Contention communications often requires a station to wait an inordinate amount of time before the station is able to transmit its data successfully. In a particular embodiment of the device, a plurality of X-ray sources, an X-ray detector, and an analyzer grating are attached to a rotatable gantry, while a ring-shaped phase grating is stationary. The protection system uses short, low-power tests pulses to determine the quality of an antenna load upon tuning the radio to an RF carrier frequency by transmitting the short test pulse. The opposed ends of the strap are connected to the back panel so as to form a loop for encircling a support like the headrest of a vehicle seat.