Attached is a schematic of the variable IF circuit. ?The RX and TX voltages are about 12V, so I used a resistor network to keep the applied voltage to about 1 to 9V because that is the usable range for these diodes.
The 4.7K resistors that feed the voltage to the VVC diodes could be 10 or 20 K, or what have you, as there is very little current needed.
Tom W1EAT
