The noise limiter is a circuit to reduce man made noise interfering with (AM) broadcast signals. In the simplest way, it just consists of two anti-parallel diodes (two semiconductor diodes or two systems of a duo diode valve). In case of voltage peaks, one or the other diode becomes conductive and the disturbing crackle is suppressed.
Some semi-professional shortwave receivers from the amateur radio sector are equipped with more complex circuits to eliminate interference; especially the Russian over-horizon radar of the 1980s led to broadband interference pulses on the shortwave bands. That gave it the name „Woody Woodpecker“ - a very annoying companion of all shortwave listeners in the eighties and nineties.