Patent GB-506096-A (GB)
Title: Improvements in or relating to circuits for modulating high frequency oscillations
IPC: H03F1/06
Filed: 1938-04-28
Abstract: 506,096. Modulating systems. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. April 28, 1938, No. 12773. Convention date, May 20, 1937. [Class 40 (v)] In a high efficiency modulating arrangement the carrier is supplied by an unmodulated valve stage to the load and modulation is provided by a stage comprising one or more valves which supplies high frequency power to the load in the half-periods of rising modulation and absorbs power during the half-periods of falling modulation. The valve R1, Fig. 1, operating with optimum efficiency supplies carrier from the source Ug1 to the load R which is connected through the series tuned circuit L1<1>, L1<11>, C1<1>, and the tuned circuit L1 Cl passes undesired harmonics to earth. The couplings LK2, LK3 transmit voltage to the anodes of valves R2, R3 which serve for the supply of modulation power. The coupling coils LK2, LK3 form series tuned circuits with condensers CK2, CK3, and the tuned circuits L2 C2, L3 C3 and blocking condensers CB conduct undesired harmonics to earth. The valves R2, R3 are controlled in push-pull as regards high frequency and modulation frequency (Ug3, Um3, Ug2, Um2) on the grid side and the bias Ug is such that it almost completely cuts off the valves. To allow for the 90 phase shift through the tuned couplings the control voltages for valves R2, R3 are shifted 90 with respect to the carrier voltage drive on R1. During the rising half-cycle of modulation, valve R2 passes current and supplies to the load through the coupling LK2 a voltage which aids the voltage supplied from the valve R1. During the falling halfcycle of modulation valve R3, which is given no direct anode voltage + Uz unless the degree of modulation required is very high, consumes power from the load, producing an opposing voltage through the coupling LK3. The stage providing the additional modulation may, instead of being connected in series with the load as in Fig. 1, be connected in parallel with it. In the arrangement of Fig. 5 (not shown) the valves R2, R3 act on a common tuned circuit across which the load is connected ; the carrier valve R1 being connected to the load over a quarter-wave-length line or similar network. The separate coupling of valves R2, R3 to the load through coils LK2, LK3, may be arranged with the same parallel connection, Fig. 6 (not shown). In the embodiment of Fig. 7, the carrier power is supplied to the load R by the unmodulated valve R1 as before, but the stage supplying the modulation power is a single valve R2 controlled by modulated high frequency with suppressed carrier. A series connection by coupling from L1 to L2 through an intermediate circuit LK1, LK2, CK is shown, but a parallel connection of R2 to the load may be effected and the valve R1 may be coupled to the load over a quarter-wavelength feeder, Figs. 8 and 9 (not shown). To compensate for the phase change in the coupling circuits, 90 displacement must be introduced between the grid voltage Ugl, Ug2, as before. A push-pull carrier 'suppression modulator may be used in place of valve R2 with a suppressed carrier control, in which case the circuit is similar to that of Fig. 1, except that the valve R3 receives a normal anode voltage. Reference has been directed by the Comptroller to Specifications 326,375, [Class 40 (v)], and 483,883.