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.
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Copyright © 2005 Richard Wagoner and The Copley Press.
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