Vehicle detector with improved loop oscillator circuit

A vehicle detector oscillator unit comprising:

• a power terminal adapted to be coupled to a D.C. electrical power source;
• a ground terminal adapted to be coupled to an electrical ground source;
• an oscillator circuit adapted to be coupled to a loop, said oscillator circuit including a control input terminal for receiving a control signal from a control device for enabling and disabling operation of said oscillator circuit, an output terminal for manifesting oscillator output signals, and an oscillator transistor having a first terminal coupled to said output terminal and a second terminal;
• a gain control circuit coupled to said oscillator circuit for maintaining the amplitude of said oscillator output signals within a limited range, said gain control circuit including a biasing network coupled between said power terminal and said output terminal, said biasing network having an intermediate junction, and a transistor having a first terminal coupled to said second terminal of said oscillator transistor, a second terminal coupled to said ground terminal, and a gate terminal coupled to said intermediate junction;
• and
• a clamping circuit for eliminating ringing of said oscillator output signals when operation of said oscillator circuit is disabled.