Re: [time-nuts] 10811 foam enclosure
Q) Has anyone experimented with the amount of insulation on a 10811
oscillator?
a) Look inside a double oven 10811 to see one example of what works.
Q) None of the hp/Agilent bench test equipment that uses these
oscillators uses insulation. Perhaps that's a clue.
a) It is not much of a clue, considering that a patent & knowledgeable
time-nuter can get 10 to 100 + better performance out of them.
Look inside a HP Z3801 GPS.
Q) "how far can you go"
a) One way is to monitor the Oven current. If it goes to near zero you went
too far.
I've found a 50% to 75% reduction in heater current from its room
temperature value works.
A separate issue is if you are cooking the electronics outside of the oven.
Q) too much ... can cause over-heating or instability.
a) To see if the oven controller is becoming unstable,
Just monitor the Oven current and plot how it resettles after making small
changes of a couple volts to the oven voltage or change its case
temperature.
Q) What is the preferred orientation of the unit.
The Zero G tilt axes. The position that tilting the unit a slight amount in
any axes causes the freq to shift in the same direction.
comment) What I've found to be very effective is to place a paper towel
around the osc and put it in a plastic baggie to keep it from generating any
air currents on its own.
Then put that inside of an enclosure that does not have holes, and Hold the
enclosure's outside temperature constant.
I find this technique works great for both Tbolts and 10811's. Easy to get
10 - 100 to one improvement with a little care.
IMHO, You do not need, or even want, to raise the case temperature of a
Tbolt anymore than absolutely necessary.
Just need to keep the Tbolts case temperature from changing very fast (or
very far).
1 deg F per hr max works OK for most units, or for the extreme time-nut, go
for 0.1 degC per hr max rate of change.
To do that, I find mass to be more effective than insulation. (you need some
of both)
I've gotten the best results using Lady Heather's temperature controller
with a small fan blowing air indirectly at the Tbolt's case.
ws
Q) None of the hp/Agilent bench test equipment that uses these
oscillators uses insulation. Perhaps that's a clue.
a) It is not much of a clue, considering that a patent & knowledgeable
time-nuter can get 10 to 100 + better performance out of them.
The spec page for the 10811A is here:
http://www.leapsecond.com/museum/10811a/10811a-spec.jpg
To avoid misunderstanding could you clarify which of those
specifications you can get 10 to 100+ better performance?
Look inside a HP Z3801 GPS.
Right, that's why I wrote "bench test equipment". None of the
hp test & measurement products use insulation around the
10811.
The Z3801A is unique; that was a 1st generation telecom unit;
the only piece of hp gear with a custom heat blanket wrapped
around a stock OCXO.
The outer oven was a hack so Z3801A could meet telecom cell
tower cold weather warm-up specs. In other words, the better
performance they were looking for in that case was warm-up
time; not a tempco or frequency stability spec.
The external blanket is reminiscent of the 115 VAC fast warmup
heater in the vintage 00105 brick oscillators (a predecessor of
the 10544 and 10811).
But unlike the 00105 the Z3801A reportedly uses PID control on
the blanket. For that reason I would expect that the outer shell
could improve the tempco of the oscillator, but I haven't seen
data on that. Does anyone have actual measurements? A long
run with, and without, the outer oven circuit connected would
tell the story nicely.
/tvb
At 06:36 PM 1/9/2011, Tom Van Baak wrote...
The outer oven was a hack so Z3801A could meet telecom cell tower cold
weather warm-up specs. In other words, the better performance they
were looking for in that case was warm-up time; not a tempco or
frequency stability spec.
The Nortel GPSR (Z3801A) had a very loose warm up spec, which wouldn't
have required a double oven by itself: "The GPSR will be permitted a 24
hour warm-up/training period in the event of a power loss and the 24
hour holdover requirement shall be met following this training period."
The other basic requirement was "+/-1 us traceable to and synchronous
with Universal Coordinated Time (UTC) with at least one satellite in
view." Again, a double oven wouldn't be required for that - the GPS
receive itself should do better.
OTOH, it had a spec of +/- 7 us for a 24 hour holdover, which required
a double oven.
Hi
The spec they were after was a warmup to "on frequency +/- 1x10^-8" from -40 C sort of thing. I believe the warmup time was under 15 minutes, but I don't know the exact number.
Bob
On Jan 9, 2011, at 8:43 PM, Mike S wrote:
At 06:36 PM 1/9/2011, Tom Van Baak wrote...
The outer oven was a hack so Z3801A could meet telecom cell tower cold weather warm-up specs. In other words, the better performance they were looking for in that case was warm-up time; not a tempco or frequency stability spec.
The Nortel GPSR (Z3801A) had a very loose warm up spec, which wouldn't have required a double oven by itself: "The GPSR will be permitted a 24 hour warm-up/training period in the event of a power loss and the 24 hour holdover requirement shall be met following this training period."
The other basic requirement was "+/-1 us traceable to and synchronous with Universal Coordinated Time (UTC) with at least one satellite in view." Again, a double oven wouldn't be required for that - the GPS receive itself should do better.
OTOH, it had a spec of +/- 7 us for a 24 hour holdover, which required a double oven.
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At 07:59 AM 1/10/2011, Bob Camp wrote...
The spec they were after was a warmup to "on frequency +/- 1x10^-8"
from -40 C sort of thing. I believe the warmup time was under 15
minutes, but I don't know the exact number.
Nope. It was only spec'd for operation from 0-50C. It was required to
achieve satellite lock within 60 minutes of powerup, but only had to
achieve +/- 1 us (PPS) while locked. Freq spec was < 10E-9 one day
average. You don't even need an OCXO to do all of that.
