[GreenKeys] What is a polar relay for?

[amourdutigre]

Hi,

I have a question that I really cannot find an answer for.

In my readings about electromechanical TTY units, I keep seeing something called a polar relay being referred to. I googled this, and found that it is a device that can be used to revers the polarity on a landline telegraph circuit (not the local loop). Also, most of what little I could find had to do with hand (Morse) telegraphy, nothing with TTY.

I have even seen polar relays referred to in amateur RTTY material from the fifties and sixties.

What were these used for? I found one (I guess, the seller called it a "rolar relay, I suspect a mistype) on e-pay for well over a hundred bucks.

Thank you in advance,

Best and 73,

Joe KB0TXC
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