In this case, the NE602 is used in this superhet front-end configuration. Ul serves as a frequency conve
rter. L1/L2 is a broadband toroidal transformer. A tuned transformer may be used instead. The supply voltage is + 5 to +9 Vdc. Tl is tuned to the IF frequency. The typical IF frequency is 455 kHz. This circuit, depending on Ll, L2, and L3, should be usable in the frequency range from audio to 30 MHz. The varactor tuning diode can be replaced with an air-variable capacitor, if desired. Ll, L2 1:12 Turns Ratio Toroid (Broadband). L3 Resonates to L.O. Frequency with Dl capacitance. LO FREQ Desired received frequency Â± IF frequency.