Patent GB-671135-A (GB)
Title: Improvements in or relating to transmitter-receiver radio communication systems
Inventor: MILLS JOHN ROBERT
IPC: G01S13/78
Filed: 1949-01-31
Abstract: 671,135. Pulse modulation systems; radiolocation. MINISTER OF SUPPLY. Jan. 27, 1950 [Jan. 31, 1949], No. 2674/49. Classes 40 (v) and 40 (vii). An intelligence transmission system comprises a transmitter station, which may be a radar responder, radiating groups of pulses the spacings between the individual pulses of which are characteristic of the elements of intelligence (e.g. dots and dashes) to be transmitted, and a receiver comprising a plurality of coincidence circuits each of which delivers an output signal only in response to a particular group of pulses corresponding to a particular element, an equal plurality of integrator circuits each associated with the output of a coincidence circuit and operating means to present the appropriate element of intelligence when the integrated output signals reach a predetermined level. In one embodiment, in which the receiver is associated with the interrogator 1 of a radar system and the transmitter comprises a responder beacon 2, pulses radiated from the interrogator at, for example, a p.r.f. of 150 per sec. each initiate the transmission of a group of pulses from the beacon. These groups may be pulse pairs, the spacing between which is different according to whether a dot or a dash is being transmitted. The relative length of the dot and dash transmissions (that is the relative number of pulse groups in each) is the same as in normal signalling. At the receiver 3 a locally generated strobe pulse derived over line 1A each time an interrogation pulse is transmitted is automatically locked to the first response pulse and fed through delay lines in circuits 6 and 7 corresponding to the pulse pair spacings for dots and dashes respectively to open gate circuits so that pulses corresponding to " dot " groups are passed by circuit 6 and pulses corresponding to " dash " groups by circuit 7. These two series of pulses are fed respectively - to integrators 8 and 9. The integrators are arranged to trigger the presentation means 10 even though some pulse groups are lost in transmission and yet not to operate in response to interfering pulses accidentally possessing suitable spacing but not being repeated as are the true signals. They are also arranged to fail to operate when signals are applied to them at less than a certain frequency. The presentation means may comprise a local audiofrequency generator keyed by the integrator outputs to provide dots and dashes in a headphone circuit. The integrator circuits are described with respect to Fig. 2 (not shown). Radiolocation. The interrogator pulses are also fed from unit 1 to range circuit 4 when the time elapsing between their arrival and that of the first response pulse from receiver 3 is determined and used to indicate range, reply pulses other than the first in each pulse group are prevented from having any effect on the range circuits. A p.r.f. considerably less than that required for intelligence transmission is adequate for range determination and the interrogator may be arranged normally to operate at a p.r.f. of 30 per sec. at which frequency range will be shown but the reply pulses will not be frequent enough to operate the integrator circuits. When it is desired to receive communications from the beacon the p.r.f. is increased, this arrangement enables a number of craft to use the beacon at the same time with a minimum of interference one with another. The pulse pairs used for signalling may be followed by a further pulse, after a constant delay characteristic of the beacon, for beacon identification purposes.