Modeling of Audible Noise with DSB-AM due to Helicopter Rotor Modulation
Terry R. Vogler
ARINC Engineering Services
ARINC’s recent aircraft integration work required the installation of multiband radios that were not aircraft-certified. Other installation details were typical for helicopters, including the use of Sensor Systems wideband aircraft blade antennas. During installation tests, audible rotor modulation noise was noted when transmitting or receiving with the top-mounted antenna using DSB-AM in the air traffic control (ATC) frequency bands. This noise was not noticeable on a bottom-mounted antenna. Because changes to the radio circuitry were not feasible, an alternative mounting location for the top-mounted antenna was desired. A simulation method was needed to compare the susceptibility of different mounting locations to rotor modulation. Using FEKOTM together with Rhinoceros® and MATLAB®, a multistage simulation was developed to move the helicopter rotors; calculate the transmitted fields at a set radius; and mix the field modulation with audio samples. Field fluctuations are evaluated to provide insight on the modulation effect and the depolarizing effects needed in the propagating and receiving environment. A comparison of the changes in the audio spectrums for different antennamounting locations indicates the overall susceptibility of the location to rotor modulation.
25th Annual Review of Progress in Applied Computational Electromagnetics
2009
March
167-172
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