As I already stated, the warmup/training spec allowed 24 hours, after
which it was expected to be able to holdover for 24 hours within 7 us.
This, while experiencing temperature cycles (0-30C, 20-50C). The
successor, the GPSTM, doubled the warmup to 48 hours, but added an
additional temperature range (35-65C) to the holdover requirement.
The double oven was there for holdover stability, not warmup time.
Hi
Obviously none of the -40 stuff made it into the final Z3801 specification.
From the stories I've heard, it was indeed part of the initial developmental
goal. There were several customers beyond Nortel in the running early on.
The whole idea of un-heated (outdoor box) "nano cells" was around a long
time before it became real. Weather the low end was a Nortel need that they
later dropped or from one of the other guys - no clue. Far to many beers
between now and when I heard the story to remember that sort of detail.
I've never seen any frequency vs temperature data on the "double oven"
10811's that shows they are significantly better than a normal part. HP
apparently never published any data. They also never used the approach
again, despite it's being pretty cheap to build (added parts cost). Looking
at the design, it likely isn't a very low gradient device...
Watching a Z380x do it's prediction stuff, aging seems to be the big issue.
Some of my boxes have taken weeks to get to an acceptable (few us) number.
If there's a weakness to the startup under normal conditions, aging /
retrace is the issue.
The heater jacket design is indeed a bit of overkill for the need, but
that's not the first (or last) time HP has done that in a piece of gear.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Mike S
Sent: Monday, January 10, 2011 8:40 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 10811 foam enclosure
At 07:59 AM 1/10/2011, Bob Camp wrote...
The spec they were after was a warmup to "on frequency +/- 1x10^-8"
from -40 C sort of thing. I believe the warmup time was under 15
minutes, but I don't know the exact number.
Nope. It was only spec'd for operation from 0-50C. It was required to
achieve satellite lock within 60 minutes of powerup, but only had to
achieve +/- 1 us (PPS) while locked. Freq spec was < 10E-9 one day
average. You don't even need an OCXO to do all of that.
As I already stated, the warmup/training spec allowed 24 hours, after
which it was expected to be able to holdover for 24 hours within 7 us.
This, while experiencing temperature cycles (0-30C, 20-50C). The
successor, the GPSTM, doubled the warmup to 48 hours, but added an
additional temperature range (35-65C) to the holdover requirement.
The double oven was there for holdover stability, not warmup time.
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Bob Camp wrote:
the story to remember that sort of detail.
I've never seen any frequency vs temperature data on the "double oven"
10811's that shows they are significantly better than a normal part. HP
apparently never published any data. They also never used the approach
again, despite it's being pretty cheap to build (added parts cost).
Looking
at the design, it likely isn't a very low gradient device...
The whole 10811 double oven effort was in the "expediency" category.
It was done by people who knew little about oven design and
didn't have time to learn. Out of curiosity I kept tabs on
the design, and what I saw made me cringe. There was an absurd wrapping
of coax and flex circuits to try to reduce conductive heat leaks. I guess
they blundered their way to some kind of a design that worked good enough
to ship product. It is not much of a proof or disproof of the 10811
double oven concept. As they say, it is what is it.
Rick Karlquist N6RK
It is perhaps wise to remind ourselves at this point that the designers'
approach was "good enough" whereas the typical time-nut's approach is "as
good as it can possibly be."
On Mon, Jan 10, 2011 at 1:58 PM, Rick Karlquist richard@karlquist.comwrote:
Bob Camp wrote:
the story to remember that sort of detail.
I've never seen any frequency vs temperature data on the "double oven"
10811's that shows they are significantly better than a normal part. HP
apparently never published any data. They also never used the approach
again, despite it's being pretty cheap to build (added parts cost).
Looking
at the design, it likely isn't a very low gradient device...
The whole 10811 double oven effort was in the "expediency" category.
It was done by people who knew little about oven design and
didn't have time to learn. Out of curiosity I kept tabs on
the design, and what I saw made me cringe. There was an absurd wrapping
of coax and flex circuits to try to reduce conductive heat leaks. I guess
they blundered their way to some kind of a design that worked good enough
to ship product. It is not much of a proof or disproof of the 10811
double oven concept. As they say, it is what is it.
Rick Karlquist N6RK
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.
Designers want good enough at the lowest cost. This oven design sounds complicated.
-----Original Message-----
From: "William H. Fite" omniryx@gmail.com
Sender: time-nuts-bounces@febo.com
Date: Mon, 10 Jan 2011 14:04:20
To: richard@karlquist.com; Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] 10811 foam enclosure
It is perhaps wise to remind ourselves at this point that the designers'
approach was "good enough" whereas the typical time-nut's approach is "as
good as it can possibly be."
On Mon, Jan 10, 2011 at 1:58 PM, Rick Karlquist richard@karlquist.comwrote:
Bob Camp wrote:
the story to remember that sort of detail.
I've never seen any frequency vs temperature data on the "double oven"
10811's that shows they are significantly better than a normal part. HP
apparently never published any data. They also never used the approach
again, despite it's being pretty cheap to build (added parts cost).
Looking
at the design, it likely isn't a very low gradient device...
The whole 10811 double oven effort was in the "expediency" category.
It was done by people who knew little about oven design and
didn't have time to learn. Out of curiosity I kept tabs on
the design, and what I saw made me cringe. There was an absurd wrapping
of coax and flex circuits to try to reduce conductive heat leaks. I guess
they blundered their way to some kind of a design that worked good enough
to ship product. It is not much of a proof or disproof of the 10811
double oven concept. As they say, it is what is it.
Rick Karlquist N6RK
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.
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and follow the instructions there.