An electrical, magnetic or electromagnetic delay line self oscillator is described with a delay line arrangement, an oscillator control circuitry, and a frequency selection impedance connecting the delay line arrangement and the oscillator control circuitry and presenting an impedance to the delay line arrangement. The oscillator control circuitry includes an amplifier, a non linear amplitude control element (N-LACE) such as an active device with a negative differential conductance that provides an output amplitude has a negative second derivative with respect to an input signal, and a driver. The modal characteristics of electromagnetic delay lines can thus be exploited across a wide range of instrumentation applications, and a means is provided to enhance the achievable functionality and/or performance of the instrumentation without the need for expensive additional electrical hardware or electronics.