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 <[email protected]> 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 <[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. _______________________________________________ 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.
