Radio listeners across America are trying to hide from a monster, but there is no shelter. After spending its adolescence in technical trials during daytime hours, IBOC has now come out at night. IBOC is the acronym for in-band on-channel, a method of sending digital audio along with old-fashioned analog radio signals. It's marketed, confusingly, as HD Radio. In theory, HD Radio should be transparent to the end user listener. In reality, the system is anything but on-channel. It actually uses about five channels to convey its information.
For example, in New York City, WOR broadcasts on 710 kilohertz. When it turns on its IBOC equipment, the digital noise it produces can be heard on 690, 700, 720 and 730 kilohertz with a reduced fidelity analog audio signal remaining on 710. During the daytime, AM radio signals only travel, at best, 100 miles, so the effects of IBOC's digital noise are somewhat contained. At night, AM radio signals can been heard long distances from their origin. With thousands of AM stations broadcasting simultaneously every night, the result is a chaotic soup. Now add wideband digital noise via IBOC. Only the very strongest signals can survive to provide useful reception.
Adding to this problem, the receivers that can decode HD Radio require a very potent signal to resolve digital audio. The end result can be digital audio delivered via the AM band, but it is only available to a limited audience with close proximity to the broadcaster. So many of us hear the noise, but so few of us can hear the intended clear signals! It sounds like a thousand bees relentlessly heading in your direction!
The signature of AM radio has always been highly reliable and resilient long distance communications. With the advent of HD Radio, AM has been scaled back to a local medium with limited distribution. Shows that enjoyed nearly nationwide coverage, like WSM Nashville's Grand Ole Opry, are being shattered by all the new interference produced by the wideband nature of HD Radio.
HD Radio broadcasters are also in conflict with themselves. CBS owns both KDKA 1020 Pittsburgh and WBZ 1030 Boston. AM radio DXers have noticed that both stations have only been operating their HD Radio equipment irregularly at night trying to reach a compromise to keep both station's coverage area whole. We have met the enemy and he is us! The effects of HD Radio interference may be the final death blow to struggling small local radio stations trying to compete in very difficult market situations. This noisy hash may extinguish all hope of local stations being heard in the clear ever again.
A similar IBOC system is being used on the FM band. FM allows for more bandwidth allowing IBOC stations to broadcast more than one audio source on their frequency. Noise to neighboring channels is similar, but the relative short range of FM contains the melee. The FM version of HD Radio also requires a very strong signal to be decoded. Reception can be finicky in nature. These signals need to be received perfectly to provide the intended results to the consumer.
HD Radio may be a short term band-aid for aging over-the-air technology. Multi-channel digital satellite radio and WiFi delivered radio and television will probably be the standards for the future. Large conglomerate broadcasters, who own hundreds or thousands of stations, are desperate to counteract the onslaught of competition from the Internet, iPods and various other methods of streaming. It seems ironic that the industry that insisted on narrowing the fidelity of AM radio to 10 kilohertz over a decade ago to clean up adjacent channel interference now allows 30 kilohertz or more bandwidth to compete with other digital media!
AM DXers are hoping that two strategies may help silence nighttime HD Radio. The rallying cry has already begun to complain directly to the FCC and the offending broadcasters about the reduced coverage and noise that HD Radio brings. Possibly more significantly, our neighbors in Canada and Mexico are not yet participating in HD Radio or endorsing its use. The deluge of interference American HD broadcasts inflict on their signals may create quite a dilemma that can only be solved by silencing HD's use at night. Time will tell! If you notice new broadband noise on AM radio, you are probably listening to the sound of 'progress!' Stay tuned, (if you can stand it!) Even better, hear it for yourself at: http://www.wysl1040.com/media_files/wysl/IBOC_OBSERVATIONS.mp3