GB587447A - Improvements in or relating to the superposition of signals on electrical communication systems - Google Patents

Abstract

587,447. Transmitting music &c. RANTZEN, H. B. June 24, 1943, No. 10244. [Class 40 (iv)] A narrow frequency band is removed from a wide-band main signal (e.g. speech or music), and an auxiliary signal is conveyed by a tone within said narrow band, the tone being broken up into Morse or like elements and kept at a relatively low volume, so that it is practically inaudible when the combined signals are converted into sound, but can be isolated by a selective amplifier to yield the auxiliary signal. The main signal may comprise a broadcast programme, and the auxiliary signal used to identify the various items thereof. As shown, a microphone M originates a main signal, covering the frequency range between 50 and 7000 cycles per second, a filter F removes the narrow band 55-65 cycles, and the remaining signal passes to an amplifier A, where it is mixed with a low-amplitude 60 cycle tone from an oscillator O broken up by a Morse key K. The combined signal passes via line L to a broadcast transmitter, speaker or recorder BT. The line is also connected to a selective amplifier SA tuned to accept 55-65 cycles, and yielding the auxiliary signal in the form of a Morse-interrupted 60 cycle tone. The auxiliary signal may be conveyed as a high-frequency tone of say, 4500 cycles, or a combination of tones may be used. Instead of interrupting the tone, the Morse signal may give a slight frequency shift. The amplitude of the tone signal may be automatically regulated according to the frequency gamut of the main signal, or according to distortion conditions.