Is SC the most stable cut for lowest phase noise?
My only experience with SC-cut crystals is that time base oscillators in later EIP/Phase-Matrix counters with SC-cut crystal oscillators seem to warm-up from a cold start and stabilize more quickly than earlier AT-cut versions. I was surprised to see from Jeff Cartwright's paper that SC-cut crystals operate at higher temperatures. Could this rapid warm up characteristic be attributable to oven design rather than crystal cut?
Bruce
On 6/9/2022 10:03 AM, Bruce Hunter via time-nuts wrote:
My only experience with SC-cut crystals is that time base oscillators in later EIP/Phase-Matrix counters with SC-cut crystal oscillators seem to warm-up from a cold start and stabilize more quickly than earlier AT-cut versions. I was surprised to see from Jeff Cartwright's paper that SC-cut crystals operate at higher temperatures. Could this rapid warm up characteristic be attributable to oven design rather than crystal cut?
Bruce
Absolutely not. It is strictly due to thermal stress compensation.
Rick N6RK
Hi
There happen to be some AT cut based OCXO’s that beat the typical
SC cut on warmup … just saying …. :)
Bob
On Jun 9, 2022, at 9:03 AM, Bruce Hunter via time-nuts time-nuts@lists.febo.com wrote:
My only experience with SC-cut crystals is that time base oscillators in later EIP/Phase-Matrix counters with SC-cut crystal oscillators seem to warm-up from a cold start and stabilize more quickly than earlier AT-cut versions. I was surprised to see from Jeff Cartwright's paper that SC-cut crystals operate at higher temperatures. Could this rapid warm up characteristic be attributable to oven design rather than crystal cut?
Bruce
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On 6/9/22 8:53 PM, Bob kb8tq via time-nuts wrote:
Hi
There happen to be some AT cut based OCXO’s that beat the typical
SC cut on warmup … just saying …. :)
Bob
On the subject of rapid warm up. I suppose if you had a need, one could
dump as much power as you need into the heater. Turn on oscillator,
lights in room dim for a few moments.
But everything is a tradeoff, and I suspect that over time "standard
designs" sort of migrate to particular ratios of things like peak vs
average heater current, etc. Especially in applications driven by
design rules for things like "maximum current per connector pin" or
"component derating" - I suspect that drives things more than the
fundamental physics, in most cases. Why are diodes rated at 1 or 3
Amps? And not 2?
I think there is a severe misunderstanding of this issue.
First of all, "rapid warmup" is a red herring. The real
issue is "rapid frequency stabilization".
The time it takes for the oven to cut back (typically only
a minute or two) is a very minor part of the time budget
to get to frequency stabilization. You could have an AT
cut oscillator that reached "oven warmup" in 1 second, but
then you would have something like a 1 hour wait to get
frequency stability, due to the thermal stresses.
Part of the reason for the misunderstanding is that the
problem I have described is basically orthogonal to the
proverbial time nut with his master OCXO in an underground
bunker running on an uninterruptible power supply, that has been
powered up continuously for umpteen years.
Rick N6RK
On 6/10/2022 6:47 AM, Lux, Jim via time-nuts wrote:
On 6/9/22 8:53 PM, Bob kb8tq via time-nuts wrote:
Hi
There happen to be some AT cut based OCXO’s that beat the typical
SC cut on warmup … just saying …. :)Bob
On the subject of rapid warm up. I suppose if you had a need, one could
dump as much power as you need into the heater. Turn on oscillator,
lights in room dim for a few moments.
But everything is a tradeoff, and I suspect that over time "standard
designs" sort of migrate to particular ratios of things like peak vs
average heater current, etc. Especially in applications driven by
design rules for things like "maximum current per connector pin" or
"component derating" - I suspect that drives things more than the
fundamental physics, in most cases. Why are diodes rated at 1 or 3
Amps? And not 2?
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On Fri, 10 Jun 2022 at 17:39, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:
On the subject of rapid warm up. I suppose if you had a need, one could
dump as much power as you need into the heater. Turn on oscillator,
lights in room dim for a few moments.
Is that not likely to damage a crystal? Different parts of the crystal and
likely to be at significantly different temperatures at the same time,
putting a lot of stress on the crystal due to a thermal gradient. It's
probably a bit academic, as nobody is going to make an oven that heats up
in fractions of a second, but if one did, I suspect it might not do the
crystal a lot of good. This is only an educated guess - I don't have
anything to back it up.
At the other extreme, would there be any advantage in actually heating the
crystal very slowly, over the course of an hour/day/week, so the
temperature gradient across the crystal is very small? Of course, if an
oven took ages to reach the correct temperature, it would be inconvenient
for most applications, but for some applications, the advantages might
outweigh the disadvantages. Of course, if one does this, I suspect one
would have to cool the crystal slowly too to prevent a significant thermal
gradient across the crystal.
