[time-nuts] homebrew maser
jfor at quik.com
Tue Aug 31 23:58:41 UTC 2010
Microwave test gear and plumbing is very significantly harder to get at 24
GHz than at 1.4 GHz.
At a guess I've seen easily 100 times more stuff available at 1.4 GHz.
> That's a great article. It almost makes the job seem doable.
> It is going to be expensive, though. If someone can build a working maser
> for less than $10K in materials and bespoke fabrication services alone,
> be impressed. An obvious question is, what's the so-called "minimum
> product" that can actually produce a population inversion in a cavity and
> demonstrate maser action? Do you need any magnetic shielding at all,
> a couple of Helmholtz coils? Maybe not. Do you need to coat the bulb at
> all if you don't care about line width? Maybe not. How exotic does the
> collimator need to be if you don't care much about service life? Probably
> not very. You definitely don't need a multilayer vacuum system. What
> corners can be cut to get a rough prototype running?
> Control electronics is trivial, and not even worth thinking about until
> physical details are nailed down.
> Once you start talking about cutting corners just to get a maser up and
> running, though, there's another obvious question worth considering: what
> about starting with an ammonia maser? This was the first molecular
> oscillator. Experience optimizing the (numerous) operating parameters in
> NH3 maser would no doubt be helpful in later work with an H maser.
> Ammonia molecules have a dipole moment and can be state-selected
> electrostatically. There is no need for either a dissociator or a storage
> bulb, just a basic electrostatic lens and cavity in a vacuum. Townes's
> original 1954 paper makes no mention of magnetic shielding. But at 24 GHz
> high-Q cavity is small and manageable, so if you do have to enclose it in
> mu-metal it's not going to cost a fortune.
> Further, with stabilities in the 1E-12 range, a 5065A-class rubidium
> standard or a well-optimized GPS clock can be used as a reference for
> tweaking and debugging an NH3 maser. If you do manage to build a hydrogen
> maser, OTOH, you are going to need to build at least two of them to get
> idea where your performance floor is.
> Just one possible thought...
> -- john, KE5FX
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>> Behalf Of Bruce Griffiths
>> Sent: Tuesday, August 31, 2010 1:23 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] homebrew maser
>> PTFE wall storage bulb wall coatings haven't been used for some decades,
>> FEP (or the Russian fluoropolymer ) is better in that a smoother coat is
>> achievable see:
>> A sual hexapole state selector is probably a little more effective than
>> the cruder method used in the Russian masers.
>> Mark Sims wrote:
>> > Same general idea, but an image intensifier plate would
>> probably not work well. They are usually thinner and are cut at
>> a bias so the electrons ricochet along its length. You might be
>> able to mount one so that it cancels the bias angle.
>> > They are made by stretching a bundle of hollow glass tubes that
>> have been filled with solid glass rods of a different
>> composition. The original bundle can be very large (like over a
>> meter) and is shrunk down to like 100 fibers per millimeter. It
>> is then sliced and polished. Often the slices (or the pulled
>> bundles) are joined into a bigger plate. Then the inner solid
>> glass is dissolved out with a strong alkali. The hollow tubes are
>> coated with a photoelectric material.
>> > The image from the tube is inverted using a "twister"... a
>> coherent fiber optic rod that has a 180 degree twist.
>> > ---------------
>> > Do you know if the collimator is made from an uncoated
>> microchannel plate?
>> > If so, an old, broken Gen II image intensifier might be a viable
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