Digital Radio Rocking The Waves (Aug 15, 2005)

Fortunately for the DXers, it isn't widespread yet, but it is catching on.

KOGO 600 and KGB 101.5 have turned on their digital signals for radios equipped with decoding digital signals using the in-band-on-channel (IBOC) approach. Such radios are common as HD radios, which is not widely available in this area yet, though it's possible that Tweeters might soon be hawking them on their radio ads sometime soon.

KPBS-FM 89.5 (possibly as well as its La Jolla translator on 89.1 FM) plans to launch their digital signal by the end of the year. No word if they plan to convert their Calexico translator on 97.7 FM to digital as well.

Some say that it's like having subscription satellite radio for free, but so far, it's far from the 120 channel selection available for a fee from either XM or Sirius.

The positives of using digital signals are better sound for both the AM and FM radio stations. For just the FM stations, the capability of multiple signals, up to eight extra side signals, or channels, that can be broadcast alongside the main digital and analog radio channel using the same frequency applies to that band. This is called multicasting.

Multicasting isn't currently available for AM but the limitations of the 10kHz bandwidth for an AM signal (595 to 605kHz for KOGO's 5kHz on both sides of the main carrier footprint) are being worked on according to billboard.com. FM's bandwidth by comparison is 200kHz (or 0.2 MHz) for a station such as KGB-FM (101.40 MHz to 101.60 MHz) so four multicasted digital channels can be placed on each side of the main carrier signals (analog and digital).

FM stations for now can use the RDS (Radio Data Systems) digital method that sends special hidden messages (inaudible) to the HD receiver such as song titles, station IDs (a long needed feature), as well as emergency weather warnings. No word when and if this system will be available for AM radio. It's possible that it could help you tape music and talk shows while you're away and play them once you're in your car to hear them, kind of like TiVo's technology.

Although the fidelity for digital signals is decreased noise and the elimination of the hiss, as well as the elimination of electrical static (for the AM band such as those from motors and power lines), the tradeoff is the spillover of the digital signal to adjacent frequencies on both sides of the main frequency, so fans of 101.3 in Hemet and 101.7 in San Bernadino or Santa Barbara will be hissed out if they are too close to the transmitter of KGB-FM 101.5 near highway 94 near Lemon Grove.

I suppose digital radios can be engineered to tune out 101.5's digital overload on the adjacent frequencies, but I haven't come across any radio on the Internet that explicitly has that kind of selectivity.

What does the adjacent-channel interference sound like? On 590 and 610 kHz, the adjacent frequencies of KOGO, it would be something like that of a dial-up modem connecting to the Internet, something that's going to be history when broadbands' always-on featutre puts the last dial-up ISP out of business except for niche purposes like Internet faxing and e-mail. Some AM radios with not so good alternate channel selectivity can receive some weird ringing sound on 580 and 620 kHz in relation to KOGO. One upside to that is that KOGO's digital signal, like other digital AM stations, have to have its digital signal off at night, leaving only the regular analog signal on, due to potential long-distance interference, especially for the digital signals spilling over to the adjacent and alternate frequencies that could spell problems for stations up to about 1000 miles away at night, though it's unlikely that digital could travel that far.

On the FM band, here's what it sounds like: "ssssssssssssssssssssssssssssss". Just white noise with some analong sound spillover in it. It's like that of a blank cassette in a stereo tuned up to full blast. It's caused by the digital portion of the signal of, say KGB, spilling over to the adjacent frequencies of 101.3 and 101.7 MHz.

Co-channel interference from AM and FM stations work differently. On the AM side, if two stations are broadcasting on the same channel, they blend in, which is why you often hear Mariarchi music from XEROK 800 near the Texas border coming in at night to blend in with XESPN 800 in Tijuana. On the FM side, one triumphs over the other. In the case of digital interference, it will blend in with the distant AM stations, but blank out the FM stations, period. It's like a bad pirate radio station transmitter stepping over three frequencies at once. It's all caused by the IBOC digital approach to broadcasting.

The few ten thousand or so HD radio owners are enjoying some of the newer digital IBOC offerings that are being multicast with the second and third digital channels of the main station in some cities such as Miami and Chicago to name two cities, but as the prices of HD radios drop, expect to see more people buy the radios, leading to radio stations lauching more multicast digital signals with up to eight extra digital side channels per station, in the same way as digital TV is multicasting up to six digital channels for HDTV owners.

None of the San Diego-based radio stations are multicasting for now, but one radio station that could theoritically be multicasting is KPBS-FM, which could, say, launch classical on KPBS-FM-2, additional National Public Radio network offerings on KPBS-FM-3 featuring eclectic music or additional news programming such as BBC News, local public radio (or music you never hear on commercial radio such as college radio) on KPBS-FM-4, and even KPBS's main news/talk format completely in Spanish on KPBS-FM-5, and still have three channels left for more public radio offerings from network or local, or even a local weather channel.

Each radio station's multicasted channel can have a format that's related to that of the main channel, or something different. They can add in new formats to serve the underserved niche listeners that can afford to shell out the big bucks for HD radio receivers, the same kind of listeners that are familiar with and/or are paying for satellite radio.

No other stations plan to launch digital signals or multicasts this year, but there could be up to seven more players in 2006.

There is no conversion deadline for analog radio stations to convert to digital, but at this rate, I won't live to see the end of the day when analog radios will be able to pick up the analog-based signals. When that happens, the main digital channel (the one that repeats the analog signal on the main carrier frequency) can be moved into the main carrier frequency once the analog signal is retired, then power for the digial signal can be increased.