DIY FAX
Another item from the same 4/34 issue of Radio Retailing.

Several newspapers and radio stations were trying out facsimile broadcasts in the 30s. This article is unusual because the broadcaster was openly inviting DIY experimenters to build their own receivers.



Proprietary systems were the norm then, and still the norm now. From Bell to Edison to RCA to Apple, the manufacturer has always wanted to own the entire system. Content, transmitter, carrier, receiver. You just rent the service.

Walter Damm, interviewed here, took the opposite approach. He told experimenters HOW to build a receiver and invited them to do it.

He doesn't say explicitly, but the system would need a sync pulse to start each scan, and a binary on/off for the pen-down condition. I'm guessing the system used different audio tones for those two types of pulse, sort of like FSK. So you'd need two audio resonators followed by rectification and filtering. You could tune them easily by receiving and listening.

Start with a typewriter. Mount a Strowger relay with a reduction gear driving the platen-turning knob. Use a long-stroke solenoid to pull the carriage rightward quickly. Each time the sync pulse comes through, trigger the solenoid and the Strowger to do a full carriage return operation.** For the horizontal scan, just ramp down the current to the long-stroke solenoid.

For the pen-down signal, another solenoid mounted on the static part of the typewriter, pulling the pen down when the signal is on; or a speaker with a stylus as Damm suggested.

** Later thought: If you had a fully electric typewriter, you could just pulse the carriage return switch, and pulse the period key to make the dots. But the first fully electric typewriter was introduced in 1935. The power-assist type was fairly common, but it wouldn't help in this case.
  ¶ 5:37 PM