GB555384A - Improvements in radio-transmitters - Google Patents

Abstract

555,384. Modulating systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and PRICE, T. H. Jan. 16, 1942, No. 690. [Class 40 (v)] In a radio transmitter of the kind in which two phase-modulated channels jointly feed an aerial or other load to produce an amplitude-modulated wave, an impedance-inverting network or device is interposed between each channel and the load. In Fig. 3, the two channels are represented by the valves A, B and the load by a resistance R, the impedance-inverting networks NA, NB being interposed between the load R and the tuned output circuits TA, TB of the valves. The adjacent coils of the networks NA, NB may be assimilated into a single coil connected across the load R, Fig. 6 (not shown). The valve anode circuits may be differentially mistuned in order to give an effective resistive load to the valves, e.g. by ganged control of the inductances of the circuits TA, TB, or of the series condensers of the networks NA, NB. The carrier applied to the valves A, B in the unmodulated condition may be separated in phase by 160 degrees and the modulation may shift the phase separation between the limits 140 ... 180 degrees. In some cases, the negative half-cycle of modulation may carry the phase separation beyond 180 degrees. Fig. 11 shows a complete circuit arrangement. Modulating voltage mf is amplified by a resistance-coupled amplifier MA, including a feed-back system of the kind described in Specification 547,890. The output valve A7 supplies to the leads MF voltages in phase opposition which are applied to the grids of a balanced modulator V1, V2. Carrier in phase opposition is also applied to these grids by the transformer T2 fed from the carrier amplifier V4. The modulator V1, V2 may be unbalanced by differentially biasing the grids by a potentiometer PT. The output valves VA, VB, which feed the load R through an impedance-inverter II, have a bridge circuit p, q, r, s connected in their grid circuits, the ends B, C of the vertical diagonal being connected to the grids and the end E of the horizontal diagonal to the cathodes and earth. The modulated output of the valves V1, V2 is applied, through a lead MC and earth, across the horizontal diagonal A, E and pure carrier in quadrature phase is applied through a lead RF1 and a transformer T1 across the vertical diagonal BC. The relative phase of the carriers supplied to the leads RF1, RF2 by the valves V3, V4 is adjustable by a condenser CD in their grid circuits. When the modulators V1, V2 are operated in balanced condition, the radiation is of the suppressed-carrier type ; unbalance results in the addition of pure carrier to the radiation. A monitor circuit MR may be provided similar to that described in Specification 540,245.