Does anyone have technical information on Bell 401 datasets, such as the
401H and 401L transmitters, and the 401F and 401J receivers? In particular, I'm interested in what frequencies, signal levels, timing, and tolerances were used.The 401 series used multifrequency signaling, with up to three simultaneous tones out of eleven choices in three bands. Since they were for customer use, I assume that they were chosen to not conflict with in-band MF signaling.
Eric