscillators. There is pretty good evidence that they also can have jumps that need to be screened out….

Testing wise, looking at any part with a 2 to 5 ppt ADEV for sub 1.0 ppt max limit issues it not going to be very practical. You would simply reject all the product. The practical testing limits are going to be very much constrained  by the same things (wander / random walk / flicker noise)  that drive ADEV. If you want a 1 ppt test (resolution / limit / fit or what ever), then your ADEV probably should be 0.1 ppt or less. That’s a spec that will cost you some extra money.

Bob

On Nov 3, 2013, at 12:33 PM, Said Jackson saidjack@aol.com wrote:

Said Jackson posted:

Are you including both phase jumps and frequency jumps together?
Is one more or likely to happen than the other?
Is it mostly a jump that effects just the phase or freq, or is there
everything in-between, jumps that effects both phase and freq at the same
instant in time also just as likely?

We all know each effects the other, but that is only over time,
instantaneously and over short time spans phase and freq jumps are separate
things and maybe from different causes.
A true phase jump causes only a one cycle freq error and a true freq offset
jump does not cause an instantaneous phase jump.

If the main causes of random freq jumps and random phase jumps are from
different things, then with a high speed, high resolution detector,
I wonder if knowing which event has really occurred, that then some
correction compensation could be applied that does not effect the other.

An Oversimplified example;
A Phase lock loop does not care what the instantaneous freq is, and a true
Freq Lock loop does not care what the phase difference is.
With a DDS, one can change the freq without causing a phase step or it can
cause a phase step, without causing a freq offset.
With two variables (instantaneous phase and freq offset control) and two
unknowns (instantaneous jumps in either), couldn't one apply a correction to
the right place for any random step error that occurred?
It would depend if the errors are caused by true independent random fast
jumps or just slowly drifting interacting changes.

ws

Bob, et. al.,

Lots of opinions in this discussion, but none of it discusses the elephant
in the room affecting todays' vendors:

Random crystal instability versus manufacturing techniques.

I can buy oscillators from multiple vendors that have -115dBc at 1Hz or
better and noise floors of -182dBc. That technology is well understood and
has been mature for a very long time and to me its boring. Recently Ulrich
Rhode even had a great article in the Microwave Journal detailing how
exactly to build one of those units.

But what does it help me to have -115dBc if the darn thing jumps 50ppt every
two to three days??

Crystal jumps are the biggest menace facing users of crystals/oscillators
today and so far I have never been given a reasonable explanation from any
of the vendors out there what causes it and how to avoid it or how they plan
to address it.

In fact no vendor we know tests for it to levels of sub-ppt over days which
is what is necessary for any disciplined application as disciplining will
clearly show even the smallest crystal jumps. Almost every vendor will do a
frequency test only, where a phase test would be needed.

Users of crystals/oscillators are left with doing an exhaustive yield test
during burn-in to find bad crystals. We test our boards for 3 days and more
to weed out jumpy crystals, and its a pain and very expensive to have to do
this on finished goods as rework is in order for units that fail.

The results are staggering, some vendors consistently have jumpy product,
others consistently have excellent product, all have at least occasional
batches that are worse to far worse than standard deviation. Some are so bad
that one batch may yield 95% and the next batch of the same exact product
will only yield 50% or less!

I think this is the area of Quartz processing that has the least amount of
research invested into it, and as anyone that has seen their Z38xx unit jump
up and down in phase can attest to its a menace and can ruin one's day. I
wish there were something besides yield testing that can be done to avoid
manufacturing and shipping bad crystals to integrators. BVA seems to be one
of those solutions, but how many BVA's have we seen in products that cost
$400 retail??

Bye,
Said

Hi Warren,

On 11/03/2013 08:55 PM, WarrenS wrote:

A jump in frequency will cause the phase to go parabolic as it
integrates the frequency difference from the previous rate. Eventually
the PLL will react and hunt it it. Sluggish PLL will let the jump cause
a larger phase deviation than a quick PLL, but that is expected.

That type of phase-jump sounds like a support-oscillator having issues,
possibly with not sufficient suppression of other oscillating modes  of
the crystal.

With oven crystals, there is the effect of the oven as it gets a
heat-bump och chill-bump that it takes time for the oven control to
react to it. During that time, the thermal sensitivity of the crystal
(complex issue as it is) will cause the crystal to run higher or lower
than intended, and when the oven balance up again the frequency will be
about where it was before, but as you integrate the frequency deviation,
you have a phase-step in either direction. This phase-step is then being
tracked in by the PLL if you have one. I know of only two oscillator
products (from the same vendor) that have been trying to address this
issue. It's an important aspect, as today we work with stable phase
rather than stable frequency, yet many of our stabilization techniques
is aimed at stable frequency, which is a step in the right direction. To
make things worse, we want stable phase in challenging environments
where particularly size is an issue.

Good idea. Keep monitoring the events and their characteristics and you
might find out.

I would say they have different origin. Also notice how a PLL or other
control-loop can change the characteristic of a behavior, so you need to
understand what processes does to the shape in order to draw conclusion
of phase, frequency, drift step, ramp or whatever.

For a control-loop, you could naturally monitor the shape of the phase
detector deviation and draw conclusion about what just happen to your
oscillator (or input). You need to compensate or consider what the loop
does to the shape. Recording of both phase and frequency to record the
state of the loop  will aid significantly.

Cheers,
Magnus