2pcs FM Transmitter Pickup Module Professional V4.0 FM MIC Wireless Sound Transmitter for FM Radio 0.7‑9V Item Type: FM Transmitter Pickup Module Material: PCB Operating Voltage: Ultra Wide 0.7V to 9V Frequency Adjustment Range: Wider Than 88-108MHZ Transmitting Distance: 9V Work, Using 70cm/27.6in Wire for Antenna, Open Place Transmitting Distance of 50‑100m/ 164.0‑328.1ft, The Actual Depends on the Environment The Relationship Between Operating Voltage (Volts) and Supply Current (mA) and Transmitting Power (dBm) is as Follows: 9V, 24 mA, 10.2 dBm (That is, 11 mW) 8V, 21 mA, 9.5 dBm 7V, 19 mA, 8.5 dBm 6V, 17 mA, 7.1 dBm 5V, 14 mA, 6.1 dBm (Approximately 5 mW) 4V, 12 mA, 4.5dBm 3V, 9 mA, 2.2dBm 2V, 6 mA, -1dBm (~1 mW) 1.5V, 4.2 mA, -4 dBm (About 0.5 milliwatts, the general home environment is enough to transmit, green radiation is small!) 1V, 2.4 mA, -9 dBm 0.7V, 0.9 mA, -20 dBm (That is, 0.01 milliwatts)