GB695353A - Improvements in or relating to radio signalling systems - Google Patents

Abstract

695,353. Automatic phase control systems. POSTMASTER GENERAL. Dec. 1, 1950 [June 13, 1949]. No. 15723/49. Class 38 (iv). [Also in Group XL (c)] A received signal bandwidth is divided into a plurality of sub-channels by filters 12 and a further filter 15 of each sub-channel selects a pilot signal concurrently and separately transmitted in each sub-channel and uses it retroactively to effect automatic gain or both gain and phase control of the signals in each subchannel so that amplitude or both amplitude and phase distortion due to multi-path delay effects in reception from the ionosphere is compensated in the combined output. The system permits increased signalling speed when applied to a high-speed telegraph signal of bandwidth 1000 c/s. divided into ten channels of 100 c/s. bandwidth. The pilot signals are separately transmitted in and may correspond to the mid-frequencies of the sub-channels. The pilot frequencies may be amplified and applied, together with a local oscillator frequency in each sub-channel tuned to a harmonic of the pilot frequency, to a phase discriminator 18, the D.C. output of which maintains the phase of the pilot frequency in the sub-channel constant, and the pilot frequency amplified at 16 and rectified at 17 also applies A.G.C. to each sub-channel amplifier 14. In the combined output of the sub-channels the amplitude/ frequency ratio is constant and the phase/ frequency relation linear. The system may be applied to radio frequencies, amplitude, frequency or pulse modulated, or to the received frequencies of a single side-band receiver after transposing them to an audio-frequency range.