Pilot signal detector for traffic information radio - has half-wave rectifier after primary of double tuned circuit and voltage doubler after secondary

摘要

The pilot signal detector has a half wave rectifier (20) in the rectifying stage (19) following the primary circuit (12) of an under coupled band pas filter tuned to the pilot signal. The rectifying stage (22) following the secondary circuit (15) is constructed as a voltage doubler. The two rectifying stages are connected together via a resistor (26) chosen so that in the absence of a pilot signal the two rectifying stages produce d.c. voltages of roughly the same magnitude but of opposite polarity. The advantage lies in reduced fabrication costs whilst still being able to detect weak pilot signals.