HD-R proponents who want the FCC to approve a voluntary increase in digital power of up to 10 dB hope the commission won’t take a long time to reach that decision once the request is formalized.
A 10 dB increase is a 10 times increase in digital power, according to engineering sources. “This is like 60 kW instead of 6 kW in the analog world,” said one.
Existing FM stations transmitting both a digital and analog signal are required to set the IBOC power level 20 dB below the analog power level.
Some 13 stations already have approval of sorts in the form of experimental authorizations to test the concept in two parts. CBS Radio, Greater Media and Clear Channel Radio participated in that testing.
The material also discusses related coverage tests conducted by NPR Labs, which, John Kean told me at the time, were to find out where the digital signal is going, and where it’s not.
The first part of the testing, conducted by Ibiquity and signed off on by Hammett & Edison, looked at the digital coverage increase at the higher power level; comparing digital coverage at 20 dB below analog power and 10 dB below analog power level.
Tests occurred September in three geographic areas with different terrain characteristics: the New York, Connecticut and Rhode Island region; Detroit; and Los Angeles, San Diego and Santa Barbara.
In all cases, according to documentation I saw that fell over my transom window, the increased digital power level “significantly improved” digital coverage — like 26% in Connecticut and 33% increase in the distance covered by the digital signal in Detroit.
Even with increased digital power levels, the FCC spectrum mask would still be maintained, according to the results.
Results reportedly show the higher power level would not cause “unacceptable interference” in most circumstances, even outside a station’s protected contour. This point certainly sounds debatable.
However, questions remain, such as how to handle short-spaced and super-powered FMs and stations that use directional antennas. Some proponents believe these situations could be handled on a case-by-case basis.
Some stations don’t have the headroom needed to implement the power increase in their transmitters, sources said, while other stations may potentially see self-interference due to more strict transmission system performance requirements. Another potential shortfall is potentially increased interference to first-adjacent channel analog listeners.
My bet is, when this proposal is turned in to the agency by NAB (and we don’t know yet when that will be), the commission will take a L-O-N-G time to vet this one in this election year.