The experiment to see if an entire state can be covered by digital shortwave signals is slowly progressing, according to another NAB Show presentation.
Dr. Donald Messer, longtime shortwave broadcasting and Digital Radio Mondiale proponent, updated attendees about his plans to test DRM for an ambitious “local” shortwave service covering the state of Alaska.
Dr. Donald Messer discusses the Alaska DRM tests. Photo by Jim Peck
With more than half of Alaska’s population concentrated around Anchorage and a few other urbanized areas, and the remainder widely distributed over a half-million square mile land mass, the state is one of the most sparsely populated areas in the world. This creates a challenging environment for the economics of FM and AM broadcasting, even before the harsh weather and limited accessibility of transmitter sites are considered.
The result is that many people throughout the state have limited or nonexistent access to broadcast radio.
Messer said three surplus 100 kW transmitters have been obtained from the Department of Defense and are now being tested into dummy loads in an underground mine near Fairbanks, and the first of three crossed half-wave dipole antennas has been constructed.
The test plan includes a series of experiments to determine what frequency bands and power levels are needed to provide reliable year-round service, as well as which combination of RF bandwidth, error correction and QAM constellation size provides the best balance of throughput and signal robustness from the DRM system.
Of particular interest is the nature of ionospheric propagation at high latitudes; providing statewide broadcast service requires a consistent and predictable “bounce back” of signals from the ionosphere and understanding the behavior of these reflections will require extensive experimentation, Messer notes.
To assist in the analysis of reception variability, a network of 18 remote receive sites will be set up around Alaska’s periphery to feed reception data back to the project headquarters in Fairbanks. Messer expects construction of the transmission system and remote receivers to be completed later this year. After that, a two-year data collection and experimentation project is planned.
Messer seemed careful not to sound over-optimistic that the system would work.
(Radio World)
