[HN Gopher] Inside a 20-Watt Traveling Wave Tube Amplifier from ...
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Inside a 20-Watt Traveling Wave Tube Amplifier from Apollo
Author : chmaynard
Score : 102 points
Date : 2021-07-08 17:20 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| bluenose69 wrote:
| It would be interesting to learn more about these systems in the
| context of today's systems (say, a cell-phone receiving GPS
| signals), in terms of power received, bandwidth, signal:noise
| ratio, and so forth.
|
| This kind of comparison can be really enlightening, especially to
| younger folks. (I'm not one of those folks ... I find it simply
| amazing how the tiny antenna in my cellphone can receive GPS
| signals at enough power to be useful for decoding position.)
| kens wrote:
| You may know that GPS is built around pseudo-random sequences.
| By correlating the known sequence with what you receive, you
| can extract the signal from a lot of noise. By determining the
| time offset in the correlation you get the distance from the
| satellite.
|
| The interesting thing is that Apollo used a very similar system
| for determining the distance of the spacecraft. They sent a
| pseudorandom signal from the ground and the spacecraft returned
| it. By correlating the sent and received signals, they
| determined the distance of the spacecraft.
| raverbashing wrote:
| > Surprisingly, this amplifier only produced 20 watts of power,
| not much more than a handheld walkie-talkie.
|
| Humm I thought actual radio power of walkie-talkies were in the
| mW range (for regulation and power consumption reasons).
|
| But yes, 20W of radio power is not little (actually it is a lot)
| tyingq wrote:
| Here's a traveling wave tube amp that does 5 kilowatts:
| https://www.arworld.us/post/5700TP12G18.pdf?44385.7040046296
| madengr wrote:
| The tube on the cover of this book is 1 MW at 90 GHz.
|
| https://www.amazon.com/Tube-Guys-Norman-H-Pond/dp/0981692303
|
| It's for an airborne ADS (i.e. pain ray). Good book if you
| want the detailed history of microwave tubes.
| kens wrote:
| Walkie-talkies are mostly .5 to 5 watts, but you can get ones
| with 20 to 40 watts. I'm not sure how legal those are.
| kawfey wrote:
| Whether or not they're legal, they're a bad idea to use next
| to your head.
| Cerium wrote:
| Higher power handheld transceivers usually feature a corded
| microphone to allow increased distance between your head
| and the antenna.
| Stratoscope wrote:
| If you're in the US and have an Amateur license, you can
| generally transmit with up to 1500 watts PEP (Peak Envelope
| Power). Some lower limits apply; for example a Technician
| licensee is limited to 200 watts in the HF bands, but may use
| the full 1500 watts in most VHF/UHF bands.
|
| There is no legal distinction between a handheld and any
| other kind of transmitter. A transmitter is a transmitter.
|
| There is a legal requirement to use the minimum power needed
| to carry out the desired communications, so you should not
| blast out 1500 watts at all times. Especially not next to
| your head!
|
| http://www.arrl.org/frequency-allocations
| kens wrote:
| Author here if anyone has questions on Apollo communication...
| java-man wrote:
| Always enjoy reading your blog. Very informative and
| entertaining. Thank you so much!
| amelius wrote:
| Do you have any I-V plots of the wave tube?
| kens wrote:
| I'm not sure that an I-V plot makes sense for a traveling-
| wave tube. It's not like a regular triode tube where you're
| controlling via a grid. Instead, you put in an RF signal and
| the signal comes out amplified.
| tpmx wrote:
| That epoxy-like plastic the components, posts and wires on the
| boards in https://static.righto.com/images/sband-
| twt/transformers.jpg are covered in - looks like it might be a
| way to perform vibration-proofing? Seems like it would be very
| robust.
|
| Know anything more about this method?
| kens wrote:
| The Juno II rocket launch in 1959 spectacularly failed when
| the rocket did a U-turn after launch. The cause was two
| diodes touching due to vibration. After that, rocket
| components were often potted in plastic to prevent similar
| problems.
|
| Video of launch: https://www.youtube.com/watch?v=885as-
| VE50g&t=1446s Discussion of diodes: https://youtu.be/885as-
| VE50g?t=1688
| tpmx wrote:
| 62 years ago. Just letting that sink in. (Thanks for the
| video links!)
| ngcc_hk wrote:
| How does one knew at that time that is the issue ... must
| be a great detective work!
| dr_dshiv wrote:
| Do you know anything about the heart rate telemetry they did?
|
| I'm blown away by the description of the helix that slowed down
| light by 90% so it could interact with the electron beam. Who
| figured that out? Brilliant.
| jhallenworld wrote:
| "Rudolf Kompfner in 1942 --notably after his public
| announcement in 1946-- when he was secretly working on
| microwave vacuum tubes for the British Admiralty at the
| University of Birmingham during World War II. But the history
| of this device is more complex because the traveling-wave
| tube was, consecutively, discovered thrice independently"
|
| https://hal.archives-ouvertes.fr/hal-01754885/document
| kens wrote:
| The biomedical telemetry was a bit complicated (as was
| everything in Apollo). When astronauts were outside, there
| were 7 channels of analog telemetry transmitted by FM to the
| Lunar Module. The Lunar Module converted these channels to an
| AM signal which was transmitted over VHF to the Command
| Module. The Command Module converted these to PCM data, which
| was then sent to Earth over the unified S-band system.
|
| For details, see "Unified S-Band Telecommunications
| Techniques for Apollo" page 11.
| https://core.ac.uk/reader/80678138
|
| > Who figured that out? [traveling-wave tube amplifier]
|
| It was Andrew Haeff at RCA in 1933:
| https://patents.google.com/patent/US2064469
| [deleted]
| bwooster wrote:
| Love your articles Ken! Interesting content, straightforward
| but not dry writing, helpful diagrams and images and footnotes.
| s800 wrote:
| More generally, curious about what your plans are for a 400Hz
| power supply. There are so many interesting avionics,
| aerospace, etc. equipment which would be interesting to
| experiment with. Short of spinning a generator, have you found
| a VFD or something else OTS that can supply suitable power?
| Tnx!
| kens wrote:
| CuriousMarc got a VFD box that he thinks will power this, as
| well as some gyroscopes. I don't know the particular model.
| jcun4128 wrote:
| It looks so well made, machined block, wow
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(page generated 2021-07-08 23:00 UTC)