Patent GB-1258996-A (GB)
IPC: G01S19/48
Filed: 1969-11-13
Abstract: 1,258,996. Radio navigation; aerials. HONEYWELL Inc. 13 Nov., 1969 [13 Nov., 1968], No. 55586/69. Headings H4A and H4D. A signal transmitter having a radiator structure which in operation radiates a signal providing directional guidance along a fixed path line, and a device which, if the radiator structure becomes displaced from a predetermined orientation, results in the radiation by the transmitter of a second different signal instead of the first signal. As described, a fixed station for an aircraft traffic supervisory system includes four directional transmitting aerials 23, 24, 25, 26, Fig. 1, for beams which are, respectively, Up, Down, Left and Right of a boresight, said aerials being mounted on a common structure with which is associated a tilt switch which operates should an inacceptable movement of the aerials occur. In normal circumstances, a signal generator 10 supplies a triggering pulse to a station code and range reply generator 13 which then produces three pulses in a predetermined time sequence on leads 35, 36, 37 to a modulator 14. The generator 10 also supplies a pulse over a lead 40 to a tilt alarm 15, which is passed over a lead 41 to a lobe selector 16. In response to this pulse the selector 16 supplies a signal along one of four leads 44- 47, causing a four-position R.F. switch 21 to connect an input lead 52 to one of the four aerials 23-26. In addition, the selector 16 provides to the modulator 14 a further pulse indicative of the guidance lobe being used. A radio transmitter 17 is modulated by the modulator 14, and its output, consisting of four " bursts of R.F. energy representative of three station code pulses and one guidance pulse, is passed via an R.F. switch 20, the lead 52 and the switch 21 to the selected aerial. The switch 20 has been previously positioned by a signal from the generator 10 applied along leads 30 and 32 through the alarm 15. A signal is now applied by the generator 10 along leads 31 and 33, through the alarm 15, which re-positions the switch 20 so that the transmitter 17 is connected to an omni-directional aerial 22. If a correctly coded interrogation signal is received on an omni-directional aerial 12 it is, after amplification in a receiver 11, applied to trigger the generator 13, which delivers a response or range pulse to the modulator 14, and the transmitter 17 produces a single " burst " of R.F. energy which is radiated from the aerial 22. The next three pulses from the generator 10 cause the remaining three guidance signals to be transmitted, the selector 16 switching through its three remaining positions in sequence. Between transmission of the guidance signals, transmission of range signals takes place, if correctly coded interrogation signals are received. The tilt switch comprises a pendulously mounted contact (65), Fig. 2 (not shown), and a surrounding annular contact (64). Should the contact (65) touch the contact (65) because the directional aerial support structure tilts more than a predetermined amount, the coils (67), (80) of relays (66), (77) are energized, and both relays are held through a front contact of the former until a re-set switch (89) is operated. A change-over contact of the relay (66) disconnects the lead 40, Fig. 1, from the lead 41 and connects it to a delay generator having an output lead 42 to the modulator 14. Two changeover contacts of the relay (77) disconnect .the leads 30, 31 from the leads 32, 33 and connect the latter to a power source which maintains the R.F. switch 20 in the position where the transmitter 17 is connected to the omni-directional aerial 22. Consequently, four " bursts " of energy are radiated every time the signal generator 10 pulses, three pulses indicating the station code and a fourth pulse, which is delayed, indicating a tilt alarm. The mobile station equipment has logic circuits which verify the reception of the fixed station code pulses and which identify and utilize the directional guidance pulses which follow in normal circumstances (Fig. 3, not shown). If there is a tilt alarm, the absence of the directional guidance pulses after the code pulses causes warning flags to appear, but an additional and quicker indication is obtained by utilizing the delayed tilt alarm pulses. In means for this purpose an undelayed input pulse on a lead 151, Fig. 4, is compared for time coincidence in an AND gate 174 with a pulse which has been delayed for a time equal to that between the last of the three code pulses and the tilt alarm pulse. Output from the gate 174 energizes a driver 175, which operates a relay 181 via an amplifier 176. A contact of said relay switches on a warning lamp. Reference is made to Specification 1,199,008.