doi: 10.6028/NIST.TN.1519

Christopher L. Holloway, Frank H. Sanders, and Paul M. McKenna

Abstract:

A study was performed to determine the increase in ambient electromagnetic field strengths that would result from a proposal to locate a cluster of terrestrial digital television (DTV) transmission towers in proximity to the Department of Commerce (DOC) Laboratories in Boulder, Colorado. The primary objective of this study was to assess the impact on a broad range of Federal Government research and metrology programs that depend upon the relatively quiet radio-frequency electromagnetic environment. Radio-wave propagation measurements were performed for two terrestrial DTV frequencies (533 MHz and 772 MHz), and used to verify predicted DTV electric field strengths obtained from the DOC Irregular Terrain Model (ITM). The measured data were also used to determine the variation in received signal strength over small distance intervals. Radio-wave propagation measurements were performed at both frequencies using two possible mountaintop transmitter locations, Eldorado Mountain and Squaw Mountain. The first (Eldorado Mountain) affords substantial line-of-sight coverage over the Boulder area, and the second (Squaw Mountain) affords only indirect (diffractive) coverage over the same area. The two propagation conditions from each site, direct and indirect, respectively, are compared to the ITM predictions. The relative variations in measured and predicted signal strengths are compared as a function of frequency and of propagation conditions. Measured and predicted data were found to be in close agreement. This provides confidence that the theoretical predictions of received signal strengths at given locations in the Boulder area are accurate. It was found that in some locations, the ambient field strengths for 1 MW of transmitter power from a single station will exceed 1 V/m.

Keywords: spectrum survey; propagation modeling; digital television (DTV); field strength measurements; Irregular Terrain Model (ITM); National Radio Quiet Zone (NRQZ)

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