Patent GB-604203-A (GB)
Title: Improvements in or relating to radio systems for communication with moving vehicles
IPC: G01S13/82
Filed: 1945-04-13
Abstract: 604,203. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd. April 13, 1945, No. 9321. Convention date, April 20, 1944. [Class 40 (v)] A radio communication system for moving vehicles comprises a chain of fixed directional multichannel repeaters between two terminal stations, some of the repeaters also being provided with wide angle transmitters used for communicating with a vehicle moving on the path of the repeaters, from a terminal station. As described, an intercalated pulse - modulated multichannel system is provided, some of the channels of which are reserved for inter-terminal communication, the others being available for communication to or from the moving vehicles via wide angle transmitting and receiving aerials. In one embodiment, Fig. 1, west and east terminals 10, 12 are interconnected by relay towers 13, 14 &c. carrying directional aerials 21, 21a and 22, 22a and wide angle transmitting aerials 23 and receiving aerials 24, for communication with aircraft E, F, G. The narrow beam transmissions are made on successive frequencies F1, F2, F3 in the eastbound direction and westbound frequencies F4, F5, F6. The wide angle transmission from aerials 23 are on the same outgoing frequencies as those from aerials 22a, namely F1, F2, F3, but a frequency F7 received from the aircraft is used by aerials 24. Twelve intercalated pulse channels are provided for, the first six of both the eastbound and the westbound being used for communication between west terminal 10 and aircraft and the remainder for interterminal communication, the first being used as a synchronzing monitoring and order channel. West terminal equipment, Fig. 2. The channel inputs and outputs are connected to a switchboard 30. The outgoing channel signals of frequency F1 radiated from aerial 21a and radio transmitter 54 consist of pulses from modulators 31 ... 37 &c. fed with a base wave from source 40, through individual phase shifters 42 ... 47 in the case of channels other than the first, and producing push-pull time displacement modulation of each pulse pair. A suitable modulator circuit is described, Fig. 6 (not shown) which is of the type described in Specification 600,244. A source 51 of synchronizing signals is connected to the modulator 31 of channel 1 and may provide a distinguishing tone or time displacement. A filter 27 removes the synchronizing frequencies from the intelligence signals applied to the modulator. Incoming westbound signals from aerial 22, detected at 60, produce video pulses which are applied to pulse demodulators 64, 75 &c. of the type described in Specification 600,252 through gating channel selectors 61, 72 &c. supplied with gating pulses from a source 67, through individual delay devices 70. The source 67 in the absence of synchronizing signals produces pulses of a slightly lower frequency than the channel pulse recurrence frequency. The channels are thus selected in rotation in circuit 61 until channel 1a is received. The synchronizing frequency then appears in demodulator 64 and is selected by filter 66 and applied to synchronize the generator 67. Thereafter all the channels are held in synchronism. Repeater equipment, Fig. 3. At the eastbound repeater incoming signals at frequency F1 received on aerial 21 are retransmitted at frequency F2 to the next repeater from aerial 21a and broadcast from wide angle aerial 23 at the same frequency for reception by aircraft such as 82. At the westbound repeater, incoming signals from the adjacent repeater on a frequency FS are received on aerial 22a and pass through detector 150, amplifier 151 and transmitter 152 being retransmitted at frequency F4 from aerial 22. Signals from aircraft 82 are received on non-directional aerial 24 and inserted in signal-free channels in the main system. For this purpose a base wave generator 157 is synchronized by channel 1 in the main system by a unit 62b corresponding to unit 62, Fig. 2, and is used to control pulse generators and modulators 162, 177 &c through individual phase shifters 176. The modulator outputs are combined and applied to transmitter 152 over lead 164. The channels W1 ... W6 from the aircraft are discriminated by their different pulse width, in units 165, 175 &c. whose circuits are described later. Aircraft equipment, Fig. 4. The receiving aerial 84 feeds R.F. detector 85 which can be tuned to the signals radiated from any relay station. Channel 1 is selected by unit 62a, corresponding to unit 62, Fig. 2, which feeds intelligence signals to headphones 88 and gating pulses through delay device 90 to channel selector 92 followed by demodulator 94 of channel 2 and through an adjustable delay device 100 enabling any one of channels 3 to 6 to be selected in selector 102. The selected channel pulses, after demodulation in 104 are fed to headphones 105. For transmission a base wave generator 110 feeds pulse generator modulators 112, 114, 116 the last two through phase shifters 113, 115. The modulator outputs for channels 1a and 2a are passed through shapers 122, 124 to produce pulses of fixed but different widths. The shaper 126 following modulator 116 gives pulses of adjustable width which may correspond to any of the widths set at the repeater station, Fig. 3, to feed to channels 3 to 6. The combined channel outputs are fed over common line 130 to amplifier 127, transmitter 131 and aerial 132. Pulse width discriminator, Fig. 8. A circuit for selecting pulses of one width only to the nearest one hundredth of a microsecond as used in the units 165, 175, Fig. 3, includes an amplitude limiter stage 250 the anode circuit of which comprises a resistance R and shock excitable L-C circuit 263. Circuit 263 is normally damped by the conducting triode 260 connected across it but the voltage across resistance R is applied to its grid so that when a pulse occurs at the anode of valve 250, valve 260 is cut off and circuit 263 can oscillate. If the pulse period is exactly half the natural period of circuit 263, the second shock-excited half wave is reinforced by the trailing edge of the pulse and is of greater amplitude than corresponding half waves produced by incorrect pulse widths. A clipping valve 275 therefore can be set to select only the desired peaks of these half waves corresponding to pulses of the required width which are differentiated and clipped in circuit 280 to produce corresponding sharp output pulses. In a second embodiment of the invention, Figs. 10, 11, 12 (not shown), provision is made for broadcasting only the outbranching channels at the relay station and for inserting inbranching channels on the same channel pulses containing the outbranching channels. The aircraft transmission channels comprise amplitude-modulated carriers of different frequencies separately detected at the relay staions to produce the inbranching channels. In a further embodiment, Figs. 13-17 (not shown), the operator at the west terminal can transmit a selected channel to a selected relay tower for transmission therefrom independent of other relay towers for aircraft reception. This is accomplished by pulse width selection, each tower or a group of towers being receptive to a given pulse width. The aircraft receivers are also provided with pulse width 'discriminators. Specification 600,291 also is referred to.