@gunrunnerjohn posted:Why they didn't just do radio is somewhat of a mystery. I know they say they didn't "own" any frequencies, but I can't imagine that was a major stumbling block for a company the size of PRR to deal with.
I wager maybe the regulations. Seems that there was a lot going on between the 30's and 40's with the agencies that existed at the time. I looked up Train phone and there was a few links off of that talking about what today is the ITU I think it was. They were the result of two agencies joining.
It could also be that they didn't want anyone "spying" on their operations. I would imagine that alone would be a factor into developing something that is your own to ensure their company is secure from outside interference.
I wish I copied some of the Wikipedia stuff, hard to do on my phone.