Power supply circuit for an active antenna of a vehicle radio

A circuit for supplying power to an antenna amplifier (4) of a vehicle radio, comprising

• a filter circuit (R1, C1;
• R3, C3) including a first transistor (T1) having a base, a collector, and an emitter;
• the collector-emitter path of said first transistor being interposed in a current path of said first transistor being interposed in a current path between an operating voltage terminal (U.sub.B) of the radio, through a first inductance (L1) and past a first signal terminal (K1), to an antenna bushing (A) of the vehicle radio;
• and
• a protective circuit, containing further transistors (T2,T3,T4) which, whenever a predetermined current is exceeded, blocks said first transistor (T1) and thereby cuts off power supply to an antenna amplifier (4) being supplied with power via said antenna bushing (A);
• said protective circuit having a control input (SE) for switching said circuit into one of two stable states;
• and
• wherein a measuring resistance (R10) arranged in said current path has a pair of terminals which are connected respectively to second and third signal terminals (K2,K3), from which information, about the type of attached antenna and about its operating state, can be picked up.