. Airborne radar. Airplanes; Guided missiles. 8-32] ACCURACY REQUIREMENTS ON ANGLE TRACK STABILIZATION 463 alternative to returning to the search mode would be to replace the average level of the stabilization loop command, ordinarily the radar error signal, with a fixed d-c voltage to eliminate the noise. Unfortunately, this requires extra mechanization which may not be worth the additional space and complexity. However, during the fading period, it is necessary to provide sufficient antenna space stabilization, with the stabilization control loop, to keep the positional deviation incident to
. Airborne radar. Airplanes; Guided missiles. 8-32] ACCURACY REQUIREMENTS ON ANGLE TRACK STABILIZATION 463 alternative to returning to the search mode would be to replace the average level of the stabilization loop command, ordinarily the radar error signal, with a fixed d-c voltage to eliminate the noise. Unfortunately, this requires extra mechanization which may not be worth the additional space and complexity. However, during the fading period, it is necessary to provide sufficient antenna space stabilization, with the stabilization control loop, to keep the positional deviation incident to aircraft disturbance motion an order of magnitude lower than the maximum allowable deviation. There- fore, for the illustrative case depicted by Fig. 8-40, the peak positional error incident to aircraft motion should be less than °.^^ Although this is not as much attenuation as is required to reduce the rate signal errors, it may not be so in all cases. Usually, it is necessary to check the amount of stabilization needed for each type of error to determine which will require the greatest amount of attenuation. Stabilization Accuracy Required to Prevent System Instability. As mentioned in Paragraphs 8-25 and 8-32, antenna stabilization is needed, especially in a system with autopilot control, to prevent system instability incident to coupling between the aircraft space commands from the antenna gyros and the resulting antenna motion from the commands. Unlike the human pilot, the autopilot responds to all signals. Ordinarily, it does not learn to reject the signals generated by the coupling between the aircraft and antenna motions. Since this is a form of positive feedback (an undesired or parasitic loop) it is necessary to keep the magnitude of this loop gain less than one-half at all frequencies to ensure that instability will not occur.^*. Fig. 8-41 Coupling Between the Air Frame and the Antenna. G2 = amplifier, actuator, antenna; Gs = rate gyro; Gc = fire-control compu
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