Patent GB-438809-A (GB)
Abstract: 438,809. Wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London. (Wilmotte, R. M. ; 41, Park Row, New York, U.S.A.) May 25, 1934, No. 15694. [Class 40 (v)] [See also Group XXXVI] A radio transmission system comprises a plurality of aerials energized from a common source, each aerial being energized through a path which includes a coupling device such that the ratio of its input to output voltage is constant irrespective of changes in aerial impedance. The invention relates particularly to directional aerial systems and has for its main object the elimination of variations in aerial impedances due to snow, rain, &c., causing changes in the phase relationshp of the various aerials of the system. Fig. 1 shows an arrangement of two aerials A1, A2 fed from the transmitter output OC through coupling systems E, D, C, B, and transmission lines N, M. The two systems are connected at points P1, P2, 01, 02 through an anti-reaction coupling F12 and a phasemetering system G12 respectively. The coupling devices at B or C for either aerial may take the form of two series impedances ZA, ZB, and a shunt impedance Z<1>C (Fig. 2) where constant voltage ratio only is required ; for corresponding current conditions a second shunt impedance Z<1>D is provided. The Specification establishes that the required voltage conditions obtain when ZAZB + ZBZ<1> C + Z<1>CZA = O. In practice these impedances are almost pure reactances of the type shown in Fig. 3a. Since for this circuit, the above equation is only satisfied for a single frequency, where the working frequency is not predetermined a series condenser is inserted in the circuit l1, l2, ANT. Equations concerning the conditions of couplings C1, C2 are also given, taking into account the transmission lines N M. The couplings D1, D2 are inserted to bring the voltage at P1, 'either in phase with or in phase opposition to the voltage at P2 when a single aerial is excited from OC. Coupling F12 is then used to balance out the voltage so that the unexcited aerial produces no interference effect. The couplings E1, E2 produce the required phase relations in aerial excitation after the phase shifts due to the other couplings have been taken into account. Fig. 5 shows a method of measuring phase differences between 2 circuits such as at G12. The apparatus is simply a thermionic voltmeter comprising a diode T3 and milliammeter A coupled to the differentially combined output TA of valves T1, T2. Each valve has independent volume control and switches are provided to cut out T1 or T2 in turn so that readings of A depend on voltage across 01 or 02. The controls are adjusted until the two balance and with both valves operative the voltage in IC is proportional to the phase difference between 01 and 02. The invention is also applicable to prevention of distortion in transmission due to change of sign of one side band. This is accomplished by causing the phase displacement between aerials to vary with frequency and the impedances of Fig. 2 may so be constituted that the rate of change of reactance varies with frequency. For small adjustments the arrangement of Fig. 7 may be used. The two variable condensers are ganged so that as the capacity of one increases the other decreases ; the total phase-shift is unchanged but the rate of change of phase-shift with frequency varies.