GB881548A - Combining system for diversity communication systems - Google Patents

Abstract

881,548. Radio diversity receiving systems. STANDARD TELEPHONES & CABLES Ltd. May 15, 1959 [May 22, 1958], No. 16747/59. Class 40(5). A radio diversity receiver has a circuit for combining two carrier waves Va, Vb, Fig. 2, which have the same frequency, but which may have been transmitted as different frequencies, and which comprises a hybrid circuit 20 including a transformer 25 to which one carrier Vb is applied at terminal 24, and producing two voltages +V 2 and -V 2 therefrom, a phase detector 22 to which these voltages +V 2 and -V 2 are supplied together withthe other carrier Va, and the phase of Va and/or Vb is controlled by the output of the phase detector so that a constant phase difference exists between them. The phase difference of Va and Vb is maintained at 90 degrees, Va being applied through terminal 23 and delay line 33a, which introduces a further 90 degrees phase difference, to one end of primary winding 30, V 2 being applied to the other end so that the signals are combined and applied to output terminal 32. In a frequency diversity receiver the local oscillators 7, 13a, Fig. 1, operate on different frequencies, the phases of these oscillators being controlled by the output of the phase detector 22. The I.F. amplifiers 8, 14 have equal gains and receive an A.G.C. signal derived from the combined signals in circuit 21.