1,159,138. Angle modulation. SOC. ITALIANA TELECOMMUNICAZIONI SIEMENS S.p.A. 20 Jan., 1967 [7 March, 1966], No. 3162/67. Heading H3R. A phase modulation circuit comprises a transformer T having a tapped secondary winding to which is connected a resistor R in series with a voltage dependent capacitance e.g. varactor diode D. The carrier is applied to the transformer primary, and the modulated output is derived between points A and B. In a first modification Figs. 2a, 3 (not shown), greater phase swing is obtained by including an inductance (L) in series or in shunt with capacitance D. In a second modification Fig. 4a (not shown), resistive losses which may give rise to amplitude modulation are compensated by including a resistor (r) in series with the capacitance D and adjusting the tapping point on the transformer. In further modifications linearity is improved by the use of two varactor diodes (D1, D2) each in parallel with an individual inductance (L1, L2) to form two resonant circuits tuned above and the carrier frequency. These two parallel circuits are connected in series with each other, the connecting link between them being from the ends of the two inductors Fig. 5 (not shown), or from tapping points on both or one of them Figs. 6a, 6b (not shown).