This configuration from a 1976 technical documentation shows how to use a varicap in a direct current tuning system using a shielded cable. The circuit can be implemented with varicaps from the BB series. Two 9 V batteries in series can be used in the supply to obtain a greater control range according to the varicap. The coil is that of the tuned circuit that must be controlled. A 100 k paraR1 potentiometer greatly increases the durability of the power supply.
