GB1471349A - System for calling a ground station from an aircraft - Google Patents

Abstract

1471349 Calling ground station from aircraft DE STAAT DER NEDERLANDEN TE DEZEN VERTEGENWOORDIGD DOOR DE DIRECTEUR GENERAAL DER POSTERIJEN TELEGRAFIE EN TELEFONIE 29 Aug 1974 [4 Sept 1973] 37725/74 Heading H4L In a system for calling a ground station from an aircraft, in which the ground station automatically monitors radio calls from aircraft which transmit and receive over one of a predetermined number of high frequency carriers, a tone frequency calling code signal is transmitted from the aircraft over any one carrier, and separate receivers for all the high frequency carriers are provided at the ground station. A decoder is connected to all the receivers to identify a completely and correctly received calling code signal for the ground station over any one carrier. When a calling code is identified the transmission of traffic signals over the carrier is enabled. There are eight tone frequencies available ranging from 660-2340 Hz and by pairing them together, each being transmitted for a 1 sec. period, 56 code signals are available and identify particular required ground stations. These codes are modulated on to one of six allocated carriers in the range 4-22 MHz selected by the aircraft pilot in dependence on distance, season, time of day &c. and the modulation may be ordinary amplitude modulation or SSB. The transmitted signal is received by one of the units 1-12 depending on frequency and form of modulation. The transmitted code is determined in a decoding and switching apparatus 26 and contains two parts (a) in formation identifying the called ground station of (b) the direction of the aircraft from it, the form of modulation and a particular terminal served by the station. A received message passes via remote control apparatus 27, 28 and line 29 to a switching apparatus 30 which routes it to the desired terminal, either via main control or other control stations 31, 32. The apparatus 30 sends a signal via 33, 35, 34 to a switching apparatus 36 and thus to the ground station transmitter 37, to adjust it to the appropriate frequency and modulation ready for the return call. The transmission frequency is determined in accordance with the receiver which received the code. The part of the code concerned with direction is used to set the position of aerial 38. The switching apparatus 36 also controls, through 40, 42, 41 and switch 26, the aerial switches 22-25. These are normally oscillating, but must be stopped at the desired direction and frequency. The full code signal (Fig. 2) incorporates a first part in which two distinct frequencies together identify a particular ground station are thrice repeated and a second part in which four distinct frequencies, identify direction, modulation technique and particular called customer are thrice repeated.