[time-nuts] The 5MHz Sweet Spot

Bob Camp lists at rtty.us
Sun Nov 3 08:09:37 EST 2013


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 at aol.com wrote:

> 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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>>>> 
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