GB596877A - Improvements in or relating to circuit arrangements for suppressing the carrier in amodulated carrier wave - Google Patents

Abstract

596,877. Modulating systems. SPERRY GYROSCOPE CO., Inc. May 3, 1945, No. 11299. Convention date, May 3, 1944. [Class 40 (v)] [Also in Group XXXV] A modulated carrier wave is relieved of its carrier component by applying it to two branched channels which are ultimately recombined in an output circuit, one channel including an amplitude-levelling valve and a variable-gain amplifier, the other including a phase-shifting network. The gain of the variable amplifier being automatically adjusted so that the pure carrier is balanced out at the output. The modulated carrier applied at terminals 11 feeds two channels 12, 13, the channel 12 including an amplifier 17 giving a gain which varies inversely with its input voltage, thus levelling the wave amplitude. After passing reversed limiters 18, 19, the wave is fed through a link circuit 22 and a tuned amplifier 15 to terminals 24 at which pure carrier may be taken off. The pure carrier is also fed to a combining coil 33. The other channel 13 includes an amplifier 26 and a phase-shifting network 27 which feeds carrier and side-bands into the coil 33 in such phase that the two carrier feeds are in opposition and tend to cancel out. Any residual carrier is detected by the balanced modulator 34, the valves 35, 36 being fed in push-pull from the coil 33 and in parallel from the link circuit 22. Any residual carrier present in the coil 33 gives an unbalanced D.C. voltage in the anode circuits of the valves 35, 36 which is used as automatic gain control bias for the amplifier 15 and causes a balance of pure carrier in the coil 33, so that pure side-bands are available at the terminals 32. The A.G.C. bias derived from the balanced modulator may be applied in opposite senses to the valves 15, 26 (Fig. 2, not shown).