Patent GB-615506-A (GB)
Title: Improvements in or relating to wireless signalling apparatus
IPC: G01S1/24
Filed: 1945-03-15
Abstract: 615,506. Radio-navigation. DIPPY, R. J. March 15, 1945, No. 7346/48. Divided out of 615,416. [Class 40 (vii)] A mobile craft receiver for use with a radionavigation system of the type described in Specifications 581,602 and 581,603 or with the system similar in principle thereto described in Specification 615,416, comprises a radio receiver and means whereby the received pulse signals from a selected satellite transmitter may be applied to a centre-zero meter first to cause an indication in one sense and immediately afterwards to cause an indication in the opposite sense, the instant of change-over being controlled by calibrated adjustable timing means to occur at a chosen delay time after the reception of each signal pulse from the main transmitter so that pulses from the satellite transmitter arriving in synchronism with the change-over produce a null indication and signals arriving before or after the change-over result in indications of opposite sense. Adjustment of the timing means to produce a null indication gives a reading of the delay time between the main and satellite transmitter pulses determining the hyperbolic equi-phasal contour line on which the craft is situated. Conversely, by adjusting the timing means to a chosen value and navigating to maintain a null indication in the manner of a left-right indicator enables the craft to be flown along the corresponding contour line; this is of particular value with reference to the system of Specification 615,416, in which the contour lines are substantially straight. The antenna. 40 may feed a receiver 41 whose output is supplied to a selector unit 42 adjustable to be responsive to, and capable of locking itself to, one of a number of different pulse recurrence frequencies, such as are used by the different beacons in the system of Specification 615,416. Unit 42 provides a pulse output coincident with the reception of the pulses of the selected beacon's main transmitter, this is applied to calibrated variable delay means 43 controlling double gate circuit 44 to which the receiver output is also applied. Signals are conducted through the gate for a short period, first over one path and then for a short period over a second path, the change-over time being controlled by the pulse from unit 43. The outputs of the gate circuit may be applied through reversing switch 46 directly and in opposition to a centre zero meter so that signals from a satellite transmitter arriving when the gate circuit is conductive control the meter indication. To provide an aural indication of the A-N type interlocking A-N signals from sources 48a and 48b may be controlled in circuits 47a and 47b by the respective outputs of the gate circuit through the reversing switch 46 so that the amplitude of the A and N signals heard in the phones 49 varies in known manner. Such an arrangement is of particular value when flying along a contour line as in the system of Specification 615,416. The reversing switch enables appropriate left and right indications whatever the quadrant and direction of motion. If a speech communication channel is provided by modulating the pulse width of the main transmitter an additional single gate circuit in the receiver is required to separate out, the main pulses of the required pulse recurrence frequency and apply them to an integrating and filtering unit feeding headphones, Fig. 2 (not shown).