Canadian aeronautical satellite tests using the ATS-6 satellite, January 1976

The ATS-6 satellite was used to compare the performance of several voice modulation techniques and two antenna systems installed in an airborne terminal. For these tests, improved versions of a voice modulation technique based on a delta encoding/PSK modulation and a technique based upon the transmission of the PSK modulated zero-crossing transitions of the audio signal were tested against a reference narrowband frequency modulation system under varying conditions of carrier-to-noise density ratio and carrier-to-diffuse multipath ratio. The delta and zero-crossing encoding units proved to be very reliable and yielded exceptionally good intelligibility scores. The aircraft antenna system included a nine-element linear phased array mounted on the top centerline of the aircraft and two cavity-backed slot dipole antennas mounted on the shoulders of the aircraft. A significant improvement over previous testing was the incorporation of an automatic beam steering unit which worked in conjunction with an onboard inertial navigation system.