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FM Coverage Area

This is one in a series in which Ibiquity Digital Corp. answers questions about how to implement in-band, on-channel digital audio broadcasting. Broadcast Technology Manager Jeff Detweiler answers here.

This is one in a series in which Ibiquity Digital Corp. answers questions about how to implement in-band, on-channel digital audio broadcasting. Broadcast Technology Manager Jeff Detweiler answers here.

Q: Will IBOC improve the signal coverage of my FM stations?

A: FM IBOC offers improvements in signal reception and audio quality, and it can improve signal coverage in some markets.

Although the system is not designed to extend the coverage area farther from the transmitter, the IBOC system’s ability to overcome impairments such as multipath will allow many broadcasters to reach listeners that are unable to receive existing analog signals.

These IBOC characteristics have the ability to significantly enhance the listener’s experience, a conclusion recently reached by the National Radio Systems Committee in its report to the FCC on FM IBOC.

The level of the IBOC digital carriers and the transmitting antenna’s height above average terrain determines how far a station’s FM IBOC signal will travel. With the IBOC carriers set at 20 dB below the analog carrier, the proposed level for hybrid mode operation, IBOC digital coverage is comparable to analog.

In the NRSC’s report to the FCC, the test evaluators stated, “FM IBOC service might be obtained in areas where analog service is presently unacceptable due to interference.” This improvement is due to IBOC’s signal robustness.

NRSC test results confirm that the Ibiquity FM IBOC system, compared to analog FM, is substantially more robust. The digital signal survives when faced with interference from impulse noise, co-channel and adjacent channel, as well as multipath fading.

IBOC cannot overcome the strong interference that exists beyond the edge of coverage, nor was it designed to. Coverage radius will not increase, but the usable service area within the existing service contour will increase.

The FM IBOC system has also demonstrated significantly improved audio quality compared to existing analog FM, especially in mobile listening environments. This will further enhance the listening experience in the existing coverage area.

The NRSC recommendation to the FCC summarized the FM coverage issue best:

“The NRSC believes that the Ibiquity FM IBOC system as tested will offer FM broadcasters significantly enhanced performance over that which is presently available from traditional analog FM broadcasting.

“The enhancements include almost full immunity from typical FM multipath reception problems, significantly improved full-stereo coverage, flexible datacasting opportunities and an efficient means for FM broadcasters to begin the transition to digital broadcasting.”

Send your IBOC questions for a reply in this space. E-mail toradioworld@imaspub.com.

Radio World welcomes other points of view.

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