A vehicle communicates with a remote key fob while ensuring an RF environment is sufficient to maintain adequate power from an RF-harvesting power supply that allows the fob to operate without a battery. The vehicle has a receiver adapted to detect a backscatter communication signal from the fob. A harvesting emulator in the vehicle is responsive to ambient RF around the vehicle to duplicate a concurrent response of the fob power supply. A vehicle-powered RF transmitter is activated to broadcast energizing RF radiation around the vehicle when the duplicated response is below a threshold.