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 <[email protected]> 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 <[email protected]> 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: [email protected] >>> Date: Fri, 2 Aug 2013 14:39:21 -0400 >>> To: [email protected] >>> 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 <[email protected]> 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: [email protected] >[mailto:[email protected]] 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: [email protected] >>>>> To: [email protected] >>>>> 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 >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] To unsubscribe, go to > >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
