Patent GB-584727-A (GB)
Title: Improvements in radio control systems for movable objects
IPC: G01S1/30
Filed: 1941-06-04
Abstract: 584,727. Directive radio signalling; thermionic valve circuits. SCHWARZ, H. F., O'BRIEN, W. J., and DECCA RADIO & TELEVISION, Ltd. June 4, 1941, No. 7092. [Class 40 (v)] [Also in Group XXXVI] If two or more transmitters spaced, say, a wavelength apart are energized in phase or outof-phase by currents of the same frequency (or of frequencies, one of which is a multiple of the other), a series of curves may be drawn, each of which is a locus of all points at which the phase relation between the signals from the transmitters is constant. For example, with two aerials A, B spaced a wavelength apart and energized in phase, the series of curves shown in Fig. 1 may be drawn, the signals received from aerials A, B on a plane P2 moving along a curve R3, say, being always 120 degrees out of phase. To enable a plane to follow such a curve, which approximates a straight line at some distance from the aerials, means are provided on the plane for comparing the phase of the signals received from the two aerials. If the aerials were energized at the same frequency, it would be impracticable, by directional means, to separate the two signals at a substantial distance from the aerials and therefore one aerial is energized at double, or other multiple of, the frequency of the other, so that the signals can be selectively received. By frequency-multipliers, the frequencies are made identical before their phase is compared. Receiver on plane, Fig. 5. The signals of higher frequency, selected by a tuned H.F. amplifier 9, 11, 14, 19 with A.V.C., have their frequency doubled by a frequency-doubler 33, 34 and are further amplified by valve 39. The signals of lower frequency, selected by a tuned amplifier 9<1>, 11<1>, 14<1>, 19<1>, have their frequency quadrupled by a frequency-multiplier 33<1>, 34<1>, and are further amplified by valve 39<1>, so that the H.F. currents in the output circuits 40, 40<1>, whose phase is to be compared, are of the same frequency. The output of circuit 40' is connected to the anodes of two rectifiers T1, T2, the cathodes of which are connected to opposite ends of the divided secondaries 47, 48 of the output circuit 40. Resistances 56, 57 connect the other ends of the secondaries 47, 48 to the circuit 40<1>, and act as load resistances for the rectifiers T1, T2, these resistances being connected in series in a circuit 58 connected to the input circuit of a valve 60 forming one arm of a Wheatstone bridge 60, 62, 63, 64, a galvanometer 61 being connected across one diagonal of the bridge. Potentials proportional to the vector sum of the signals in the output circuits 40, 40<1> are thus applied to one rectifier T1, say, and potentials proportional to the vector difference to the other rectifier T2, corresponding direct currents flowing in the resistances 56, 57. The potentials across these resistances oppose each other in the circuit 58, so that the galvanometer 61 is controlled by the difference between the currents in the rectifiers T1, T2. If the currents in the output circuit 40 are in phase quadrature with those in circuit 40<1>, the resultant currents through the rectifiers T1, T2 will be equal, and no current will flow in the circuit 58 and the galvanometer 61 will point to zero. If, however, the currents in the output circuits 40, 40<1> are not in quadrature, the galvanometer needle will be deflected proportionately to the phase difference. As so far described, zero position of the galvanometer corresponds to phase quadrature of the currents in the output circuits 40, 40<1> and therefore to the currents in the aerial. But the operation of the invention depends upon maintaining equality of phase in the currents received from the two transmitters, and in order that zero indication on the galvanometer may correspond to equality of phase, the phase in one of the channels is deliberately varied, as by a condenser 67. Such a change in phase is multiplied by the frequency multiplier 33<1>, 34<1>, so that the condenser 67 will not substantially detune the channel in question, but will make the output from 40<1> normally 90 degrees out of phase with that from 40, so that where the plane is one course the galvonometer pointer will be at zero. Modified receiver, Fig. 7 (not shown). In order that the course along which the pilot will be guided can be selected at will, additional variable condensers may be connected in the grid and plate tuned circuits of the valve 19<1>, Fig. 5, so as to provide an additional phase shift corresponding to the course desired. An auxiliary oscillator is provided on the plane for calibration of these additional condensers. Alternative system, Figs. 8'to 12 (not shown). In this system three aerials A, B, C are used, aerials A, B being spaced one wave-length apart and energized 180 degrees out of phase, whilst aerial C is energized at a harmonic frequency. The receiver resembles that shown in Fig. 5, one channel receiving the waves from aerials A and B, and the other those from aerial C. The arrangement is such that the phase relation between the resultant signal produced by the simultaneous reception of signals from aerials A and B and the signal from aerial C will be either 180 degrees or zero, depending on whether the plane is on one side or the other of the " on course " line. Thermionic amplifiers. In order to maintain phase stability, the grid-bias of valves 11, 14 is derived partly by cathode resistors 22, shunted by condensers, and partly by unshunted resistors 24.