Re: [time-nuts] Bye-Bye Crystals
Hi Bob,
If one prototypes any crystal oscillator, and runs it on a bench. Then
builds an 'oven' of sorts and runs it on the same bench. Would you
expect to see any improvement?
In other words for a given oscillator (crystal and electronics, etc),
will there be any improvements in an oven compared to not in an oven?
Or, are there other things that outweigh the gains by temp controlling
the whole thing.
Yeah, this is a pretty open question, but I don't really have a feel for
how good an oscillator needs to be before an oven starts to improve
things...
Dan
On 3/15/2017 12:00 PM, time-nuts-request@febo.com wrote:
Hi
Where do you plan on getting an OCXO grade crystal at an odd frequency like
that? Much of the performance of a good OCXO is in the crystal. Doing a proper
design on one is a lot of work. You might think that having a design for 5.000000
MHz would give you a good design for 5.000050 MHz. I have empirical evidence that
this isn’t the case. Many years later, I’m still utterly amazed that this is the way things
work in the crystal business ….( = it’s not just a design issue, it’s also a business decision)
More or less the crystal needs to be:
- Cut specifically to have a turn at a temperature that makes sense for your application.
- A “large blank” design (for it’s frequency)
- In a cold weld package (most of the normal crystals are resistance weld)
- Run through a high vacuum / high temperature process
- Be plated with gold rather than something like silver or aluminum (unless it’s at VHF).
- Have a motional capacitance that makes sense for your EFC range ( normally = minimize)
- Preferably be an SC or modified SC cut.
This is for a high stability part. The list does keep going on for a while, but that should
give you a pretty good idea.
Bob
Hi
On Mar 15, 2017, at 3:55 PM, Dan Kemppainen dan@irtelemetrics.com wrote:
Hi Bob,
If one prototypes any crystal oscillator, and runs it on a bench. Then builds an 'oven' of sorts and runs it on the same bench. Would you expect to see any improvement?
Sure, the XO likely moves 50 to 100 ppm over -30 to +70. You will cut that down to a couple of ppm. It’s much easier these
days to just buy (or salvage) a cheap TCXO to get the same level of stability.
One very basic issue: If I just grab a random crystal, it likely is a cut that does not have a useful turn temperature at all. For
a proper OCXO you need a crystal with a turn temperature in the practical range for your oven. There are many other
issues.
The key point (just as in the previous message) is that you must have good frequency vs temperature data to know if
you are improving things or not. That involves having a real temperature test chamber than can be slewed in a controlled
fashion and repeatably set to a sequence of temperatures. A typical run starts at room, steps down to cold (or up to hot).
It then steps to the other end and finally steps back to room. Data is taken every 10C or so and analyzed to be sure that
things are not all messed up. One obvious problem / issue would be drift during the run. A typical run takes several hours to
most of a day.
Bob
In other words for a given oscillator (crystal and electronics, etc), will there be any improvements in an oven compared to not in an oven? Or, are there other things that outweigh the gains by temp controlling the whole thing.
Yeah, this is a pretty open question, but I don't really have a feel for how good an oscillator needs to be before an oven starts to improve things...
Dan
On 3/15/2017 12:00 PM, time-nuts-request@febo.com wrote:
Hi
Where do you plan on getting an OCXO grade crystal at an odd frequency like
that? Much of the performance of a good OCXO is in the crystal. Doing a proper
design on one is a lot of work. You might think that having a design for 5.000000
MHz would give you a good design for 5.000050 MHz. I have empirical evidence that
this isn’t the case. Many years later, I’m still utterly amazed that this is the way things
work in the crystal business ….( = it’s not just a design issue, it’s also a business decision)
More or less the crystal needs to be:
- Cut specifically to have a turn at a temperature that makes sense for your application.
- A “large blank” design (for it’s frequency)
- In a cold weld package (most of the normal crystals are resistance weld)
- Run through a high vacuum / high temperature process
- Be plated with gold rather than something like silver or aluminum (unless it’s at VHF).
- Have a motional capacitance that makes sense for your EFC range ( normally = minimize)
- Preferably be an SC or modified SC cut.
This is for a high stability part. The list does keep going on for a while, but that should
give you a pretty good idea.
Bob
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I would be careful to get an all analog tcxo. The digi-trim ones while may
have a decent total error band over temperature can hop up and down in 100
ppb steps when the temperature straddles two points on its temp comp table.
On Wed, Mar 15, 2017 at 7:06 PM Bob Camp kb8tq@n1k.org wrote:
Hi
On Mar 15, 2017, at 3:55 PM, Dan Kemppainen dan@irtelemetrics.com
wrote:
Hi Bob,
If one prototypes any crystal oscillator, and runs it on a bench. Then
builds an 'oven' of sorts and runs it on the same bench. Would you expect
to see any improvement?
Sure, the XO likely moves 50 to 100 ppm over -30 to +70. You will cut that
down to a couple of ppm. It’s much easier these
days to just buy (or salvage) a cheap TCXO to get the same level of
stability.
One very basic issue: If I just grab a random crystal, it likely is a cut
that does not have a useful turn temperature at all. For
a proper OCXO you need a crystal with a turn temperature in the practical
range for your oven. There are many other
issues.
The key point (just as in the previous message) is that you must have good
frequency vs temperature data to know if
you are improving things or not. That involves having a real temperature
test chamber than can be slewed in a controlled
fashion and repeatably set to a sequence of temperatures. A typical run
starts at room, steps down to cold (or up to hot).
It then steps to the other end and finally steps back to room. Data is
taken every 10C or so and analyzed to be sure that
things are not all messed up. One obvious problem / issue would be drift
during the run. A typical run takes several hours to
most of a day.
Bob
In other words for a given oscillator (crystal and electronics, etc),
will there be any improvements in an oven compared to not in an oven? Or,
are there other things that outweigh the gains by temp controlling the
whole thing.
Yeah, this is a pretty open question, but I don't really have a feel for
how good an oscillator needs to be before an oven starts to improve
things...
Dan
On 3/15/2017 12:00 PM, time-nuts-request@febo.com wrote:
Hi
Where do you plan on getting an OCXO grade crystal at an odd frequency
like
that? Much of the performance of a good OCXO is in the crystal. Doing a
proper
design on one is a lot of work. You might think that having a design
for 5.000000
MHz would give you a good design for 5.000050 MHz. I have empirical
evidence that
this isn’t the case. Many years later, I’m still utterly amazed that
this is the way things
work in the crystal business ….( = it’s not just a design issue, it’s
also a business decision)
More or less the crystal needs to be:
- Cut specifically to have a turn at a temperature that makes sense
for your application.
- A “large blank” design (for it’s frequency)
- In a cold weld package (most of the normal crystals are resistance
weld)
- Run through a high vacuum / high temperature process
- Be plated with gold rather than something like silver or aluminum
(unless it’s at VHF).
- Have a motional capacitance that makes sense for your EFC range (
normally = minimize)
- Preferably be an SC or modified SC cut.
This is for a high stability part. The list does keep going on for a
while, but that should
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.