Vactrols VTL5C2, VTL5C4 and VTL5C9

These photoresistors have a wide range of applications. Inside, an LED is optically coupled to a photoresistive cell with no electrical connection between them - so a small DC current through the LED remotely sets the resistance on the isolated side, with no galvanic path back to the control circuit. This optical isolation, combined with the ability to vary resistance over a wide range, makes vactrols well suited for RX antenna loading (such as K9AY or DHDL designs) and other variable-gain circuits. Their power handling is suitable for RX antenna use. To increase destruction resistance, we recommend adding a 2W resistor in parallel, with a value of 750Ω–1.2kΩ as needed - a bidirectional protection diode is another option. See the datasheets for more details.