Patent GB-635976-A (GB)
Title: Improvements in or relating to navigation aiding radio systems
IPC: G01S1/02
Filed: 1946-08-27
Abstract: 635,976. Radio - navigation. SADIRCARPENTIER. Aug. 27, 1946, Nos. 25676, 25677 and 25678. Convention dates Dec. 20, 1943, April 4, 1944, and Nov. 17, 1944. [Class 40 (vii)] The invention relates to a radio beacon of the type comprising two pairs of antennse or two frame aerials arranged with angularly displaced and preferably mutually perpendicular axes and fed by the same radio frequency signal modulated by the same low frequency, the modulation voltages for the two pairs being displaced in phase by a fixed amount, 90 degrees in the preferred case, and also a fifth antenna transmitting the same radio frequency phase shifted by 90 degrees and modulated by the same low frequency. An example of this form of beacon, Fig. 1, comprises a radio frequency oscillator 8 feeding antenna pairs 3, 4 and 5, 6 through modulators 9 and 10 and the fifth central antenna 7 through 90 degrees phase shifter 13 and modulator 14. A low-frequency oscillator 16 feeds modulator 10 directly, modulator 9 through a 90 degree phase shifter 17, and modulator 14 through adjustable phase shifter 18. The antennµ 3, 4, 5 and 6, create a field the modulation phase of which varies with direction and the total resultant modulation from these antennae and antenna 7 is dependent on the phase of the modulation of antenna 7 and is a maximum (or minimum) in a direction dependent on the phase shift introduced at 18. In order to define a beacon axis the phase shifter may be keyed from one value to another, for example in dot-dash sequence, to define an equimodulation intensity line corresponding either to maximum or minimum resultant modulation. Alternatively by continuously varying the phase shifter 18 a rotating axis may be created. According to the invention in a beacon of this type the low-frequency modulating the fifth antenna transmission is derived from a rotatable coil which is arranged in a rotating field created by two mutually perpendicular coils fed respectively by voltages serving to modulate the two pairs of antennse. The two fixed coils may either be fed directly from oscillator 16 and phase shifter 17, (Fig. 2, not shown), or by voltages obtained by detecting the signals actually radiated (Fig. 3, not shown). To correct for the effect of the spacing of the antennµ pairs the rotatable coil may be rotated at a predetermined varying angular velocity, or a correctly profiled condenser driven with the rotating coil included in the feed to correct the phase to produce a constant angular velocity of beacon axis rotation. These arrangements do not correct for errors in magnitude and a correcting phase shifter which includes means for correcting also for this error is described with reference to Figs. 4, 5 and 6 (not shown). The beacon axis may be rotated at a speed of one revolution a minute, the modulation current of the fifth antenna being subject to complementary laying if desired, and a special signal emitted as the axis sweeps through north, the bearing axis being determined by timing the period between the reception of the north signal and the passage of the axis through the receiver. Instead of using complementary keying the rotating coil may be driven at 25 and 50 revolutions per second and pulses radiated each time the axis passes through a given direction such pulse being used for phase marking on the speed of rotation frequency waveform received. For a standard check reading on all receivers one of the fixed coils may be temporarily disconnected and the energization of the pairs of antennµ stopped. Beacon providing a number of fixed axes. Fig. 7 shows a beacon providing three fixed axes defined by different modulation frequencies. The ratio frequency part of the beacon is similar to that of the known system described but three generators 161, 162, 163 of different modulation frequencies are provided feeding modulator 10 directly and modulator 9 through 90 degree phase shifters 171, 172, 173. The complex modulation of the antenna pairs is derived by detection of the outputs of the modulators 9 and 10 and applied to the fixed coils 19 and 20 to provide fields rotating at the different modulation frequencies. In these fields are arranged coils 211, 212, 213 set in accordance with the directions of the desired axes and feeding modulator 14 through tuned filters 221, 222, 223. Because of these filters the effect is the same as if each coil was submitted to a rotating field of its own frequency only and three distinct axes are produced. In another embodiment, Fig. 8 (not shown), the modulation frequencies are emitted successively by using a commutator or electronic distributer arrangement.