Voltage of 9V, Current 2 ~ 6mA, device parameters as shown in Figure shows, BG1 to 9018, BG2 for the C1959 (it can be 9018, but the power is very small, if it is D-40 can be extended to 1,000 meters from the radio, D -40 hard to get at the electronics store.), L1, L2 in the 0.5 to 0.5mm magnet wire around the rod 4 and 3 on the ring, the working voltage can be increased to 12V, so the distance can increase the launch, but the frequency will change The whole circuit is best to use battery-powered, can reach the best sound quality and frequency stabilization effect, turn off the debugging work BG2, to set your desired frequency, and finally open the BG2 regulate the power circuit. The circuit I am using BG1 – D40, BG2 – C1970 works well, voltage 12V, BG1 Voltage 6V, a distance of 3,000 meters (directional test). If you want to use D-40, you should pay attention to D-40 of the operating voltage is 6V! Best to put in a tin of this circuit, the input plus a decline by the network.