HD Radio Boston Area
Fri Oct 13 13:26:41 EDT 2006
Ken, the tongue-in-cheek reason is that radio stations have been lying
to you for over 50 years. :-)
By which I mean that the "problem" with IBOC (the actual generic term
for this kind of digital radio..."HD Radio" is a brand name) is that it
only reaches as far as the FM station's protected contour. In most
cases, this is MUCH smaller than many people are used to because an
analog signal is usually listenable well beyond the protected
contour...in some cases 50 to 200% as far away.
The tradeoff here is that digital maintains the same quality of service
(QoS) right up until the point where the digital signal hits the cutoff
threshold. So in an area where an analog signal might have only 75% of
good "audio quality/fidelity", and a car radio might be blending to mono
or suffering from multipath...the digital signal will sound exactly as
good as it would standing next to the transmitter. No fades, no
static, no clicks or pops, etc.
The problem, of course, is that many stations are "losing" a severe
number of their fringe listeners. Listeners the FCC has told them for
years that they cannot count on but the stations did anyway. It's a
paradigm shift in the concept of "listening to radio" and it will not be
an easy transition for stations or listeners.
Now, that all said, Chelmsford is certainly within the protected contour
of several IBOC-equipped stations you're probably trying to listen to
(like the biggies on the Pru, for example). So why are you having
trouble getting a clean HD signal?
First, the quality of the receivers has been spotty at best. Too much
focus on just getting the damn things out to market because they've been
delayed so much...not enough focus on making sure they can actually get
an AM or FM signal! I've got a long rant on this issue that I'll
dispense with for now...but I'd like to hope that this particular aspect
will dramatically improve as more IBOC radios hit the market this year
Second, given that this is a VERY new technology when you're talking
about the actual hardware installed at various sites...there are a host
of stations that have their IBOC installations "wrong". I emphasize the
quotes there because no one's entirely sure how to do it "right" quite
yet. For all the testing and engineering, you never really quite know
how a system is going to behave until you get it out in the field.
There are a host of stories I've heard of entirely unheard-of problems
suddenly popping up once an IBOC system was added. Or sometimes systems
(often antennas) that had minor problems; problems not big enough to
affect the analog-only system but when you toss in IBOC things start to
It's not anyone's fault. Again: IT'S NOT ANYONE'S FAULT. Lots of this
stuff is all but impossible (or fiscally not feasible) to anticipate
before you actually go out and do it. But the world (and many tower
sites) are awash in wireless communications systems these days and they
all interact with each other in strange and wondrous ways.
A great example is the Pru - try listening to each Pru station's IBOC
signal and you'll notice that not all them "come in" as good. Which
shouldn't be the case...they all use the same damn antenna! So why's
that difference there? Who knows?!? Could be atmospherics. Could be a
flaw in the master antenna. Could be some form of intermod. Could be
problems with the combiner. Or the individual transmitters. Or the
encoders. Tracking down problems like this is often maddening and
Never forget that while the digital signal is far more "robust" than the
analog...it's still 100 times (-20dB) weaker than the analog.
Interference and interactions the 22000 watts ERP would laugh at could
severely affect a 220 watt ERP digital signal. Especially at a distance
of 30 miles!
All that said, I would anticipate that as time goes on you will see IBOC
reception improving as systems are tweaked and better radios hit the market.
It is unfortunate that so many sub-standard radios are on the market
right now since (by and large) only us radio geeks are buying them.
We're the ones our non-radio-geek friends are asking whether or not THEY
should be buying into the HD Radio concept and the honest answer (too
often) is "not yet". Or worse, "don't bother/forget about it". This
bodes ill, to put it mildly, for a concept that can ultimately bring a
lot of benefit to radio as time goes on.
Boston, MA 02246
Fried Bagels - Broadcast Radio & Web
Engineering & Operations Consultant
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