AM Modulation, Multiple Channels All Part of HD Radio World

Harris has developed its first AM transmitter specifically for HD Radio at lower power levels. Ky Luu spoke about advanced pulse duration modulation during the Broadcast Engineering session titled, “State of the Art of Radio.”
The idea behind the new transmitter is that Harris wanted to provide the same performance as the higher-power Harris DX transmitters, but make the product cost-effective for 1kW to 6 kW levels.
This is the first AM transmitter to use adaptive pre-correction of distortion around the entire transmitter system, Luu said.
NPR’s Mike Starling then detailed the results of the so-called “Tomorrow Radio” tests. NPR, Harris and Kenwood tested an FM digital split-channel concept at 4 stations over a 7 week period last summer. The four stations were: WYNC, New York; WETA, Washington; KALW, San Francisco and KKJZ, Los Angeles.
Starling said the tests proved that by splitting the 96 kbps FM digital channel into 64kpbs and 32kpbs channels, the test stations achieved good signal coverage up to their 60 dBu contour.
NPR is pleased the commission included questions about the split-channel concept in its Further Notice of Proposed Rule Making for IBOC issued April 15. The network is encouraged by comments on that Further Notice from Commissioners Jonathan Adelstein and Michael Copps that mentioned the potential public service benefits of the supplemental audio channel.