The designers of aqueducts and cathedrals and bridges were called architects. Until a few hundred years ago, 'engineer' meant a builder of engines, i.e. war machines (catapults, arbalests, siege engines).
Until the peace of Westphalia, there wasn't much in the way of literature that can tell us about the state of mathematics in elder times. The recently rediscovered Archimedes codex (palimpsest) has come as somewhat of a revelation in that regard.
Recommendation for reading:
Absolutely. Those were the best methods available at the time, so in order to get anything done, they had to do it that way. There are a few instances in which that's still the case, mostly in complex mixed technology situations like autonomous vehicles and space operations. But pure electronics design isn't generally like that any more.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Science just speeds up the process.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Rb and Cs standards tend to use synchronous detection at a CW frequency lik e 137 Hz that doesn't have any low-order harmonics near multiples of 50 or
60 Hz. It's always bothered me that this process works by steering the sys tem towards the point of *worst* signal-to-noise ratio from the perspective of the phase detector. You'd like to lock to the second harmonic instead, but it doesn't convey the phase information needed for a simple lock-in de tector to work.It would be interesting to build a lock-in loop based on something like a B arker code sequence that's easy to autocorrelate. Whether that would make a difference with a cheap rubidium standard is hard to say...
-- john, KE5FX
John Larkin - 200 BC, "We build stuff that doesn't fall down (even though we don't have math)."
-- Rick
That's a serious problem in optics, if you're surfing on a dark fringe--the SNR goes quadratically to zero there, leading to dead-zone type jitter problems. "Dim-field" measurements, where you servo a bit off the null, are a big improvement.
In this case I think it's okay, because the absorption is relatively weak, so the signal goes only linearly to zero, which is what you actually want. The error is
delta f_rms = noise/slope
which stays bounded.
Any AM on the light source goes away as well.
According to your very spiffy web page, Efratom units have a loop bandwidth someplace around 100 Hz, so their dither must be quite a bit faster than that.
The autocorrelation trick would still be peak-following, though. It's hard to avoid the problem when you're trying to sit right at the RF absorption peak.
It's possible to do it by finite differences instead of differentiating, but it would be much harder to get the RF performance right, I expect.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Yeah, I've never done the optical pumping of the hyperfine line of Rb (6.8.... GHz) but the maximum intensity change is never more than a few percent.
George H.
I would use multiple frequencies and extrapolate to zero, but then I've been called a wanker.
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8 Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48
That's all? :) Jamie
So, don't. Measure its length, then weigh it.
-- umop apisdn
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