Threshold circuit

This circuit can be used to control the resonant frequency of the tuned circuit, provide a signal to the receiver queue, and measure the antenna. The table gives the winding data for the plug-in coil L1. The size of the component values ​​is not very important. T2 is the 10000 ohm primary winding and the 2000 ohm secondary winding of the inter-transistor audio transformer in the instrument circuit. The junction field effect transistor a1 and the PNP type bipolar transistor are used in a common drain circuit.