Len Cutler was pretty much allowed to do whatever he wanted
on the HP106 and he produced the proverbial doomsday machine.
I think the SR-71 analogy is good here, except that Kelly
Johnson had a lot more support from his management. Len always wanted
to make an optically pumped cesium as his ultimate doomsday
machine, but management never funded it.
He proudly had a 106 on display in his office. I wish I
had asked him how he got such low aging crystals. 10811
crystals never got much lower than about 1 part in 10^-10
per day.
Rick Karlquist N6RK
On 10/2/2014 11:58 AM, Tom Van Baak wrote:
The most extreme example of slow ovenized oscillator warm-up I've seen is the vintage
hp106. These mid-1960's oscillators were designed as the ultimate, "hp way",
pre-atomic, frequency standard -- expected to be powered up, uninterrupted, for years and
decades. So there was no hurry in the (perhaps once-in-a-lifetime) initial warm-up.
Here's a plot/photo of one I recently tested:
http://leapsecond.com/museum/hp106a/
These HP-106 oscillators are among the best I have ever measured: stability and
daily drift rates in the very low -13's. Like the SR-71, these were designed by
gut and slide rule. And yet achieved extreme performance, even by today's
standards.
The amazing thing -- as you know from your enviable career at HP -- is that an
instrument produced in 1964 can still work 50 years later in 2014. No blown
fuses, no electrolytics, no filaments, no f/w upgrades, no Y2K, no decaying
EEPROM, no batteries, not even any IC's. No user s/w, no USB, no drivers, no
OS. Not even an on/off switch! Just a 5-pin 24VDC backup or 2-prong AC cord in
and a pure 5 MHz BNC out, that's all.
How many of the instruments we use today will still work out-of-the-box in 2064?
/tvb
----- Original Message -----
From: "Richard (Rick) Karlquist" <[email protected]>
To: "Discussion of precise time and frequency measurement" <[email protected]>
Cc: <[email protected]>
Sent: Wednesday, October 01, 2014 9:03 PM
Subject: Re: [time-nuts] How long do ovens take to cool to ambient after power
is removed?
On 10/1/2014 1:04 PM, Hal Murray wrote:
[email protected] said:
Anyway, later today (tomorrow ??) I will post a plot of frequency vs time.
The question is though, how long is thing thing likely to take too cool?
I'd expect an exponential decay so you need to specify how close to ambient
you want to get. I'd guess a ballpark of 10x the warm up rate.
You can probably measure it if you have the warmup graph. Turn it off, wait
a while, turn it on, measure the freq, consult warmup graph.
When I was still with Agilent, I did some experiments with unpowered
10811's. Both the oven and oscillator were unpowered and I measured
the temperature by looking at the B mode resonance of the crystal.
I wanted to get rid of any linear frequency drift. As a rough
rule of thumb, 1 hour of cool down is pretty good for most purposes.
For extreme measurements, I would allow 10 hours. This reduced
any exponential tail to below the ability to measure temperature and/or
below the effects of the ambient. I had to put a box over it to
reduce the effects of air currents. If I did not do that, then 1 hour
was all I needed.
Rick Karlquist N6RK
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