Noise Blanker

A noise blanker is indispensable for im- proving the reception of very weak signals on the SW bands. In most com- munication receivers, the selectivity of intermediate frequency (IF) filters cause interfering pulses to be widened, blot- ting out the wanted signal. It is useful, therefore, to suppress interference before this can wreak havoc in the IF sections of the receiver. The 455 kHz IF signal is first buffered in T2, and then processed separately in two circuits. The lower section of the circuit is a TCA440 based receiver for the interfer- ing pulses. The TCA440 is in itself a vir- tually complete receiver, since it com- prises an RF amplifier, a mixer, and an IF amplifier. All stages in the latter are used since pin 4 is grounded here. The pulse receiver has its own AGC (auto- matic gain control) to ensure effective suppression of relatively weak inter- ference also. Preset PI and poten- tiometer P2 enable precise adjustment of the noise blanker for various levels of interfe...