Hearing Aid Phase II-C :Waveguide Study

        The Hearing Aid Phase II-C Study used a 900 MHz waveguide to test 34 hearing aids against a 900 MHz RF signal 80% amplitude modulated with a 1 kHz sine wave, and against a TDMA-50 Hz (IS-136) phone. The input referenced interference level (IRIL) was plotted as a function of RF field strength and hearing aid alignment. Results confirmed those obtained by the National Acoustic Laboratories of Australia (NAL) with respect to curve shape and the square-law detection property (IRIL increases linearly with RF field strength at a ratio of 2:1). The hearing aids showed a broad range of immunities to RF signals. Phase II-C verified the importance of determining: proper test measures and their effectiveness in achieving compatibility, factors that affect measurement variability (repeatability), the criticality of orientation, and solid, scientifically-based test procedures using the proper equipment.