Multitone signalling system employing quenched resonators for use on noisy radio-teleprinter circuits

The paper describes a method of transmitting teleprinter signals over noisy circuits. One tone in the low a.f. range is allocated to each of the 32 characters in the teleprinter alphabet, each tone being transmitted for the duration of the relevant character. At the receiver, the tones are detected by a set of resonators, one of which integrates the entire energy in the transmitted character before it is quenched at the end of the character period. As the tones are orthogonally related, the energy in the resonators corresponding with the unwanted characters is zero at the end of the integration period. Absolute amplitude levels are avoided in the assessing of the integrated energy. The equipment is synchronous, but accepts an input in the form of standard fully perforated tape, and uses a standard start-stop teleprinter for print out. The performance of the system is analysed mathematically, and the results of practical tests are quoted and compared with the published performance of other telegraph systems. It is shown that it is possible to transmit 100 words/min with less than 0.2% errors when the signal is 4dB below the noise level in a bandwidth of 470 c/s. This is an improvement over other known methods, and in particular it is very much better than the performance of a highly skilled Morse operator using a manual system.