[time-nuts] Racal-Dana 1991 w. Option 4C - what is that ?
alan.melia at btinternet.com
Tue Jan 31 06:41:27 EST 2012
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.
----- Original Message -----
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts at 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
> Fifty Years of Progress in Quartz Crystal Frequency Standards
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