Propagation Analysis of Signal of Opportunity Measurements in Green Bank

Ryan S. McCullough , Todd R. Schumann, and William Kozma Jr.

Abstract:

Very high frequency propagation measurements were obtained from signal of opportunity transmissions collected during public safety communications field campaigns within the National Radio Quiet Zone surrounding Green Bank, West Virginia. Measured path loss was then compared with predictions from the Irregular Terrain Model in complex, forested terrain. The propagation measurements consisted of a series of week-long field measurements campaigns using fixed very high frequency transmitters operating at 169.5375 MHz and a vehicle-mounted calibrated receiver, collecting received power measurements over extensive drive routes. Received signal levels were converted to basic transmission loss and compared against Irregular Terrain Model median predictions and free-space path loss estimates. Across the measurement campaign, the Irregular Terrain Model was found to systematically under-predict measured path loss by a median of approximately 13 dB. The observed discrepancies are attributed primarily to foliage attenuation and terrain diffraction mechanisms beyond the double knife-edge model incorporated within the model. In a smaller subset of cases, the model over-predicted path loss, likely as a result of terrain-induced signal enhancement not captured by the model. These results provide empirical context for the use of the Irregular Terrain Model in heavily forested, mountainous environments and could inform future planning for public safety communications systems within the National Radio Quiet Zone.

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