Fallout 4 powering up radio transmitter [duplicate]
The radio transmitter requires 10 power to turn it on. A small generator only produces 3. You will need 7 more power to turn on the transmitter. Either build 3 more small generators and attach them all together, or build a different type of power source. As long as the total power reaches 10, you will have enough. After you have enough power, activate the controls to turn on the transmitter.
Video for reference: