GB848150A - Navigation system with beacon identification - Google Patents

Abstract

848,150. Radio navigation. STANDARD TELEPHONES & CABLES Ltd. June 20, 1958 [June 25, 1957], No. 19825/58. Class 40(7). The invention relates to radio navigational systems in which a beacon station comprises can antenna system for producing a rotating asymmetrical radiation pattern and means for transmitting reference pulse signals when the pattern is in a predetermined position. A particular example of such a system is that known as TACAN. According to the invention the beacon also transmits identification pulse signals which have a repetition frequency which is harmonically related to the repetition frequency of the reference signals and, in order to prevent distortion of the audio tone derived from the identification signals at a co-operating receiver, the reference signals and identification signals are locked in phase. In one embodiment a TACAN beacon 1 and aerial system 2 produce a rotating nine lobed radiation pattern having one of its nine lobes larger than the rest. When the larger lobe passes through the reference direction a pulse forming arrangement 28 triggers pulse generator 22 which emits a characteristic reference signal. The passage of the other lobes through the reference direction similarly coincide with an output pulse from arrangement 26 which triggers pulse generator 23 to produce a second form of reference signal. At the receiver 31 comparison of the amplitude variation of the received signal with the times of arrival of the reference signals and second reference signals give coarse and fine bearing indications respectively. Range information may be obtained by transmitting pulses from the receiver location to interrogate a responder at the beacon. The speed of rotation of the aerial pattern in this embodiment is such that the reference signals produced in generator A are repeated at the rate of 135 cycles a second. The identification signal frequency is made 1350 c/sec. and is produced in oscillator 11 the output of which is modulated by mechanical keying device 18 to give a code signal identifying the beacon. The modulated signal is fed to multivibrator 12 to produce output pulses which are coded and transmitted in the same way as the reference signals. At the receiver the detected pulse signals are passed through a pulse amplifier and clipper 38 to ringing circuit 39 which regenerates the 1350 c/s. modulated audio signal. Two ways of synchronizing the phases of the identification and reference signals are described. In the first of these (Fig. 4, not shown) the output of pulse forming arrangement 26 is fed to synchronize oscillator 11 at a frequency exactly the tenth harmonic of the second reference frequency. In the second (Fig. 5, not shown), the output of oscillator 11 is fed to a count down 10: 1 phantastron frequency divider which provides one input to a phase discriminator. The second input for the discriminator comes from arrangement 26 and the discriminator output is used to control the drive motor 29 of the rotating aerial system so as to ensure the required phase relationship.