AM radio tuner with HF amplifier stage - has aerial circuit output signal applicator to amplifiers with high and low gain respectively

摘要

The high frequency amplifier stage has an output line to a mixer stage, as well as input lines from an aerial circuit and a source of automatic amplification control voltage, proportional to the level of the signal output in the aerial circuit. The latter circuit output signal is applied directly in parallel to a high and low rate amplifier respectively. The amplifier stage has a fixed bias device for switching-on the high gain amplifier and for switching-off of the low gain amplifier, using the biasing voltage on absence of any signals from the aerial circuit. An applicator feeds the automatic amplifying control voltage to the circuit controlling both amplifiers. Thus the amplifying effect of the high gain amplifier is considerably reduced and that of the low gain amplifier considerably increased in response to the increase of the automatic amplifying control voltage.