[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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