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Very interesting map. I've always thought of the TV and telephone networks as separate up until the time of the Internet. So, if the map represents Ma Bell, then of course they ran their telephone traffic over these microwave routes. But who's TV signals were being routed over the microwave routes? Was the TV portion of the microwave routes rented mostly to the public broadcast stations? (ABC/NBC/CBS/etc) ??



TV, data and telephone were often carried on the same pipe. Both the coaxial and microwave relay systems were, at their lowest level, broadband analog repeaters that just repeated whatever was sent. A repeater might take everything received between 4320 and 4340 MHz and broadcast the full 20 MHz channel on 4350 to 4370 MHz. If you sent 20 MHz of bandwidth carrying multiplexed voice channels, it would rebroadcast that to the next relay. Same with 20 MHz subchannelized to carry voice channels and two TV channels. Same with some weird digital modulation.

It was fairly agnostic to the actual contents of the channel as long as it fit within the assigned bandwidth. For example, they started using broadband digital modems to carry PCM audio by the 1970s, in parallel to the TV and FM voice. The circuit and packet-switched computer networks AT&T later provided were first carried this way too, as I understand it.

In practice, NBC/ABC/CBS were the biggest clients and used it to relay live network programming, etc. until satellites started displacing that in the 1970s. But it got used for all sorts of esoteric purposes too. Anything you needed bandwidth for, if you could afford it.




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