Abstract: A hot wire anemometer circuit has a calibrate subcircuit and an operate subcircuit which are selectively invoked via a user-activate mode switch. The calibrate subcircuit includes a detector configured to compare an amplified sensor voltage with an amplified drive voltage and output an indicator signal when the two voltages match. The drive voltage is derived from a user-adjusted drive resistance of a bridge subcircuit. The operate circuit includes a feedback loop which provides a signal to a bride node of a bridge circuit. After a sensor is connected to the anemometer circuit, the drive resistance is adjusted until the indicator signal is produced, signifying that the circuit is tuned and impedances are matched to prevent oscillations. A slewing network protects the sensor by shorting the drive resistance upon switching the anemometer circuit to the calibrate mode from the operate mode, and gradually restoring the drive resistance when switching back.

Abstract: A hot wire anemometer circuit has a calibrate subcircuit and an operate subcircuit which are selectively invoked via a user-activate mode switch. The calibrate subcircuit includes a detector configured to compare an amplified sensor voltage with an amplified drive voltage and output an indicator signal when the two voltages match. The drive voltage is derived from a user-adjusted drive resistance of a bridge subcircuit. The operate circuit includes a feedback loop which provides a signal to a bride node of a bridge circuit. After a sensor is connected to the anemometer circuit, the drive resistance is adjusted until the indicator signal is produced, signifying that the circuit is tuned and impedances are matched to prevent oscillations. A slewing network protects the sensor by shorting the drive resistance upon switching the anemometer circuit to the calibrate mode from the operate mode, and gradually restoring the drive resistance when switching back.

Abstract: A system and method are provided that includes an aircraft secondary radar transponder activity detector that monitors an aircraft's transponder transmissions and activates an emergency locator transmitter to begin transmitting should the aircraft transponder transmissions cease to help locate an aircraft that may have become undetectable by conventional aircraft surveillance and tracking systems.

Abstract: An RF coupler is used to measure transmitted power and receiver sensitivity of an avionics RF transceiving system (e.g., a secondary radar transponder). The coupler physically mates with (e.g., by conformally enveloping) an airborne type blade antenna mounted to the fuselage of an aircraft. The construction and theory of operation of such a coupling device for coupling RF energy into an antenna is disclosed. The coupling device provides receiver sensitivity measurements and produces rectified pulses or DC levels for the purpose of measuring transmitter power. The system measures such parameters in the extreme near-field (e.g., about 0.1 wavelength) to simplify the measurements and to isolate the measurements from errors due to standing waves and the presence of other nearby objects.

Abstract: A frequency synthesizer takes advantage of the simplicity of the phase lock loop and the rapid settling time and spectral purity of direct methods of frequency synthesis. "Approximations" and resulting frequency output errors are controlled and optimized to provide high performance, low noise, rapid frequency acquisition and stabilization, wide frequency range, high frequency resolution, and high accuracy and stability. In one embodiment, phase locked loops provide an output frequency with a resolution considerably less than the reference frequencies due to the application of a unique direct synthesis method. Additional resolution (and correction of error due to the approximations) is obtained by slightly varying the frequency of the master reference frequency. As direct frequency synthesis does not suffer from the long lockup times associated with phase locked loops operating at low reference frequencies, such small frequency changes can be made almost instantaneously.