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[IRCA] IBOC comments
Forwarded from Barry M.
-------------------
A few thoughts as nighttime IBOC operation looms later this week...
Digital transmission has some advantages, but the hybrid digital system
is a lousy fit for the AM band. Aside from the cost of conversion for
the broadcasters, there are indirect costs associated with damage to
analog services, both for the IBOC players and for those staying on the
sidelines. The broadcasters have never had a clear idea of these
indirect costs, since iBiquity, the NAB, and other IBOC proponents have
always downplayed the problems. Now the rubber starts to hit the road,
and to understand what they've gotten into, the broadcasters need to get
feedback from their audience... lots of it. Come 9/14, let the
interference complaints flow, but keep a few things in mind:
It should be obvious, but it bears repeating: you are reporting
interference in the context of being a radio listener, not a DX'er.
Keep it polite and to the point, and omit the anti-IBOC diatribes.
Complaints should go to the station being interfered with, not the
station(s) causing the interference. There are a few exceptions,
however. If you feel that an IBOC station's own digital emissions have
degraded their analog signal quality, you should let them know. Or, if
you have reason to believe that their IBOC equipment is malfunctioning,
you should contact them, but make sure you're on firm ground before you
do so.
Keep in mind that interference complaints are more likely to be taken
seriously if they affect reception in or near protected contours. The
first question to ask yourself is whether the reception is by skywave or
groundwave. Only the Class A stations on the "clear" channels have
protected skywave service, so complaints about interference to skywave
signals will likely fall on deaf ears unless one of those stations is on
the receiving end of the interference. If in doubt, you can check a
station's class using sites such as fccinfo.com or radio-locator.com.
Of course, some of the large market Class A's have little or no interest
in skywave service, WOR being a prime example. At the other end of the
spectrum are stations such as WSM that still have big skywave audiences,
and thus should be more receptive to interference reports.
Some folks argue that AM skywave service is going the way of the dodo
anyway. Perhaps they're right, but IBOC definitely does not just affect
skywave reception. We all need to take a close look at IBOC
interference to our local and semi-local stations that are receivable by
groundwave at night. The difficulty here is to assess whether your
location is in a station's nighttime protected contour, which is defined
by something called the Nighttime Interference Free (NIF) contour.
NIF contours are based upon calculations, but unfortunately, they are
not generally documented anywhere that is accessible to the general
public, nor is there any free software available to do the calculations.
My advice: don't worry about this arcane stuff. If you get normally
get good groundwave reception of a station at night, and it becomes
significantly degraded after nighttime IBOC starts, then you should
report it to them. Let them decide whether your reception problems
merit any action on their part.
If you want to get a very rough idea of a station's nighttime groundwave
coverage, you can try looking it up on the radio-locator site. The red
contour line is an approximation of the 2.5 mV/m contour. Except for
the Class A stations, most stations will have a NIF contour that is
somewhat smaller than this (in some cases, a LOT smaller). But don't
get too hung up on the contours at this point... if you had decent
reception before IBOC, and it goes seriously downhill after nighttime
IBOC starts, then it's worthwhile reporting it.
Remember also that a recording could be worth a thousand words. A short
audio clip of the interference could be a valuable addendum to your
interference report. If you're keen, and have some inkling of which
local stations might be interfered with, it would be worthwhile to make
some recordings this week, so that you have some "before" and "after"
comparisons available. The stations themselves should be doing this,
but I doubt that many will!
Lastly, it should be noted that not all of the current AM IBOC stations
(223 at last count) will begin 24/7 IBOC operation on Sept. 14. Some
will have issues to sort out with automation, bandwidth of their night
array, and so forth (and some of them, fortunately, are daytimers :-).
The stations that do not have to change facilities at night are the most
likely to keep it rolling through the night on 9/14. So, it will be
important to keep track of which stations are actually running it at
night, and to that end, I've added a column to the table on my AM IBOC page
(http://topazdesigns.com/iboc/station-list.html) to show nighttime status.
I encourage everyone to report the status of the IBOC stations they can
hear, either on these lists or, if you prefer, directly to me.
Let the beta test begin!
Barry
-- Barry Mc Larnon VE3JF Ottawa, ON
--
Bill Harms
Elkridge, Maryland
Check out the Spokane Radio History Pages
http://spokaneradio.philcobill.com
and the Spokane Radio Tower Pages
http://spokanetowers.philcobill.com
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