Washington - May 7, 2013 - The recent AM IBOC-only test (MA3 mode) tests that were conducted with CBS radio station WBCN-AM were discussed in detail during the 2013 NAB Show. The results are of great interest to many, so here's a look at how they were derived.
The test used an all-digital transmission, which places the digital carriers in the center of the carrier channel. In the hybrid mode, the analog signal is placed in the center of the carrier with the digital information on either side.
According to NAB Tech Check: "Once the transmitter was properly calibrated for operation in MA3 mode, an iBiquity test vehicle was driven along each test route to establish the digital point of failure (POF). Principal determination of all-digital signal reception and POF was done using an OEM Ford Sync HD Radio receiver that was factory-installed in a Ford Focus automobile and connected to the vehicle's built-in antenna. A custom data interface to this receiver was designed by iBiquity utilizing the auto's "I2C" data bus allowing for connection to a laptop computer. Note that principal determination of all-digital signal reception was done using this receiver/antenna combination since this most accurately represents an actual consumer experience.
"Information collected on the laptop computer was obtained from the OEM receiver as well as a GPS receiver (connected via USB) and included time (UTC), position (latitude and longitude), vehicle speed, receive mode (all-digital enhanced, all-digital core, no reception), and RF signal-to-noise ratio (SNR). Software was custom-designed by iBiquity for AM HD Radio data collection.
"The typical experience on each test route was that all-digital reception would be solid, with no "drop-outs," in strong signal areas near the transmit antenna, and it would stay solid with only an occasional drop-out until near the all-digital POF, at which point reception would fairly abruptly become intermittent and then be lost completely. Reception data collected from the Ford Sync receiver is illustrated in the figure shown here for daytime reception. (Nighttime mobile results, and daytime and nighttime indoor results were obtained as well, and are contained in the full paper.)"
The results, placed on a coverage map, look very impressive.
Image reprinted by permission, from WBCN All-digital AM IBOC Field Test Project by David Layer et al as published in the NAB Broadcast Engineering Conference Proceedings 2013. Copyright 2013 National Association of Broadcasters.
The result to take notice of is that on all six test routes, the POF (point of failure of the IBOC reception) goes out very much past the 1mV/m contour of the station.
This paper is included in its entirety in the 2013 NAB BEC Proceedings, available online from the NAB Store.