[HN Gopher] Inside a 20-Watt Traveling Wave Tube Amplifier from ... ___________________________________________________________________ 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 ___________________________________________________________________ (page generated 2021-07-08 23:00 UTC)