I know it's a bit different, but I have a 600 mm f4 Nikon camera lens. I
was told that Nikon cools the front element over a period of 6 months to
reduce stresses in the glass.
Dave
Hi
Well …. folks have made AT based OCXO’s that heat up in “seconds” ( as in under
a minute ). Back in the 1980’s they stabilized to < 1x10^-7 at least as fast as the
then typical SC based OCXO’s did …. ( < 6 minutes ). Collins bought quite a few of
them over the years.
Bob
On Jun 10, 2022, at 1:25 PM, Dr. David Kirkby via time-nuts time-nuts@lists.febo.com wrote:
On Fri, 10 Jun 2022 at 17:39, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:
On the subject of rapid warm up. I suppose if you had a need, one could
dump as much power as you need into the heater. Turn on oscillator,
lights in room dim for a few moments.
Is that not likely to damage a crystal? Different parts of the crystal and
likely to be at significantly different temperatures at the same time,
putting a lot of stress on the crystal due to a thermal gradient. It's
probably a bit academic, as nobody is going to make an oven that heats up
in fractions of a second, but if one did, I suspect it might not do the
crystal a lot of good. This is only an educated guess - I don't have
anything to back it up.
At the other extreme, would there be any advantage in actually heating the
crystal very slowly, over the course of an hour/day/week, so the
temperature gradient across the crystal is very small? Of course, if an
oven took ages to reach the correct temperature, it would be inconvenient
for most applications, but for some applications, the advantages might
outweigh the disadvantages. Of course, if one does this, I suspect one
would have to cool the crystal slowly too to prevent a significant thermal
gradient across the crystal.
I know it's a bit different, but I have a 600 mm f4 Nikon camera lens. I
was told that Nikon cools the front element over a period of 6 months to
reduce stresses in the glass.
Dave
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Hi,
It is in this context one should look at the CSAC, as the low power
consumption can enable it to be powered on much earlier. It's not that
it's performance is stellar, but when you consider power consumption and
what that can enable, it becomes impressive and another approach to
solve things.
Cheers,
Magnus
On 2022-06-11 00:00, Bob kb8tq via time-nuts wrote:
Hi
Well …. folks have made AT based OCXO’s that heat up in “seconds” ( as in under
a minute ). Back in the 1980’s they stabilized to < 1x10^-7 at least as fast as the
then typical SC based OCXO’s did …. ( < 6 minutes ). Collins bought quite a few of
them over the years.
Bob
On Jun 10, 2022, at 1:25 PM, Dr. David Kirkby via time-nuts time-nuts@lists.febo.com wrote:
On Fri, 10 Jun 2022 at 17:39, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:On the subject of rapid warm up. I suppose if you had a need, one could
dump as much power as you need into the heater. Turn on oscillator,
lights in room dim for a few moments.Is that not likely to damage a crystal? Different parts of the crystal and
likely to be at significantly different temperatures at the same time,
putting a lot of stress on the crystal due to a thermal gradient. It's
probably a bit academic, as nobody is going to make an oven that heats up
in fractions of a second, but if one did, I suspect it might not do the
crystal a lot of good. This is only an educated guess - I don't have
anything to back it up.At the other extreme, would there be any advantage in actually heating the
crystal very slowly, over the course of an hour/day/week, so the
temperature gradient across the crystal is very small? Of course, if an
oven took ages to reach the correct temperature, it would be inconvenient
for most applications, but for some applications, the advantages might
outweigh the disadvantages. Of course, if one does this, I suspect one
would have to cool the crystal slowly too to prevent a significant thermal
gradient across the crystal.I know it's a bit different, but I have a 600 mm f4 Nikon camera lens. I
was told that Nikon cools the front element over a period of 6 months to
reduce stresses in the glass.Dave
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On 6/10/22 12:13 PM, Richard (Rick) Karlquist wrote:
I think there is a severe misunderstanding of this issue.
First of all, "rapid warmup" is a red herring. The real
issue is "rapid frequency stabilization".
Indeed. But to a certain extent, that's why oscillators don't have 5
second warm up times - it wouldn't help. So the "few minutes" is a good
compromise between design simplicity and waiting for the internals to
equilibrate.
I suspect that those fancy USOs in vacuum bottles take a long, long time
to come to equilibrium.
And that is one of the claims to fame of the CSAC - from power on to "on
frequency" is quite short.
The time it takes for the oven to cut back (typically only
a minute or two) is a very minor part of the time budget
to get to frequency stabilization. You could have an AT
cut oscillator that reached "oven warmup" in 1 second, but
then you would have something like a 1 hour wait to get
frequency stability, due to the thermal stresses.