Washington - Aug 2, 2011 - With funding from the NAB Fastroad Technology Advocacy Program, iBiquity constructed and tested two FM band digital radio Single Frequency Networks (SFNs) and has now published a report of the results.
The first SFN was built in the Baltimore area and consisted of experimental stations WD2XAB and WD2XAB-FM1. The second SFN was constructed and tested with the assistance of Greater Media Boston, and consisted of an SFN booster site in Andover, MA, (WKLB-FM1) to supplement the WKLB-FM main site in Needham, MA.
The report characterizes the following:
Digital performance, main site alone
Digital performance, booster site alone
Digital performance, main and booster sites together
Digital-only booster interference to main analog carrier (near booster transmitter)
Hybrid booster analog carrier interference to main analog carrier
The report concludes that HD Radio SFNs provide broadcasters with the ability to selectively extend digital coverage within their protected contour without compromising the existing HD Radio digital service area. More specifically, the results showed that, in operating an SFN, digital time delays between main and booster signals need to be adjusted to account for propagation delays in the overlap regions to minimize inter-symbol interference. Two over-lapping, properly aligned and synchronized, digital signals do not degrade HD Radio performance; instead, digital coverage is enhanced within the station's protected contour when using a SFN with a digital-only booster.
The Boston tests actually used real-world receivers for a subjective listening test. It was concluded that a modern receiver design (such as a recent model Delphi) experienced little interference to the main station's host analog signal near an all-digital booster station. Unfortunately older receivers (in this case, an older Chrysler automotive receiver) did not respond well in near proximity to the digital-only booster, and became unusable when too close to the digital-only booster transmitter. A run-of-the-mill clock radio also did not perform well in close proximity to the digital-only transmitter.