I would expect that in such place, there would be a lot of competent people that could help ?
At HF frequencies you usually try to avoid too high resonance voltages, since in worst case even with 100 W RF power, you could cause flashover in capacitors rated for kilovolts.
The hard thing is doing that at 500 MHz.
One thing that might be interesting to look at is a 1/4 (or 3/4) wavelength long coaxial resonator, which is tuned with a capacitor at the top of the inner conductor and the outer tube.
A commercial RF power amp will generally be intended to drive a 50 ohm load, which is not to say that it is a 50 ohm source.
A Q of 20 or so might be enough. The problem will be to match an available amp to his load, and keep everything cool.
Maybe some RF amplifier company will give him some help. They may have run into problems like this already.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
An _unloaded_ Q of 20 should be easy to achieve, but since there appears to significant losses (water cooling), what is going to be the _loaded_ Q ?
Winfield Hill wrote in news: snipped-for-privacy@drn.newsguy.com:
Warm to the touch? Or... vaporize me!
Then post enough detail about what the researcher is actually trying to do let us make actually helpful suggestions, as opposed to guesses based on what they might be trying to do.
-- Bill Sloman, Sydney
I found a wikipedia link that had them going down to 600MHz. 500MHz ought to be do-able, but probably not off the shelf.
-- Bill Sloman, Sydney
Superconducting cavities have wonderful characteristics for this kind of problem; how about Q of 10^10 at over a gigahertz?
And Jan Panteltje has played with one - albeit a high temperature super-con ductor cooled with liquid nitrogen (which apparently costs about as much pe r litre as milk, though the trucks that deliver it don't deliver every day, so you need a decent-sized thermos flask to hold a couple of days worth).
Whether the MIT experiment would tolerate a liquid nitrogen cooled resonant cavity is an open question.
John Larkin didn't tell us nearly enough about what the experimenter was tr ying to do.
-- Bill Sloman, Sydney
Our physics lab technician liked to quote a student requesting a stopper for his liquid N2 Dewar to stop it boiling away so fast...
Mike.
Sometimes they ice over, which can get interesting.
John
r
Bizarre - the very cold nitrogen gas that boils off is bone-dry. You'd have to do something very silly to get frost building up where it was coming ou t, but the kind of people who might try to stop it boiling off with a stopp er can manage all sorts of tricks.
-- Bill Sloman
I saw a guy kneeling to work on some gear, spilled the dewar of LN2, froze his knee.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
If not vented properly, LN2 gradually turns into liquid oxygen, which could be dangerous.
A slightly leaky stopper isn't a bad idea. It will reduce boiloff rate and reduce ice buildup.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Maybe the best option is to hunt down a big old used UHF TV transmitter from the analog days. If there is still one that hasn't gone into the crusher. Then call the utility so they can come out with a serious crane and install a massive 3-phase transformer. Make sure the bank account is commensurately filled :-)
Most likely the FCC will also want to have a say in this.
-- Regards, Joerg http://www.analogconsultants.com/
On Nov 24, 2019, Joerg wrote (in article ):
If I recall, these UHF TV transmitters used very large tetrode vacuum tubes, not magnetrons or klystrons.
.Joe Gwinn
er
John Larkin wasn't paying attention to his chemistry lectures at Tulane.
Nitrogen-14 turning into oxygen-16 would involve nuclear transformation, wh ich would be difficult, and the creation of an extra proton and an extra ne utron which is even more demanding.
Liquid nitrogen (boiling point at atmospheric pressure 77K) can absorb oxyg en (bp 90.19K)from the air, if stored in an open topped container
A slightly leaky stopper will stop air from getting at the surface of the l iquid nitrogen - the boil-off rate is set by the heat leaking into the cont ainer, and convection at the surface of the liquid nitrogen shouldn't be a major contributor to that. As long as the nitrogen is boiling off fast enou gh to maintain a one-way flow around the leaky stopper, air can't diffuse i n.
There will be cold spots on the surface of the stopper which could build up frost, but the vent holes should stay frost free.
The cold traps on my vacuum line got collars of crumpled paper, which did f rost up over the day, but didn't block the boil-off.
-- Bill Sloman, Sydney
TV sets are rather picky about the purity of the signal they get.
Radar sets, and some scientific experiments, seem to be less picky.
-- Bill Sloman, Sydney
As I said... three days ago... in the first response to John's request. Sigh.
I think he's saying that O2 condenses out of the air. The reverse of differential distillation/sublimation, if you will. I have no idea if that's a thing, but it make some sense.
pper
. ,That's probably what he had in mind, but he didn't express himself clearly.
That's a vice, and deserves to be picked on
e no idea if that's a thing, but it make some sense.
I was warned against it back in the 1960's. Liquid oxygen can be surprising ly reactive - apparently charcoal soaked with liquid oxygen was once used a s low-brisance commercial explosive, and one of the Open Day tricks was soa king cotton wool with liquid oxygen and setting it on fire. It produced a b rilliant flare.
-- Bill Sloman, Sydney
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