The oscillator comprises an amplifier stage followed by a phase inverting stage, whose output is connected through two feed-back circuits to the amplifier input. Positive feed-back is realised by a resistor, and negative feed-back through the oscillating circuit. The amplifier stage is established by the transistor (7) and the resistor (8), while the phase inverting stage consists of the transistor (10) and the resistor (9&11). The approach or insertion of a metallic suppression element (6) with respect to the oscillating circuit inductance (5) causes a variable suppression of the oscillating circuit which comprises the inductance (5) and a capacitor (4).
