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Radio AM to FM: June 3, 2005

Digital Radio Claims Two More

The conversion of traditional radio stations to digital using an in-band-on-channel approach continues in spite of the problems it causes to millions of analog radio sets currently in use. Over 99.9 percent of radios are analog, due primarily to the fact that digital, or HD radios, are not even available in much of the country.

The upside to digital is the promise of better sound for both AM and FM and the capability of split signals -- multiple formats using the same frequency -- on FM. Stations on both bands can also use a digital version of RDS -- Radio Data Systems -- that sends messages to the receiver and is currently available only for FM. Such messages may include song titles, stations identification or even storm or traffic warnings.

Decreased noise and no hiss are the hallmarks of digital, and as a subscriber to Sirius satellite radio, I can attest to the freedom from noise on a digital carrier.

The downside is increased analog interference. The interference on AM is a modem-like hash sound just like the sound you hear when you use dial-up internet on your computer. The noise completely drowns out any first-adjacent channels you may have formerly been able to hear, and it causes a distinct ringing sound on the second-adjacent channels even if you can still hear them. Currently digital radio cannot be used on AM at night due to potential long-distance interference.

On FM, the interference is a bit more sinister. You won't hear the actual noise on an adjacent station as you would AM, but the digital portion of the signal extends further into the next frequency than the analog signal and "fools" the receiver into thinking that listenable audio is there. The net effect is that weak or distant stations you could hear in the past are poof! Gone. Nothing. You might think it's the weather, but it's IBOC digital.

Another downside is vastly decreased range of the digital signal compared with analog. For example, using analog I can hear any number of AM or FM stations from San Diego or Santa Barbara from my house. At night, AM stations have come in from as far as Minneapolis. Digital, due to it's all or nothing behavior, will not travel that far.

At least until (if ever) analog is turned off. Once the system is no longer a hybrid but instead 100% digital, the digital carriers can be moved closer to the main carrier (frequency) and digital power can be increased. Problem is, all those millions of radios that no longer work.

At any rate, you can add two more stations to the local digital "HD Radio" stable. KNX has been operating digitally full-time for a few weeks, while KDIS is expected to make the move by the end of this month. Hopefully, I'll be able to watch the conversion in person. Once I hear it for myself, I may become a convert. I do have to admit, though: currently I am skeptical.

One thing about it, though. Maybe with digital, music will come back to AM and we'll have some real choices again.


Copyright © 2005 Richard Wagoner and The Copley Press.

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