[GreenKeys] FAA Teletypewriter Network 1959

[Jim Haynes]

On Fri, 2 Oct 2020, Harold Hallikainen wrote:

> All those circuit miles are interesting. I wonder if they ran DC loops out
> to the FSS or if they ran modems. Also, they must have had an interesting
> switching system to get data where it was supposed to go.
>
I don't know, but I expect the telcos used different things depending on
their needs.  The classical circuit, such as used along railroads, is a
single loop that loops through all the stations.  When you get away from
railroads the telcos have to simulate that kind of circuit, running DC
loops from the company office to the customer, and DC loops or carrier
channels to make up the entire inter-city system.  So there are
telegraph repeaters in the central offices to make the system work as if
it were a single loop through all the stations.  You can see some of this
stuff in Western Union Technical Review, and in Bell System publications.
Then for connections from the central office to the customer Bell
sometimes used DC loops and sometimes used modems consisting of
individual channels of 43A1 carrier systems.