AM Crosstalk in Unified Carrier Telemetry Systems

Under the unified carrier concept several anglemodulated subcarriers are combined and PM on an RF carrier. As a practical matter in a hardware system the angle-modulated subcarriers will contain a certain amount of amplitude ripple. Conceptually, a subcarrier with AM ripple can be viewed as a constant envelope subcarrier with a continuously varying modulation index. It follows that a continuous transfer of AM between the components in the unified carrier spectrum will occur due to the varying envelope (modulation index) of any data subcarrier. This paper discusses in some detail the problem of crosstalk transferred to the PM carrier from a single subcarrier which is biphase modulated with pulse-code modulation (PCM) data. The implications to carrier false lock and tracking are studied. Analytic and experimental results are presented.