It wasn't unusual for 2-3 code annunciators to go off at the same time for several minutes. Each one had a slightly different tone (frequency) and of course different call letters. But it could get noisy. The dispatchers and operators talked over the top of them when necessary.
Because the annunciators actually used a motor to turn the code generator, they sometimes started slowly with a low tone (in cold weather), and then sped up and got higher before getting to normal speed when they warmed up.
Thanks to everyone for sharing on this topic. Dispatchers today sit at a computer terminal and handle hundreds of miles by themselves. Fifty years ago, dispatchers and dozens of tower/block operators controlled trains using long distance open telephone lines, train orders, OS reports, annunciators, take siding indicators, and many other devices.
Whenever the dispatcher selected/rang a tower, or turned on/off an annunciator or a take siding signal, they punched a device which put out a coded signal to receivers along the line. In every tower, each time a code was sent you could hear it on the receiver/decoder in the tower but it would only ring if it was the number for your tower.
At Town Line, which was a division point between the Detroit Yard dispatcher and the Jackson East dispatcher, there were decoders for both dispatchers which could make it noisy at times.
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