It is red when it is transmitting - 40°C temperature control fan. When the temperature is below 40°C, the fan does not work Product Parameters: - Product name: RF Power Amplifier - Input power: 1-5W - Modulation modes: DMR, C4FM, DP MR, CW, FSK, P2S, and FM - Transmitting frequency: 400-470MHZ (UHF) - Receiving frequency: 50-1000MHZ - Operating mode: half-duplex (in the transmit state, it cannot receive) - Receiving loss: -1DB ±0.4 - Output power: 20W;30W;40W;55W;80W - Power supply voltage: DC 10-14V - Standby current: 10-30MA - Heat dissipation mode: 40°C temperature control air cooling - Product size: 130 x 104 x 60mm/5.1 x 4.1 x 2.4 (LxWxH) - Product weight: 880g/1.9lb Package Included: - 1 x RF Amplifier. Usually it costs about 30USD-50USD. If you receive the item that not satisfied or defective, please do not open case and kindly notify us within 30 days.