[time-nuts] 5MHz x 10MHz

[Didier Juges]

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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