ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / The tracking modulation index (Km) is a key performance parameter for any autotracking antenna and should especially be considered for classically difficult targets such as missiles and/or fast moving aircraft. Antenna subsystems are typically characterized by their gain to temperature ratio (G/T) to optimize receive data bit error rates (BER) for distant targets. One important parameter often overlooked for telemetry autotracking antennas is a graded value for the available tracking modulation index (Km) that is common in radar autotracking applications. Tracking modulation performance is a major contributor for minimizing the antenna pointing error during an autotrack mission. Autotracking radar antenna specifications typically include tracking modulation as a major design parameter, many receive-only autotrack antennas used for telemetry applications do not consider this important parameter for the intended tracking mission which may result in poor autotracking performance. This paper investigates the effects of tracking modulation levels on system pointing errors for various classes of feed topologies.