GB581576A - Improvements in or relating to radio beacons - Google Patents

Abstract

581,576. Radio direction-finding. BUTEMENT, W. A. S., and BEDFORD, L. H. Jan. 28, 1944, No. 1684. [Class 40 (v)] In a radio-beacon system in which a field of the equi-signal overlapping-beam type is continuously rotated, the alternate switching of the beam is effected at an audio-frequency producing at a receiver a tone signal which disappears when the receiver is on the equisignal line, the disappearance of the tone permitting an indication of the orientation of the equi-signal line at that instant to be received. As shown, the orientation indications are given by modulating the transmission with a speech record 4, driven by the motor 3 in synchronism with the aerial system 2, the record comprising the numbers 0 to 90, 0 to 180, or 0 to 360. To give indications up to 180 degrees the numbers 0 to 90 may be recorded twice in male and female voices. The aerial system comprises two dipoles 5 arranged symmetrically in an angular reflector 6 and connected to the transmitter 1 through a forked coaxial line 7. Each-branch contains a short-circuited stub 8 at a quarter-wave distance from the junction, the stubs containing diodes 9 which are rendered operative alter- - nately by a 1500 c.p.s. supply 11. Gaps 10 in the outer conductors of the stubs permit biassing voltages to be applied to the diodes. Alternatively, the stubs with diodes may be replaced by variable capacities formed by rotating a disc of dielectric material between stationary electrodes, the disc being slotted or carrying conducting segments so that the capacities of the branches are oscillated alternately between maximum and minimum values. Since the second harmonic of the tone signal will not disappear on the equi-signal line, the co-operating receiver should have a cut-off slightly below this second harmonic frequency.