[time-nuts] The 5MHz Sweet Spot
GandalfG8 at aol.com
GandalfG8 at aol.com
Sun Nov 3 12:58:24 UTC 2013
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 at 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 at hotmail.com> wrote:
> From reading your past posts I must respect your opinion. Your are
obviously extremely educated on the subject. So why is there some disagreement
in two very knowledgeable groups?
>
> Thomas Knox
>
>
>
>> From: lists at rtty.us
>> Date: Sat, 2 Nov 2013 18:44:18 -0400
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] The 5MHz Sweet Spot
>>
>> Hi
>>
>> The only thing that the 5 MHz 3rd crystal is “optimum” for is a holder
that will accept a 0.55” max diameter blank.
>>
>> Bpb
>>
>> On Nov 2, 2013, at 6:06 PM, Tom Knox <actast at hotmail.com> wrote:
>>
>>> Mike I think we must be talking to the same smart people. I think 5MHz
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
>>> ssibly m
>>> any product that could meet or exceed the performance of these fine
products.) But the oscillators selected are 5MHz third Overtone SC cut.
>>>
>>> Thomas Knox
>>>
>>>
>>>
>>>> From: mfeher at eozinc.com
>>>> To: n1hac at alum.dartmouth.org; time-nuts at febo.com
>>>> Date: Sat, 2 Nov 2013 09:50:50 -0400
>>>> Subject: Re: [time-nuts] The 5MHz Sweet Spot
>>>>
>>>> Exactly - I mentioned this on here about 3 years ago and all of the
>>>> self-proclaimed geniuses poo-pooded it. I was told early in my
engineering
>>>> career in the early 70's, by a very smart man, when I thought I had
all of
>>>> the answers, that considering all of the trade-offs regarding
performance,
>>>> around 3 MHz for a crystal is best, operating in the 3rd overtone
mode,
>>>> hence the slow progression from the 1 and 5 MHz standards to 10 MHz.
Now,
>>>> getting close to 70, I just see what I can learn from all the "smart"
people
>>>> on here, and keep quiet most of the time. Regards - Mike
>>>>
>>>> Mike B. Feher, EOZ Inc.
>>>> 89 Arnold Blvd.
>>>> Howell, NJ, 07731
>>>> 732-886-5960 office
>>>> 908-902-3831 cell
>>>>
>>>> -----Original Message-----
>>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
On
>>>> Behalf Of David McGaw
>>>> Sent: Saturday, November 02, 2013 1:30 AM
>>>> To: Discussion of precise time and frequency measurement
>>>> Subject: Re: [time-nuts] The 5MHz Sweet Spot
>>>>
>>>> This all seems to be forgetting that the crystals are usually
operated at
>>>> 3rd or 5th harmonic. The crystal in a 10811A is 10 MHz/3rd overtone.
A
>>>> high quality 5 MHz/5th overtone crystal is really a 1 MHz
fundamental, a
>>>> large piece of quartz. Running at a harmonic greatly reduces the
influence
>>>> of the package.
>>>>
>>>> David
>>>>
>>>>
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