A plurality of remotely readable sensor apparatus and reader systems for collecting data frames from all apparatus within the reader field of view. Each sensor apparatus converts one or more environmental observable into information signals, converts the information signals into digital data and appends other discriminating digital data as desired to form a digital data frame. The state of a diode, connected to an antenna with the digital data frame, is modulated and a timing apparatus controls the digital-data-frame start times. The modulated states of the diode connected to a sensor-apparatus antenna are chosen so the angle of the antenna reflection coefficient is modulated between two values separated by approximately 180 degrees, so a carrier signal received by the antenna effects a bi-phase modulated signal containing the digital data frame that is reflected by the sensor-apparatus antenna toward the reader receiver antenna.