Patent GB-845493-A (GB)
Title: Improvements in combined receiving and transmitting apparatus for receiving and transmitting electro-magnetic signals
IPC: H03L7/081
Filed: 1958-09-02
Abstract: 845,493. Radar. SVENSKA AKTIEBOLAGET GASACCUMULATOR. Sept. 2, 1958 [Sept. 14, 1957], No. 28138/58. Class 40(7). In an interrogator-responder system utilizing a modulated carrier wave for the determination of distance means are provided for automatically correcting phase changes in the modulating signal produced by the apparatus itself. Such correction is effected during intervals, termed "calibrating-intervals," which alternate with "measuring-intervals" during which the apparatus operates for distance measurement in conventional manner. Fig. 2, shows one embodiment in which the apparatus, when operating as a responder, receives signals on a carrier frequency of 3000 mc/s. and retransmits signals on a frequency of 2700 mc/s. The local oscillator 18 associated with the (superheterodyne) receiver 10 is controlled by a square wave signal from a source 22<SP>1</SP> to condition the receiver 10 to receive signals alternately on frequencies of 2700 and 3000 mc/s. During the calibrating-intervals the receiver is conditioned to receive signals on 2700 mc/s. directly from the transmitter 17<SP>1</SP> such signals being supplied to an adjustable phase controlling device 16<SP>1</SP> the output from which is fed to a phase detector 11<SP>1</SP> which receives, as a second input, a sinusoidal signal from a source 13 via an adjustable phase controlling device 12 and switch 22 in the position shown. The output of the phase detector 11<SP>1</SP> is then supplied via a gate 20 (rendered conducting during the calibrating-intervals) to adjust device 16<SP>1</SP> until the zero phase difference exists between the input to 11<SP>1</SP> from 16<SP>1</SP> and that from device 12 (at the point 24). The receiver 10 is now conditioned to receive signals on 3000 mc/s. for the measuring interval such signals being supplied, as before via the device 16<SP>1</SP> to the phase detector 11<SP>1</SP>. During this interval gate 20 is rendered non-conducting and a gate 21 is rendered conducting so that the output of phase dector 11<SP>1</SP> is then supplied to the phase controlling device 12 the delay introduced by which is thereby adjusted until zero phase difference again exists between the signals at point 24 and the input to 11<SP>1</SP> from 16<SP>1</SP>. The phase of the modulating signal from oscillator 13 which is retransmitted by 171 is now the same as that of the received modulating signal and independent of inherent phase delay in the apparatus itself. When the apparatus is employed as an interrogator (i.e. at the measuring position) the phase of the square wave signal controlling the beat oscillator 18 is reversed, the transmitter 17 is conditioned by means of switch 221<SP>1</SP> to operate on 3000 mc/s. and switch 22 is shifted between position 23 (during the calibrating intervals) and positions 23<SP>1</SP> (during the measuring intervals). During the former intervals the device 16<SP>1</SP> is controlled by the phase detector 11<SP>1</SP>, as before, to reduce the inherent delay of the apparatus to zero whilst during the measuring intervals the device 12 is operated to cause the overall delay to be zero. Since the overall signal path now includes the distance to be measured the latter may be determined from the amount of delay which the device 12 introduces. An arrangement similar to the embodiment of Fig. 2 but employing frequency modulation of the transmitter and motor driven goniometer devices for the phase control devices 12 and 16<SP>1</SP> is described in connection with Fig. 3 (not shown). A further arrangement, generally similar to Fig. 2, in which the apparatus is normally in its condition for the measuring interval and is tripped to the condition necessary for the calibrating interval for a predetermined time upon the termination of the signal arriving at the receiver is described in connection with Fig. 4 (not shown).