a major improvement in stability and a small improvement in available gain for reception of cw radiotelegraphy is provided by the use of a separate oscillator, known as a "heterodyne oscillator" or "beat oscillator". providing the oscillation separately from the detector allows the regenerative detector to be set for maximum gain and selectivity - which is always in the non-oscillating condition. interaction between the detector and the beat oscillator can be minimized by operating the beat oscillator at half of the receiver operating frequency, using the second harmonic of the beat oscillator in the detector.