Patent GB-1415639-A (GB)
Title: Direction finding apparatus
IPC: G01S5/00
Filed: 1974-05-21
Abstract: 1415639 Radio navigation SERVO CORP OF AMERICA 21 May 1974 [29 May 1973] 22714/74 Heading H4D  An apparatus for providing a directional heading in response to a radio request, comprises processor means to determine the bearing of a radio transmitter making the request and to generate a digitized output signal representing the bearing information, storage mains containing pre-recorded digits in speech form, and associated playback means to produce electrical signals representing those digits. The apparatus further comprises gate means which is controlled by the output signal of the processor means and which is interposed between the playback means and a speech amplifier, to select and pass on particular signals representing the digits corresponding to the bearing information. As described, the bearing of an aircraft 20 with respect to a direction-finding station 10 is determined by sequentially switching the elements of a receiving aerial array 12 and utilizing the frequency of the resulting Doppler effect modulation. A receiver 14, a data processor 16 giving an output in digital form, and a display device 18 are associated with the aerial array. Output from the receiver 14 is also fed to a squelch control 38 and to a record/playback control 50 over respective lines 40, 54. Output from the data processor 16 is also fed over a multi-conductor line 24 to a series of logic gates 22. A mult-track record/ playback device has a drum 26 on which are a number, such as five, of record/playback tracks 46, ten pre-recorded tracks 28 of the spoken digits zero to nine, and a number of prerecorded tracks 59 of additional information, such as station identification particulars. Record/playback heads 48 are associated with the tracks 46, and playback heads 30, 31 with the tracks 28, 29, respectively. Each one of the heads 30 is connected to a respective gate of the series 22. When a pilot requests a bearing his transmission is detected by the squelch circuit 38, output from which starts the drum 26 rotating by activating its motor 36 over a line 39. It also switches to their record mode the heads 48 for the tracks 46 so that the output from the receiver 14 is recorded through a line 54. Meanwhile, the bearing of the aircraft is being determined. The completion of the pilots transmission is sensed by the squelch circuit which then activates the control 50 to switch the heads 48 to their playback mode and initiates the operation of a sequencer 52 through a line 55. The sequencer first causes a playback of the pilots request by sequentially connecting the output of the heads 48 to a read-out amplifier 34 through lines 56, 37. Said amplifier modulates a transmitter 42, which communicates with the aircraft 20 via an aerial 44. The sequencer 52 then causes a read-out of the bearing information, an appropriate gate of the series 22 being opened in each three successive revolutions of the drum 26 in accordance with the output from the data processor 16. The sequencer then causes readout of the tracks 59 and, finally, shut-down over a line 62. A multi-pole electronic switch having, for example, twelve positions may be used as a sequencer, being driven to position one as the squelch circuit is re-set, and being advanced with each successive rotation of the drum 26 by signals over a line 60.