Conical scan and monopulse antennas are susceptible to interference from weather phenomenon and stationary objects. The resulting interference can produce feedback signals that move the antenna beam away from the aircraft. This can produce an unreliable antenna position when the antenna is aimed too near the ground or too near to heavy weather. Systems with no Pulse Doppler tracking mode may remain aimed at irrelevant objects like trees or clouds. Constant operator attention is required when there is no Doppler signal processing.