Re: Anyone notice that WLS has had the IBOC off this week?

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: : What's a IBOC? : In-band on-channel. : In-band on-channel (IBOC) is a method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. : By utilizing additional digital subcarriers or sidebands, digital information is "piggybacked" on a normal AM or FM analog signal, thus avoiding any complicated extra frequency allocation issues. However, by putting extra RF energy beyond the edge of the station's normally-defined channel, interference with adjacent channel stations is increased when using digital sidebands. : IBOC does allow for multiple program channels, though this can entail taking some existing subcarriers off the air to make additional bandwidth available in the modulation baseband. On FM, this could eventually mean removing stereo. On AM, IBOC is generally incompatible with analog stereo at all, and any additional channels are limited to highly-compressed voice, such as traffic and weather. Eventually, stations can go from hybrid mode (both analog and digital) to all-digital, by eliminating the baseband monophonic audio. : : AM methods: : HD Radio Broadcasting : iBiquity also created a mediumwave HD Radio system for AM, which is the only system approved by the Federal Communications Commission for digital AM broadcasting in the United States. The HD Radio system employs use of injecting digital sidebands above and below the audible portion of the analog audio on the primary carrier. This system also phase modulates the carrier in quadrature and injects more digital information on this phase-modulated portion of the carrier. It is based on the principle of AM stereo where it puts a digital signal where the C-QUAM system would put the analog stereo decoding information. : DRM : Digital Radio Mondiale has had much more success[citation needed] in creating an AM system, and one that could be much less expensive to implement than any proprietary HD Radio system, although it requires new frequency. It is the only one to have been accepted mediumwave but also shortwave (and possibly longwave) by the International Telecommunication Union (ITU) for use in regions I and III, but not yet in region II, the Americas. The HD Radio system has also been approved by International Telecommunication Union. : CAM-D : CAM-D is yet another method, though it is more of an extension of the current system. Developed by AM stereo pioneer Leonard Kahn, It encodes the treble on very small digital sidebands which do not cause interference to adjacent channels, and mixes it back with the analog baseband. Unlike the other two, it is not intended to be capable of multichannel, opting for quality over quantity. Unlike the HD system iBiquity calls "hybrid digital" the CAM-D system truly is a direct hybrid of both analog and digital. Some engineers believe that CAM-D may be compatible with analog AM stereo with the right engineering. : Critics of CAM-D point to several drawbacks: (a), being primarily analog, the system will be just as subject to artificial interference and noise as the current AM system; (b), there are virtually no receivers available for the system and at present, no major manufacturer has announced even the intention to begin production of them; and (c), the cost of retrofitting with CAM-D is more than that of simply buying a new, HD-ready solid state transmitter.

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