Squitter refers to random pulses, pulse-pairs and other non-solicited messages used in various aviation radio systems' signal maintenance.
These used a superregenerative receiver which greatly amplified input signals using positive feedback.
An automatic gain control system on subsequent models cured this problem.
In the TACAN system, signal strength variation due to rotation of the transmitting beam (amplitude modulation) determines the course bearing function.
This function would be lost without a constant 2700-4800 pulse-pairs per second, carrier-like signal in cases of low or no interrogating aircraft.