News for hackers. Stuff that matters.

A comment on Inside a 20-Watt Traveling Wave Tube Amplifier from Apollo.

Re:Inside a 20-Watt Traveling Wave Tube Amplifier from Apollo by bluenose69 on Thursday July 08, 2021 @02:17PM (#27775840)
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.)

[ Parent | on HN ]
Re:Inside a 20-Watt Traveling Wave Tube Amplifier from Apollo by kens on Thursday July 08, 2021 @02:34PM (#27776054)
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.

[ Parent | on HN ]