Patent GB-983338-A (GB)
Title: Improvements in or relating to transmission systems for the transmission of pulse signals
IPC: H04B14/02
Filed: 1963-07-16
Abstract: 983,338. Telegraphy; line transmission systems. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. July 16, 1963 [July 19, 1962], No. 28123/63. Headings H4P and H4R. In a pulse transmission system similar to that described in Specification 983,337 the transmitter comprises two main channels, each including a modulator, the modulators being fed with oscillations phase displaced by 90 degrees. The main channels include D.C. suppressors. In addition each main channel has an auxiliary channel which passes only the D.C. component and modulates the component on a carrier having a frequency outside the main channels' bandwidth. The signals from the four channels are transmitted together with a pilot carrier, and the original pulses are reconstituted at the receiver. A transmitter having separate input pulse sources 2, 3, Fig. 1, includes low-pass filters 15, 16, D.C. suppressors 17, 18, and modulators 7, 8 fed from oscillator 6 through phase shifters 9, 10. The auxiliary channels for transmission of the D.C. component include low-pass filters 22, 23, and modulators 24, 25, which are fed by oscillators 26, 27, providing carrier frequencies outside the bandwidth occupied by the main channels. The transmitted signal is thus as represented in Fig. 3, wherein the outer sidebands carry the D.C. components and are distinct from the inner sidebands which carry the main channels' data. A pilot carrier is derived direct from oscillator 6, and is distinct from the sidebands due to the D.C. suppression; it is therefore not influenced by the modulating pulses. At the receiver, Fig. 2, the signals are demodulated at 48, 49 with signals from a local oscillator 52. Fig. 5a shows the signal in the upper part of Fig. 2. Filters 53, 54 suppress any signal components lying outside the information band, and at the outputs of lowpass filters 57, 58 appear voltages dependent on the mutual phase relation of the pilot signal and the outputs of phase shifters 50, 51. The voltages are subtracted at 59 and fed to unit 60 which phse-corrects the local oscillator. The D.C. component of the output of modulator 48 is applied as a level control signal to unit 30. Filters 39, 40 select the outer sidebands, Fig. 3, representing the transmitted D.C. component, and, after demodulation, Fig. 5b, the signals have subtracted from them the D.C. outputs of filters 57, 58, Fig. 5c. The resultant signals are added to the main channel signals at 63, 64, Fig. 5d, and squared to provide the original signals, Fig. 5e. In a second embodiment, Fig. 8 (not shown), the transmitter is fed by only one pulse source. The pulses are converted to two pulse trains which act effectively as the separate pulse sources described above, and which have half the bit-speed of the pulse source. The pulses, Fig. 10a, are converted by feeding them direct to one channel and inverted, Fig. 10d, to another channel, each channel including a differentiator, a limiter and a pulse generator, whereby the half-speed trains, Figs. 10a, 10#, are obtained. In this embodiment the auxiliary channel signals are transmitted by frequency modulation. The single pulse train is reconstituted from the two pulse trains provided by the receiver. Fig. 9 (not shown). A further arrangement. Figs. 12, 13 (not shown), includes gating means fed by a clock generator. The transmitter inputs, e.g. magnetic tape records, are sampled by the gates, the samples triggering bi-stable units to give pulse trains suitable for transmission. The received signals, after demodulation, are similarly sampled.