Post B4glfggA2apgKRL5QO by dec23k@mastodon.ie
 (DIR) More posts by dec23k@mastodon.ie
 (DIR) Post #B4fIH7RQJJgkGJQ0XY by themaritimegirl@tech.lgbt
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       I've always noticed in vintage news coverage of the Apollo moon landings, you can occasionally hear what sounds like distant MF tones, like those used in the old electromechanical telephone network to connect long distance calls. I've always wondered if that was part of NASA's comms, or telemetry coming from the spacecraft, or what.It turns out the answer is much simpler - comms audio was delivered to media outlets via leased telephone lines, because it was the easiest way to do it, and phone calls were much higher fidelity than they are today. It's just crosstalk between lines, which was common on phone calls.You can hear it clearest at 1:22 and 5:40 in this video. You can even occasionally hear other phone calls, just barely.https://youtu.be/1nVlMg27cik
       
 (DIR) Post #B4fIH7uqXvDxjZBVOy by vwestlife@mastodon.social
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       @themaritimegirl Leased lines typically did not have the same harsh ~3 kHz lowpass filtering as normal telephone lines. You could get a "voice grade" line with about 8 kHz audio bandwidth, or a "dry pair" with no filtering on it at all -- literally just a pair of wires between two locations -- which is what radio stations used for their studio-to-transmitter link (and some still do today!).
       
 (DIR) Post #B4glfggA2apgKRL5QO by dec23k@mastodon.ie
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       @vwestlife @themaritimegirl Or an "unconditioned line" in some countries.You'd have to ask the telco (which was usually the national PTT in most of Europe) for an "alarm circuit", because you were hooking up an old fashioned alarm system.Definitely not doing any data comms. Definitely don't want to buy an overpriced packet switched X.25 line for a point-to-point link. Definitely don't want to sign up for managed services on top of that.