HD Radio Boston Area

Aaron Read readaaron@friedbagels.com
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 
and next.

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 
go wrong.

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 
usually time-consuming.

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.


Aaron Read
Boston, MA 02246

Fried Bagels - Broadcast Radio & Web
Engineering & Operations Consultant

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