[time-nuts] 5MHz x 10MHz
lists at rtty.us
Mon Aug 5 06:40:09 EDT 2013
Comparing A to B is never easy. There is a wide variation between synthetic quartz processes. The issue with quartz is not so much purity. Synthetic is many orders of magnitude cleaner than natural. The issue is growth rate. Natural quartz grew over centuries, synthetic grows in days / weeks / months (depending). You can indeed get enough goop in the quartz to degrade it, but that's sorted out before you decide to use it for a resonator.
Another issue with synthetic is the seed. You need a seed that's as large (in 2 axis) as the finished bar. The first bar, must come from natural quartz. You can use synthetic seeds for X generations, before you need to go back to natural.
When the switch over was taking place, the common wisdom was that natural quartz was more stable than synthetic. The comparison was begin made to "early" synthetic, so it may not apply to modern material. My guess is that natural quartz is no worse than synthetic for aging.
On Aug 4, 2013, at 9:53 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> wa1zms at att.net said:
>> In a talking to Charles Wenzel about this very topic some 13 yrs ago, I
>> liked it when he said sometimes it comes down to the "quartz-to-crud ratio"
>> of the crystal that makes all the difference for a given crystal frequency.
> Neat. Thanks.
> How much crud is in a typical modern crystal?
> How much was in natural quartz, say from WW II era?
> I assume modern crystals are made from quartz grown in a lab using techniques similar to what the semiconductor industry uses. Are we talking ppm or ppb?
> Does anybody have any long term stability data on old crystals vs modern crystals? Yes, that's not very specific. By old, I'm remembering the crystals I saw as a kid (late 1950s). It was just a few screws to open the package. I expect the ARRL handbook had recipes for adjusting the frequency but my copy from those days is long gone.
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