Hi Tom I seem to remember seeing a 5MHz standard in a triple oven at PO Research in London were I worked in 1961. The crystal was made there and was a 5MHz 3rd overtone and either a plano-convex or double-convex shape, I believe. They had a lens grinding machine for generating the blanks. This was in the days of the use of natural quartz too.
Alan G3NYK ----- Original Message ----- From: "Tom Van Baak" <t...@leapsecond.com> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Tuesday, January 31, 2012 5:41 AM Subject: Re: [time-nuts] Racal-Dana 1991 w. Option 4C - what is that ? > > What makes 5 MHz more stable than 10 MHz? > > > > Why not 2.5 MHz and double twice? Or 1.25 MHz and three doublers? > > Apparently 2.5 MHz is the most stable of all for reasons not > fully understood, but accepted. That's why the early Sulzer > oscillators were 2.5 Mc. They doubled them to get 5 MHz. > > I don't have a reference handy but there are charts and > curves in old papers on quartz technology that show a peak > in performance (Q?) around 2.5 MHz. Doubling, tripling, or > quadupling works too but you get noise at every stage so > this is not always a solution. > > The 2.5 MHz blanks are very large and expensive; I heard > that's why the industry moved to 5 and then 10 MHz crystals. > Perhaps one of the xtal experts on the list can clarify this for us. > > See also: > > Brief History of the Development of Ultra-Precise Oscillators > http://www.ieee-uffc.org/main/history.asp?file=norton > > Fifty Years of Progress in Quartz Crystal Frequency Standards > http://www.ieee-uffc.org/main/history.asp?file=frerking > > /tvb > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.