[time-nuts] 5MHz x 10MHz

[Bob Camp]

Hi

The whole drop frequency / better Q thing really only applies if you are looking for ADEV with tau's > = 0.1 second.  If you are after phase noise, then there are other things to worry about. 

Bob

On Aug 3, 2013, at 7:52 AM, Didier Juges <shalimr9 at gmail.com> wrote:

> Some instruments (Tek 494 for instance) use a 100 MHz VCXO phase locked to 10 MHz for lower phase noise when multiplied into the microwave bands, demonstrating that there is more than one way to skin a cat.
> 
> Didier KO4BB
> 
> Bob Camp <lists at rtty.us> wrote:
>> Hi
>> 
>> The math is pretty simple:
>> 
>> The Q of quartz goes up as the frequency goes down.
>> 
>> A crystal resonator's performance (Q)  is limited by it's thickness to
>> diameter ratio.
>> 
>> At some point the resonator design impacts the Q of the resonator more
>> than the Q of the raw quartz.
>> 
>> Holders are available that will rationally hold a maximum diameter
>> blank.
>> 
>> It's the intersection of all of the above that implies a best solution.
>> The "sweet spot" is not just quartz, it's the combination of all of the
>> above. 
>> 
>> Change any of the above (like the holder) and you get another "sweet
>> spot"
>> 
>> -------------------------
>> 
>> Is that simple? Of corse not. Many things need to change to let you
>> make a high performance blank that's much bigger. Many things need to
>> change to keep the Q of the quartz the limiting factor. 
>> 
>> -------------------------
>> 
>> Why has it not been done? The drive in the marketplace is to smaller /
>> cheaper. This is totally the opposite direction from that. The
>> investment to make larger blanks goes at least back to the design of
>> the gear that grows quartz. What we have is "good enough", but it's far
>> from the best we could do. Quartz is not the limiting factor.
>> 
>> Bob
>> 
>> 
>> 
>> On Aug 2, 2013, at 7:52 PM, Tom Knox <actast at hotmail.com> wrote:
>> 
>>> 
>>> Interesting, I have heard for years from the senior Time and Freq
>> researchers I work with that 5MHz was a sweet spot. I will ask if there
>> is a reason and proven physics behind it but these are individuals that
>> are well grounded in science.  They almost always multiply 5MHz if they
>> needed 10MHz etc.
>>> Perhaps I missed something. It wouldn't be the first time I was
>> schooled by the TimeNuts. 
>>> Best Wishes;
>>> Thomas Knox
>>> 
>>> 
>>> 
>>>> From: lists at rtty.us
>>>> Date: Fri, 2 Aug 2013 14:39:21 -0400
>>>> To: time-nuts at febo.com
>>>> Subject: Re: [time-nuts] 5MHz x 10MHz
>>>> 
>>>> Hi
>>>> 
>>>> Quartz it's self has no "sweet spot". The only issue is how low you
>> can go in a specific sized crystal holder before you start to run into
>> trouble. A TO-5 crystal will have a different minimum frequency than an
>> HC-40.
>>>> 
>>>> Bob
>>>> 
>>>> On Aug 2, 2013, at 2:30 PM, Mike Feher <mfeher at eozinc.com> wrote:
>>>> 
>>>>> It was my understanding that this "sweet spot" was optimum a little
>> above 3
>>>>> MHz, so, 3rd overtone crystals are used to generate a stable, low
>> phase
>>>>> noise 10 MHz.  Prior to that, 5 MHz was used and before that 1 MHz 
>> 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 Tom Knox
>>>>> Sent: Friday, August 02, 2013 2:02 PM
>>>>> To: Time-Nuts
>>>>> Subject: Re: [time-nuts] 5MHz x 10MHz
>>>>> 
>>>>> It is my understanding that Quartz has a sweet spot at 5MHz that
>> makes it
>>>>> ideal if the lowest possible phase noise and highest stability are
>> needed.
>>>>> 
>>>>> Thomas Knox
>>>>> 
>>>>> 
>>>>>> Date: Fri, 2 Aug 2013 19:57:16 +0200
>>>>>> From: magnus at rubidium.dyndns.org
>>>>>> To: time-nuts at febo.com
>>>>>> Subject: Re: [time-nuts] 5MHz x 10MHz
>>>>>> 
>>>>>> Hi Euclides,
>>>>>> 
>>>>>> On 02/08/13 18:31, Euclides Chuma wrote:
>>>>>>> Hi,
>>>>>>> 
>>>>>>> Why any equipments use 5 MHz and others use 10 MHz reference
>> standard?
>>>>>> 
>>>>>> There are some benefits (traditionally) in using 5 MHz over 10
>> MHz, 
>>>>>> but
>>>>>> 10 MHz have become a common standard. The actual frequency isn't 
>>>>>> really magic, but 5 MHz and multiples became somewhat standard in
>> the 
>>>>>> old MIL STD 188 for time-keeping, and it fit fairly well with what
>> was 
>>>>>> already in use. There are folks here that can correct me on
>> massive
>>>>> details.
>>>>>> 
>>>>>> Today 10 MHz is more common because, well, engineers then to be 
>>>>>> following habits, and 10 MHz "sounds nice". I use 10 MHz mainly 
>>>>>> because the application requires it, otherwise I use whatever 
>>>>>> frequency fits my other needs, or what becomes easy to source.
>>>>>> 
>>>>>> PS. Have not seen you post before, so welcome to time-nuts!
>>>>>> 
>>>>>> Cheers,
>>>>>> Magnus
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