[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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