Abstract: In order to provide for dynamic calibration of a radio altimeter which utilizes frequency modulated continuous waves having a triangular wave form, a selected frequency output of the altimeter is compared, during a calibration interrupt of the output of the altimeter, to a predetermine value for that frequency and if it differs, the frequency is adjusted to the correct value. Each frequency in the triangular wave is individually calibrated during separate calibration mode interrupts. Specifically, each frequency is calibrated by coupling a portion of the altimeter signal to a prescaler circuit and using the prescaler circuit in combination with a modulation frequency counter to input a value representing the frequency to a control microprocessor. The microprocessor then compares this value to a desired frequency and adjusts a value in a memory that is used to control the frequency output of a voltage controlled oscillator that is used to generate the frequency modulated continuous wave.

Abstract: To ensure that a radio altimeter indicates zero altitude when the aircraft is on the ground, an on-ground calibration system utilizes a calibration switch to initiate a calibration radio altimeter signal from the radio altimeter's transmitter section which is reflected off of the ground and received by the altimeter's receiver section. The time delay between transmission and reception of the signal is measured and a value representing the delay is stored in the altimeter's microprocessor. This value corresponds to zero altitude and can be used as the relative zero point for calculating altitudes of the aircraft when it is in flight.

Abstract: An aircraft mounted pulse radar unit transmits a low-energy, test output pulse and processes the resulting test return signal to determine the VSWR and whether the VSWR exceeds a predetermined threshold. If the VSWR exceeds the threshold, the unit prevents transmission of a nominal energy output pulse which might result in damage to the receiver due to an excessive energy level of the return signal. In one embodiment, the unit uses the VSWR to determine and enable output signals at reduced power levels such that energy levels of any return signals would be insufficient to damage the receiver.

Abstract: The invention of this patent is related to unit-to-unit performance matched radar provided by automatic compensation based on software mapping of calibration data over an dynamic operating range of temperature and radar return signals.

Abstract: A radar system includes a stabilization calibration arrangement wherein a module stores particular parameters for relating the radar system to a gyro which provides stabilizing data for the radar system. The storage module, the radar system and the gyro are mounted on the same mounting platform so that the particular calibration features remain with the mounting platform. With the arrangement described, the radar system is independent of the gyro and can be of a generic configuration as is advantageous for stabilization calibration purposes.

Abstract: The signal that controls the gain of a sensitivity timing control (STC) circuit is slimmed with a gain correction signal to compensate for gain variations introduced by items such as variations in the parameters of electronic components. A known test signal is injected into the STC circuit and the resulting output signal is measured. The amplitude of the gain correction signal is determined based on the difference between the desired output signal amplitude and the measured output signal amplitude.

Abstract: The frequency of a variable frequency oscillator in a pulsed radar is adjusted using samples of an IF signal. An initial frequency adjustment is made using a sample taken during RF transmission. This initial adjustment contains an inaccuracy introduced by the magnetron's activity. An additional adjustment is made using temperature dependent values stored in a memory. Yet another adjustment is made during the radar's receive time using signals reflected by targets.

Abstract: A weather display apparatus and method wherein the relative positions of weather information and reference marks are accurately displayed. Information obtained from typical airborne weather radars is distorted due to the use of imperfect beams, such as a conical beam. The distorted weather information is displayed to a pilot. At least one reference mark is also displayed on the display in positions in accordance with relative positions in the airspace and with a distortion factor.