Indoor Reception 'Impossible' to 'Non-Existent,' Say iBiquity and Greater Media

by Leslie Stimson, 07.13.2009

print rss

Greater Media and iBiquity conducted indoor elevated power reception tests using WKLB(FM), Waltham, Mass, as well. They took measurements at six locations with buildings chosen to represent different types of construction. This test is noteworthy because it used several buildings and multiple radios within the buildings, and because it involved a station whose signal covers an entire metro.

The first three locations in downtown Boston are within 8 to 10 miles of the WKLB transmission facility in Needham, Mass. They are the Greater Media studio building, a low-rise, two-story structure built with masonry, steel and glass; The Caning Shop, a single-story building of wood and masonry construction; and the Prudential Tower, a high-rise skyscraper of steel, aluminum and glass construction.

The other points where measurements were taken were farther out in the Boston Metro. They are a two-story, split-level home in Andover, of wood frame construction; the Comrex Corp. headquarters, a two-story steel framed, wood building in Devens; and a three-story apartment building of poured concrete (with rebar) construction in North Attleboro. These locations are at approximately the edge of digital coverage assuming the currently authorized –20 dB power level.

Up to four receivers, operated with manufacturer supplied antennas, were used simultaneously in each location to characterize reception at various points within each building. Generally, the closer testers were to the core of each building, the worse the digital reception was. Digital power was increased in 2 dB steps from –20 dB to –10 dB until the radio solidly locked onto the digital signal.

Testers concluded that in many types of buildings, digital reception is "simply impossible" on IBOC table radios and "nonexistent" on the new class of portable receivers about to be introduced into the market. An interim power level increase may partially mitigate the problem in some fixed locations, they concluded, however only the full 10 dB increase will permit reliable service to portable IBOC receivers and come close to replicating analog coverage.

As I noted, it's striking for advocates of HD Radio to state publicly that "digital reception is simply impossible in many types of buildings" and this says a lot about the HD Radio rollout. In pushing for an increase, the proponents are reiterating that they intentionally asked for a certain power level to be low enough so as not to cause analog interference to those stations nearby as well as those not yet digital. Engineers have said to me recently concerning the power issue that the NRSC, a largely volunteer effort, did what testing it could given the time and resources it had.