An investigation into transistor cross-modulation at VHF under AGC conditions

The cross-modulation behavior of a transistor is studied for the case where it is operated in the VHF region and gain control is effected by driving it into saturation. It is shown that the observed increase in cross-modulation can be attributed to the fact that in the saturated condition the stored charge in the transistor will depend noulinearly on the collector current. The cross-modulation factor is calculated assuming an arbitrary functional relation between stored charge and current. A relation between the cross-modulation factor and the change of the cutoff frequency with current then will exist, allowing experimental verification. Close agreement is found between measured and calculated values.