Documents were filed with the agency late last week by HD Radio’s proprietor, iBiquity Digital Corporation, to allow FM-HD stations to increase the power of their digital sidebands by a factor of 10. The rationale behind this request is increasing field evidence which shows that the digital portion of FM-HD signals fails miserably at matching increasing analog signal coverage, and the existing power level does not allow digital signals to penetrate buildings very well.
This proposal does not come without risk; evidence of HD signals interfering with other stations is already well-known, especially on the AM side, and the Corporation for Public Broadcasting has completed a study that adds new information to the body of knowledge regarding FM-HD interference. Unfortunately, the results of this study have not yet been made public, though notably National Public Radio itself has not taken a position on whether or not increasing the digital output of FM stations is a good idea.
In the FM environment, increasing the power of digital sidebands contains two main risks: the first is increased interference to nearby stations on the FM dial, and the second is increased interference between the analog and digital signals of an HD-capable radio station.
Whereas a digital FM-HD signal broadcasts at just 1/100th the power of its parent analog station, the relative power differential of the potentially-interfering digital signal to adjacent stations is large enough that any interference is, for now, very localized and not very noticeable. Allowing stations to broadcast a digital signal at 1/10th the power of its analog counterpart is a very different matter.
For example, my community radio station, WEFT, typically broadcasts a 10,000-watt analog signal. Under current FCC rules, WEFT could broadcast a 100-watt digital signal in its sidebands. Under the proposed rule change, that digital signal’s power could be increased to 1,000 watts. You can’t get around the physics: if you increase output energy in the sidebands, you risk the potential to interfere at a greater magnitude to nearby stations. So far, this proposal to increase the FM-HD sideband power has only been tested in the lab, not the real world (sound familiar?).
Secondly, because the digital portion of an FM-HD signal, by design, encroaches on bandwidth reserved for analog broadcasting, increasing the power of the digital sidebands also contains the potential for increased interference between a station’s analog and digital signals. This typically manifests itself as a “hissing noise” or “grunge” heard when listening to an FM-HD station’s analog signal. Again, there is no real-world evidence to suggest that this potential parasitic interference will not increase if FM stations raise their digital sideband power levels.
Why would radio stations would take the risk of degrading the quality of their existing analog service in order to pimp a flawed technology which nobody’s listening to? It’s almost as if the strategy of the HD Radio Alliance is to degrade analog radio service in order to force digital adoption – kind of a variant on the “we had to destroy the village to save it” rationale.
Even though it supports this proposal, the National Association of Broadcasters is candid enough to admit that raising the power of FM-HD sidebands “may create new instances of interference in certain situations.” In the same breath, however, the NAB says it’s confident that the already-overworked FCC Enforcement Bureau can handle new interference complaints on a case-by-case basis as they arise, and concludes that “the benefits to be gained for FM broadcasters and FM listeners will far outweigh the limited additional interference predicted by iBiquity’s studies.”
It’s anyone’s guess as to when the FCC will consider this proposal, but if the history of the entire HD Radio rulemaking is any indication, the power increase will be rubber-stamped, and we will suffer the consequences as they unfold.
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