The working voltage is 9V, the working current is 2~6mA, and the component parameters are as shown in the figure. BG1 is 9018 and BG2 is C1959 (it can also be 9018, but the power is small. If it is D-40, the shooting distance can be expanded to 1000m, D -40 is difficult to buy in the electronics store.), the enameled wire with L1 and L2 of 0.5mm is wound around 4 and 3 turns on a 0.5 round bar, and the working voltage can be increased to 12V, so the distance of the launch can be increased, but the frequency will change. The whole circuit is best powered by battery, which can achieve the best effect of sound quality and frequency stabilization. When debugging, first turn off the work of BG2, adjust the frequency you need, and finally turn on the BG2 circuit to adjust the power. This circuit I use BG1--D40, BG2--C1970 effect is very good, voltage 12V, BG1 working voltage 6V, distance is 3000 meters (directional experiment). If you want to use D-40, please pay attention to the working voltage of D-40 is 6V! It is best to install the circuit in an iron box with a fading reduction network at the input. HA series hood is suitable to small heavy duty connectors, it is widely used in machinery, wind energy, rail transportation, power systems, photovoltaic industry, communications industry, engineering equipment and other fields. Heavy Duty Connector is designed for modular production pre-wiring and satisfying severe environmental conditions, applied in rail transit,industrial automation and equipment manufacturing fields. Compared with traditional wiring methods,use of heavy duty connector can reduce site wiring operation after equipment or vehicle leaves the workshop,enhance production efficiency and reduce quality risk of site wiring. Ha Series Connector,4-Pin Heavy Duty Connector,3 Pin Heavy Duty Connector,Industrial Heavy Duty Kunshan SVL Electric Co.,Ltd , https://www.svlelectric.com