travelling wave tube

I have not studied electronics but I have studied the Google IT support course among others so I have some basics of how computers and tech work. This type of documentary series is interesting because it brings history to life, and explains how things work. It is not sensationalist, does not use too much music and more. It just guides you through how technology works.

I was surprised to hear that transmission was as low as 2 watts and as high as just 11 watts. I also learned that for some communications they used just two watts of power for Apollo 13, 57 hours into the mission, to reduce power consumption. Of course on Earth they had a 270ft antenna to receive the signal. Compare this to a radio station that may use 50,000 watts. I don’t remember how many watts were used in satellite broadcasting but from a quick skim it’s about 20 watts but this goes to smaller and smaller dishes on earth. Starlink uses about 2 watts of power.

I frequently heard about travelling wave tubes over the years, but I didn’t understand how they work, until this video. I still don’t understand how they work. If my understanding is correct the cathode emits electrons at 20 percent of the speed of light. An RF signal is sent into the tube but has to travel a far greater distance. This slows it down enough for the electrons and the RF signal to synchronise, and the result to be used to transmit. I still don’t understand how it works but I have a starting point. More info can be found here.

There are at least twelve episodes, so if you watch all of them you will get a better understanding of how the comms systems worked during the Apollo space missions. This content is for geeks, who have a basic understanding of at least some of the key topics.

Although this content doesn’t count as archeology in the conventional sense I have put it in that category because it is the study of modern history. People are looking at, and trying to understand objects from a different time. It is within living memory. Living memory doesn’t exclude it from being archeology.