as a part of the collector load and by appropriate selection of resistor ra the oscillation amplitude is properly controlled thus a carefully controlled impedance is obtained this ensures that the loop gain is greater than 1 for small signals but drops to a value less than 1 for large signals in this case the transistors are never driven to cut off which ensures good frequency stability referring to equation 5 it may be seen that the denominator will tend to infinity together with the numerator and the loop gain will stay the same by putting in the resistor ra the value of the numerator of the loop gain equation is limited which forces the loop gain toward unity as the oscillator starts and then begins to run in making the computation for the loop gain based upon the parameters cited it is seen that the loop gain will be equal to 82 divided by the series resonant resistance r s 52 so that the circuit will oscillate for any crystal with a series resonance resistance r s less than 30 ohms referring now to fig3 it may be seen that the relative impedance of the piezoelectric crystal is the resistance r s at the series resonance frequency of the branch lcr s of the equivalent circuit shown in fig2 this impedance which is resistive is shown in fig3 to be the lowest value of impedance for the crystal thus it may be seen that the spurious frequencies will have a higher impedance than the series resonant resistance of the crystal and the oscillator circuit shown in fig1 will not oscillate at these spurious frequencies the oscillator output signal is obtained as a differential voltage from the collectors of transistors 14 and 16 and would appear on paths.