Patent GB-717721-A (GB)
Title: Improvements in and relating to radio-location
Inventor: KOTT LEONARD GEORGE WALTER
IPC: G01S3/18
Filed: 1952-05-08
Abstract: 717,721. Radio signalling; radiolocation. ULTRA ELECTRIC, Ltd. Feb. 6, 1953 [May 8, 1952; Oct. 14, 1952; Nov. 14, 1952; 'Nov. 14, 1952], Nos. 11697/52, 25698/52, 28809/52 and 28810/52. Classes 40 (5) and 40 (7) A radiolocation system comprises a beacon transmitter, characteristically pulsed and attachable to flotation equipment worn by a person to be located, and a receiver carried by a search vehicle and using a C.R.T: display by which the pulsed signal can be identified. Means may be provided whereby the transmitter may be keyed for morse code signalling and may alternatively act as a telephony transmitter and receiver, while the search receiver may have direction-finding and distance-determining attachments. In the embodiment described, the beacon equipment comprises a radio-frequency oscillator unit with collapsable aerial which is released, with a main switch, by a lanyard. A second unit comprises a coding circuit or a circuit for telephony and coding while a third unit contains batteries or a battery and vibrator power supply, the three units being in waterproof containers connected by flexible cables, Fig. 1 (not shown). The oscillator unit comprises a valve V1, Fig. 2, arranged to squeg at a recurrence frequency determined by the resistance R1 and condenser C1 in the coding unit, the two units being connected through points A ... E. In order that the signal may consist of groups of a predetermined number of pulses, from two to six, spaced apart by relatively long intervals, a ringing circuit L2, R2, C2 is provided in series with condenser C1. Morse code may be transmitted by 'providing a key which changes the value of resistance R2 to change the number of pulses in a group, such change being visible on the search receiver screen. For telephony transmission and reception a unit comprising a switch 8A ... 8D, Fig. 3, an amplifying valve V2 and a transducer 9, as well.as the coding elements R3, C3, L4, R4, C4, is substituted for the simple coding unit. The switch is biased to be normally in position B, at which coded pulse groups are transmitted. In the T position of the switch, speech voltages from element 9, used as a microphone, are amplified in valve V2 and fed over lead E to the grid of valve V1 to modulate the squegging frequency which is normally set at about 12 Kc/s by resistance R5 and condenser C5. In the R position, speech voltages at the anode of valve V1 are fed through point D to the grid of valve V2 which supplies element 9, acting as a reproducer, with the amplified output. The search equipment comprises the radio receiver a, Fig. 6, feeding the X-deflection plates of a cathode ray tube d-and a triggering circuit b controlling a time-base circuit c feeding the Y-plates of the tube. The time base is triggered by the first pulse of a group, the pulses being displayed as horizontal deflections on one side of the vertical trace. An indication of beacon direction may be provided by connecting the receiver alternately to two differently directional aerials e1, e2 by a switch f1 which is ganged to a switch f2 which synchronously connects the receiver output from one side of the C.R.T. trace to the other.' In order to ascertain the beacon distance an auxiliary transmitter g is arranged to emit a pulse at a controllable time after the arrival of the first pulse of a received group, so that the beacon is triggered thereby to produce the second pulse of its group early. Observation of this pulse on the C.R.T. screen and adjustment of the auxiliary transmitter control to cause its occurrence after a known time interval enables the distance to be determined. Specification 692,987 is referred to.