Neighborhood Broadcast Fields
in Portland, OR

RF fields in highly populated neighborhood areas have been a source of public concern for many years. Prior to the construction of the KGON broadcast tower on Healy Heights in Portland, Oregon, Richard Tell Associates, Inc. was asked by the Planning Department of the City of Portland to conduct a comprehensive 'before' and 'after' study of environmental fields produced by the aggregate broadcast facilities. Prior to the new tower that consolidated most of the broadcast facilities at Healy Heights, a multiplicity of towers supported numerous high-power FM broadcast antennas, some at relatively low heights. A neighborhood RF field survey of the area included measurements at 171 different points in the streets of the neighborhood.

RF fields were measured in terms of spatially averaged values using a broadband field probe and meter with an attached data logger. The measurement approach consisted of determining the spatial average and spatial peak fields at each point with the observer facing the measurement location, sequentially, from each of four directions. This method permitted an assessment of the variability in measured field values caused by body reflections and helped to establish the typical uncertainty that is commonly associated with field survey measurements. These kind of data are useful for understanding how different individuals performing, presumably, the same survey can arrive at apparently different results (see Practical Applications of the ANSI/IEEE C95.1 Radiofrequency Exposure Standard by R. A. Tell, in Advances in Electromagnetic Fields in Living Systems, Vol. 2, ed. J. C. Lin, 255-274, Plenum Press, 1997).




An analysis of the field measurements taken before and after construction and operation of the new tower showed a distinct difference in the prevalence of higher level fields. After operation of the new tower, the accumulative percentage of measurement points exhibiting power densities certain values shifted downward and the maximum measured fields were approximately an order of magnitude lower.