No power supply, energy saving and environmental protection. It can be used to test the efficiency of antenna or ground wire. The device is simple, a pair of coils, a variable capacitor, a geophone, a fixed capacitor and a pair of headphones constitute a practical ore machine. No power supply, safe and environmental protection, good sound quality. This product is FM mineral radio. The energy of electromagnetic wave is extremely limited. If you can't hear the sound, please repeatedly find the right place to listen. Our shop can't guarantee that you can listen to the radio in your place normally (it is recommended to listen within five kilometers from the launching tower), but it ensures that any equipment has no quality problems in the circuit. Note: Local test machine can receive two radio stations (because there are only two sets of FM broadcasting signals in the locality), because the buyer's geographical location and the strength of the radio transmitting signals are unknown parameters, so after receiving the radio, the buyer may appear many radio stations, series stations, few radio stations, or simply silent and other phenomena. So those who do not have certain basic knowledge and practical ability, please think twice about buying, thank you for your understanding and support! Color: As Shown Material: plastic Package Contents: 1 * Ore Radio with current meter