Patent GB-521233-A (GB)
Title: Control means for radio transmitting system
IPC: G01S1/02
Filed: 1938-12-03
Abstract: 521,233. Directive wireless systems. DUNCAN, W. O. (Intercontinental Service Corporation). Dec. 3, 1938, No. 35262. [Class 40 (v)] A radio transmitter, particularly one of the overlapping-beam type, is supervised by a local receiver which puts the transmitter out of action if the radiated field deviates from predetermined upper and lower limits. Green and red indicator lamps are also energized respectively when (a) the transmitter and control receiver are functioning normally and (b) either the transmitter or the control receiver is not. The overlapping beam transmitter 4 which radiates overlapping fields modulated with different frequencies from the crossed loops 2, 3, is energized from the power lines 14, 15. The pick-up system of the control receiver which comprises the plates or coils 31, 32 coupled to the radiating loops feeds the detector 33 and rectifier 35, the two grids of which are so biassed that for equal inputs unequal plate currents give a resultant current through the relay coils 36, 37. Relay 21 operates at a lower current than relay 22, so that for normal operation of the transmitter 4, when the pickups on the plates 31, 32 are equal, relay 21 is operative and relay 22 is inoperative, the contacts 21a and 22a being then open. Any unbalance in the transmitter 4 varies the current through relay coils 36, 37, causing relay 22 to be operated and relay 21 to be released. This closes contacts 22a or 21a and energizes relay 19, which opens contacts 17, 18 to de-energize the transmitter 4 and the relay 45, thereby extinguishing the green lamp 41 and lighting the red lamp 40. A time-delay relay 25 is included in the common lead of the energizing circuits of relays 19 and 45, so that for a short period after connecting the main power lines 14, 15 to an electrical source, the control system is inoperative and the red lamp 40 is energized. The control system for the landing-beam transmitter 6 operates in a similar manner. If the energy picked up by the aerial 61 of the corresponding control receiver 60 differs from predetermined limits, the relay 52 is operated to de-energize the transmitter 6 and relay 85, which extinguishes the green lamp 81 and energizes the red lamp 80. Manual switches 16, 56, and 72 are also provided for cutting-out the overlapping- beam transmitter, landing-beam transmitters, and control systems as required. When the overlapping-beam transmitter is keyed by complementary signals, the system described is not suitable since the discontinuous signals would continually operate the control relays. In this case (Fig. 2, not shown), the relays 21, 22 are controlled by separate coils energized from storage condensers which are charged through circuits including relays controlled by the rectified pick-ups from the coupling elements 31, 32 ; the transmitter is then only de-energized when the received field strength is below a pre-determined limit. When it is desired to control a double-tone overlapping-beam transmitter by the state of the radiation field at some distance from the transmitter, the control receiving system (Fig. 3, not shown), may comprise a single aerial feeding a receiver which separates the two tone frequencies. These are then rectified and used to control two relays corresponding to the relays 21, 22.