On 11/30/20 2:20 AM, Gerhard Hoffmann wrote:
Am 30.11.20 um 07:00 schrieb Mark Sims:
I once bought a spool of tungsten-rhenium alloy wire on ebay for dirt
cheap. A few weeks later a guy contacted me and offered a lot of money
for it. Turns out they used it to rebuild TWTs.
1. I used to live in Ulm, Germany, where there was? Thales TWT production.
My neighbor and fellow ham worked there, so I got an invitation for their
family-open-house day. That was most interesting. One division looked so
much like a mechanical craft shop: glass blowing, milling, electrical
discharge machining, welding, all so ...retro. And then, the next room:
An array of the best and newest vector network analyzers, with ladies
moving magnets to collimate the beam and maximizing S21.
But I don't think they can survive the GaN revolution.
Yes - that's a fascinating place. It's been there forever under a
succession of names, but I assume all the same people. It used to be a
cavalry station of some sort 100 years ago, people on top floors, horses
on lower floors, etc.
Making & tuning a TWT is a "art" - there's special sauce in the
cathodes, there's special sauce or knack in the tuning - some people are
good at it, others aren't. All the modeling in the world won't replace
those ladies moving little permanent magnets along the tube body to
focus the beam.
I wouldn't be so sure about the GaN revolution overtaking it. TWTAs are
a pretty simple device, easy to get 50-60 dB of gain in a fairly small,
robust package with incredibly wide bandwidth (octaves in some cases),
and DC to RF conversion efficiency >50%.
As a paper in IEEE Proceedings said (in the 80s) - it's a fully mature
technology, and the only reason you haven't seen a particular power and
frequency combination isn't that it can't be done, it's that nobody has
happened to order one like that before.
2. @ Jim: Is there a canonical way to couple a varactor etc to the
DRO for locking without killing Q or without having any effect?
I have made some experiments with 3D-electromagnetics but did
not get very far. It's not for the casual user.
Not that we found - What we were trying to do is get a DRO that was
tunable over a >50 MHz range (at 8.4 GHz) - we had two varactors -
coarse and fine (respectively tightly and loosely coupled), so we'd put
a voltage on the coarse to get it in the right general place, and use
the fine in the PLL loop to lock it.
https://ipnpr.jpl.nasa.gov/progress_report/42-156/156C.pdf
https://ipnpr.jpl.nasa.gov/progress_report/42-166/166A.pdf
Cook, B., Dennis, M., Kayalar, S., Lux, J., Mysoor, N., "Development of
the Advanced Deep Space Transponder", JPL IPN Progress Report 42-156, 15
Feb 2004
Smith, S. , Mysoor, N., Lux, J., Cook, B., Shah, B., "Frequency Agile
Multi-Channel X-Band Coherent Receiver/Transmitter for the Advanced Deep
Space Transponder", JPL IPN Progress Report 42-166, 15 August 2006
Mechanical vibration is probably not an issue for our electron spin
DRO. :-) It weighs more than 3 Kg, most of it iron to support the
DC field magnets. Looks good. I'd like to get one for the mantlepiece.
Our puck has a borehole for a tiny glass pipe through it to apply
the solution with the free radicals. Q takes a hit but there is
still enough left. We get quite a frequency shift when changing
the uMol concentration. Can't tell numbers.
Cheers, Gerhard
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