Experimental verification of compensation phenomena in oscillators with two multiple modes

The features of nonlinear processes in oscillators with two synchronous modes open up a new method of frequency stabilization, as in such oscillators the correlated normal frequency shifts of the same sign arising, for instance, due to temperature variations or active device reactance perturbations tend to compensate each other in respect of their influence on an oscillation period. This paper deals with experimental verification of the theory. Two cases of a harmonic ratio, 1:2 and 1:3, are investigated. The RF model used incorporates a transistor one-pole negative conductance active device loaded on a LC-filter with two multiple resonant frequencies. Both harmonic ratios provide easy and reproducible tuning at the compensation regime. The most remarkable demonstration of the discussed phenomenon takes place when the oscillator is overcompensated, as in this situation an oscillation frequency grows while a capacitor shunting the active device output is being increased. Frequency stability gain in excess of 40 dB in a rather wide range of parameters is registered in some tests.