Since my run-in at the NAB Radio Show with industry forces spearheading experimentation with the all-digital AM variant of HD Radio, they have been busy. Back in September, testing was underway on stations in Seattle—the eighth and ninth such stations to conduct tests in the last two years—and the NAB et al. described the preliminary results as quite positive.

When the tests concluded in October, the president of the stations hosting them in Seattle said that while the experience was good, some listeners wondered if their stations would be going all-digital anytime soon. Not for at least 10 years, replied the executive, “because regulatory efforts take time.”

Last month, David Layer, the NAB’s senior director of advanced engineering, told a conference that during the daytime, the all-digital AM-HD signal outperformed both the hybrid analog/digital and analog-only AM signals on the test-stations. At night, however, the all-digital signal was less robust and the analog signal still had the largest reach: “It wasn’t great, but you could definitely listen to it. If you were listening a ball game or something you cared about, you’d probably stay tuned in,” said Layer. “I think one of the dilemmas for the industry is what to do about night. Daytime coverage is pretty phenomenal, but nighttime coverage — depending on the frequency — can be a lot more limited.”

Layer also said that the relative improvements seen with all-digital AM are contingent on local interference conditions, especially where there are stations on adjacent channels to each other, and this is an issue that remains under study. Although the all-digital AM-HD signal occupies twice the spectrum of a plain old analog AM signal (smaller than the 3x footprint of hybrid analog/digital AM), it’s still an expansion of the use of the AM spectrum, with obvious potential consequences.

Thus, much like its hybrid analog/digital cousin, all-digital AM-HD would seem to be a partial solution to the technological ills of AM broadcasting. If the history of hybrid AM-HD is any indication, the vast majority of broadcasters will be unwilling to embrace another half-measure.

This is not stopping HD proponents from prepping the regulatory ground for FCC authorization of all-digital AM, perhaps by as early as next year. On October 28, Clear Channel’s iHeart Communications’ chief engineering executive held a series of private meetings with key advisors to every Commissioner and the Media Bureau. With regard to all-digital AM-HD, Clear Channel iHeart says that while it shows promise, it deserves further study, especially since “less than three percent of radios are equipped with HD digital receivers.” The takeaway: “while iHeart continues to support the grant of all-digital authority for AM stations on an experimental basis, it would be premature for the broad implementation of all-digital authority.”

This was followed on November 5 by a conversation between the National Association of Black Owned Broadcasters and an adviser to FCC Chairman Tom Wheeler, in which NABOB expressed support for “allowing [station] licensees to choose all-digital transmission” with nothing more than a letter of notification to the FCC. Then, on November 14, the NAB had a meeting with a policy advisor to Commissioner Jessica Rosenworcel, during which it advocated for “[m]odifying the Commission’s rules to effectuate technical and policy changes [that] will enhance AM signal quality and promote the continued viability of AM radio broadcasting.”

It’s pretty clear by this point that the National Assocation of Broadcasters is directly carrying the ball with regard to advancing HD Radio in the policy domain; it has always been a powerful and strategic partner among HD proponents but now it’s a task to which iBqiuity Digital Corporation and individual broadcast conglomerates play supportive roles. Several proposals, such as giving AM stations one last run at freebie FM translators and relaxing a bevy of engineering requirements for AM transmission, are all but guaranteed. But the harder questions, like eliminating sources of AM interference generated by consumer electronics and just what AM’s digital future may portend, are still up for grabs.

The extremely preliminary information meted out by HD proponents already seems to suggest that the all-digital AM signal is susceptible to many of the same limitations as the interim hybrid variant—primarily interference, both in transmission and reception, which is especially exacerbated at night. It’s important to remember that AM-HD’s first launch was stunted by both fidelity and interference problems, so much so that the industry and FCC had really no choice but to start with interim authorization during the daytime only. At present, 56 of the 168 AM-HD stations on the air in the U.S. are digital at night. Among AM stations in total, just 3% of have adopted HD in any configuration and only 1.2% use it 24/7.

Even though such stations demonstrably generate interference, it is apparently as tolerable as the sort of interference that already plagues the AM band. AM-HD broadcasters may still soil their adjacent channels, but it stinks less than the noise generated by your neighbor’s big-screen TV and outdoor lighting.

Thus the ask for AM-HD in any upcoming concrete policy initiative will be limited: voluntary and during the daytime only. The big question, as Clear Channel iHeart delicately put it, will be whether AM broadcasters are willing to gamble alienating their analog audience for this version of radio’s digital future. One of them, Disney, has already decided against it, selling all but one of its AM stations in a transition to primarily online content distribution, because that’s where the kids are. Incidentally, Radio Disney was a prime mover for AM-HD: iBiquity’s own list shows 17 AM-HD Radio Disney stations, representing 11% of installed base of AM-HD broadcasters. It’s anyone’s guess whether those stations will keep their commitment to digital broadcasting.