Airborne VHF environment noise measurements

Environment noise can be a limiting factor for airborne military command and control communications. This paper describes the techniques and results of noise measurements conducted in the VHF frequency band, as observed from an airborne C-130 aircraft operating over the state of Arizona. These measurements were performed to provide a better understanding of the noise environment applicable to VHF radio communications on the aircraft. The measurements were collected on several occasions using a VHF blade antenna mounted on the bottom of the aircraft. A modified surface-noise model is described to predict median noise levels at the aircraft altitude. In the VHF-FM band, median noise levels over rural Arizona were 4 to 5 dB above model-predicted levels. These levels of airborne VHF-FM noise will impact radio operation on the aircraft, especially in the lower portion of the band. In the VHF-AM band, noise levels were too close to the measurement noise floor to accurately determine noise levels. Because of the much lower level, however, airborne VHF-AM noise is not expected to have a significant impact on radio operation. A single measurement trial was also collected in the VHF-FM band near Phoenix during the evening rush hour. Measured noise levels were 17 dB above median values encountered over rural Arizona. The implication for VHF radio operation is that noise levels during certain times and operating locations may be significantly higher than normally encountered values.