Bob somewhere buried in my collection of interesting bits I have a rather
battered demo sample of what the British GPO Research crystal labs refered
to as an Essen Ring. It is indeed around 3 inches in outer diameter and
almost an inch thick and wide. this would have been cut from natural quartz.
I suspect this specimen is a 'failed' sample. The ring is suspended in a
couple of silk threads.I also have what I think is a higher frequency ring
which is mouned in a 1.5inch diameter evacuated glass holder.
I was told that if the large ring was tapped gently with a pencil it would
'ring' for 5 minutes (that there may be some exageration there) I believe
Qs of 5E^6 were mentioned. More reliable info would be found in the reports
:-)) This was around 60 years ago.
Alan
G3NYK
----- Original Message -----
From: "Bob kb8tq" <kb...@n1k.org>
To: "Discussion of precise time and frequency measurement"
<time-nuts@lists.febo.com>
Sent: Monday, April 05, 2021 9:43 PM
Subject: [time-nuts] Re: Crystal sweet-spot (was: Best frequency to start
for GHz synth ?)
Hi
Back it the “old days” ( so 1960’s in this case ) glass packages
were very commonly used for precision crystals. They were available
in large diameters ( think of transmitting sized vacuum tubes). This
allowed
use of larger diameter blanks than what fit in today’s much smaller
packages.
The result was that things like 2.5 MHz fifth overtone parts could be
made.
Cute things like silk thread supports for the blank were not uncommon.
Yields
simply due to the “thread tweaking” process often ran in the 10 to 15%
range
(as in 8 or 9 out of ten failed …) .
Since there was no way to re-do the process once the part was under
vacuum ( and no way to test it before that) this was indeed black magic.
Occasionally somebody would do a batch and 25% would work. They
would then talk about that event for at least the next 20 years ….
One would *not* want to go back and do it the “good old way”.
Bob
On Apr 5, 2021, at 4:02 PM, Attila Kinali <att...@kinali.ch> wrote:
On Wed, 31 Mar 2021 16:44:40 +0000
"Poul-Henning Kamp" <p...@phk.freebsd.dk> wrote:
It used to be that 5MHz was the "hot spot" for crystals on the
parameters we care about as time-nuts.
Depends on what kind of time-nut you are ;-)
If you are going for high frequencies beyond 1GHz, then a mesa
type high frequency BAW is the best you can do (given you don't
want to use frequency comb to divide down a cryogenic silicon
cavity).
As Bob wrote, for low-frequency, high stability applications,
the lower the frequency of the crystal the better. Or rather,
the thicker the crystal the better. I.e. you want to use an
as low frequency crystal with an as high as possible overtone.
Unfortunately, to make full use of the properties of low
frequency crystals, you need to scale the diameter with the
frequency. Otherwise, the energy loss due to the edges of the
crytal will limit the Q.
For historical reasons, 3rd overtone 5MHz turned out to be the
lowest that could be done economically with the avaible tools
and methods and still fit the size constraints.
Today we could probaly go lower, but the market demands for
large crystal units is shrinking steadily and, as Bob wrote
a few times in the past, nobody has the tooling to do so.
Attila Kinali
--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always
wonder about. And that's why we do research.
-- Kobayashi Makoto
_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
an email to time-nuts-le...@lists.febo.com
To unsubscribe, go to and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
an email to time-nuts-le...@lists.febo.com
To unsubscribe, go to and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an
email to time-nuts-le...@lists.febo.com
To unsubscribe, go to and follow the instructions there.
