All-Digital AM-HD Tests Underway

Proponents of revitalizing the AM band using HD Radio are now testing the all-digital signal in the wild.
The guinea-pig is WBCN 1660 – a CBS-owned station in Charlotte, North Carolina. Currently a satellite-fed conservative talk station, WBCN will switch to a satellite-fed sports talk format in the new year. In a market of some two dozen stations, WBCN ranks 20th.
Sited on the expanded AM band (which happens to be the least-populated part of the AM dial), WBCN broadcasts with 10,000 watts during the day and 1,000 at night. The all-digital tests use the station’s analog power levels.
On October 18, CBS Radio filed a request for experimental authorization with the FCC to broadcast in full-digital AM-HD mode; this was granted on October 24, and it expires on February 3. CBS told the FCC it expects these tests “will be of significant value to the broadcast industry in demonstrating a possible solution to the delivery of the AM broadcasts in the presence of an ever increasing noise floor.”
According to listener reports, WBCN has been periodically testing the all-digital mode, mostly on the weekends when its listenership is lowest. The last known test occurred on Sunday, December 9.
The choice of station makes sense: low ratings and a generally small broadcast area mean the chances of interference or listener disruption are minimized. Incidentally, all-digital AM-HD signals occupy a smaller footprint on the dial (20 kilohertz) than hybrid analog/digital broadcasts do (30 kilohertz), though both are still fatter than an analog AM footprint (10 kilohertz).
Without any knowledge of the testing protocols, it’s impossible to evaluate just how significant the value of the results will be. Conducting these tests on WBCN represents a best-case scenario for the all-digital AM-HD protocol. Hopefully, such testing will involve multiple stations in multiple markets under varied conditions (different license classes, transmitter/antenna array combinations, ground conduction conditions, etc.)
However, if the plan to digitize the AM band evolves like the implementation of HD itself did, it will be based a relative pittance of technical data, collected in secret and immune from peer review. These tests on WBCN may be the only one (or two) of its kind before proponents take the next step of asking the FCC to authorize all-digital AM-HD broadcasts for real and full-time.
The implications of this move have yet to be discussed in any meaningful way among all constituencies involved in AM broadcasting, including the public’s perspective. The opacity of the ongoing tests does not bode well for that discussion actually taking place before constitutive choices are made.