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Re: [IRCA] A Perfect Example
- Subject: Re: [IRCA] A Perfect Example
- From: Scott Fybush <scott@xxxxxxxxxx>
- Date: Sun, 05 Mar 2006 17:52:50 -0500
Neil Kazaross wrote:
> 73 KAZ wanting you to truly understand how bad nighttime IBOC will be. The
> only ones of us who will be able to still get much decent DX during
> widespread nightime IBOC will be living in corner of the US and needing
> phasing and cardiod patterned antennas. ie..NEw England will still be OK for
> TA with a cardiod to take out most domestic QRM and will still be OK for
> LA's in deep AU's.
This strikes me as perhaps an overly pessimistic view of the matter.
First, I don't foresee a scenario where every AM station goes IBOC. Here
in my medium-sized market, out of nine in-market signals, three are IBOC
now (Crawford's 990 and CC's 1180 and 1280), one more has plans to go
IBOC (Entercom's 950), one has vague thoughts of doing it (public radio
1370), and the remaining four simply won't - they don't have the money,
they're not corporate-owned, and they don't see much of anything to gain
from making the flip.
That proportion will probably go a little higher in major markets, but
will certainly be even lower in smaller markets. So out of 5,000 or so
AM stations in the U.S., my guess is that we'll never see more than
perhaps 2,000 adopting IBOC.
It's theoretically possible, if someone had the software (I don't) and
the time (ditto), to come up with a pretty accurate list of what those
2,000 stations are likely to be, based on market size and group
ownership, and from that to generate some pretty accurate studies of
what the actual levels of interference generated will be.
But we don't need to go to that level of detail to get a pretty good
idea, because IBOC interference will largely track the existing BCB
noise levels that we as DXers know all too well.
On the (ex-)clear channels, the effect will be fairly ugly, I expect,
not only because the digital power levels will be fairly high but
because they'll be single-source interference generators on each
channel. AM engineers know that it's not just the level of interference
on a given frequency that can cause problems, it's the number of sources
generating that interference. For instance, the overall incoming signal
level here might be the same on 1020 from WBZ's analog sideband as it is
on 1400 from the forest of graveyarders, but the noise from that one
source is going to be far more annoying to listen to than the overall
murmur from all the graveyarders going at once. Same deal, to an extent,
with IBOC - it will most surely be a mess when WSB, WJR, WABC and WBBM
are all stepping on each other across the entire eastern seaboard every
night.
On the other hand, BECAUSE these are single sources of interference,
they're nullable. If KAZ can phase WGN's main carrier down enough to
hear KDWN 15 miles away from the transmitter, he'll just as surely be
able to phase the sideband hash down to hear KIRO or KBSU.
(The clears will probably be the best test of the difference between
casual listening and DX listening, and indeed will probably be the only
place most casual listeners will hear the effects of IBOC. The guy
listening to WLS to pass the time on a long midwestern drive won't have
the know-how or the equipment to null the incoming interference from
WCBS. The DXer trying to hear Algeria on 891 will have both, and
especially from coastal sites should have no real impediment at all.)
I would bet that the overall effect of IBOC on the clear channels will
be substantially LESS than the effect of the breakdown of those channels
that began in the forties and continued into the eighties. There was
lots of doom and gloom about THAT, too - and it ended up providing
opportunities for DXers, in the end. (How many of us have KXNT as our
sole NV log?)
On the regional channels, the effect will largely depend on which
stations take the plunge and which ones don't. On adjacents to channels
where few stations have gone IBOC, DX should still be fairly possible -
the few stations that go IBOC will essentially be single-source
generators that can be phased or nulled just as we now phase out
interfering analog signals.
It's on adjacents to channels where many stations adopt IBOC (at the low
end of the dial, for instance) - and, worse, on adjacents to the
graveyard channels *if* a fair number of graveyarders adopt IBOC - DXers
will probably feel the most pain. If even a third of the stations on
1230 and 1240 go IBOC, for instance (and that's no doubt a VERY high
estimate), the result on the adjacent channels will be similar to what
happened ON the graveyard channels as night powers were raised from 100
to 250 to 1000 watts - the noise floor will keep going up, and it'll be
a cloud of noise coming from many directions that's impossible to null.
There are excellent engineering arguments for barring night use of IBOC
by class IV stations completely, because of the effects it will have on
the adjacent channels (1220, 1250, 1330, 1350, 1390, 1410, 1440, 1460,
1480, 1500), but the FCC operates on politics and not engineering these
days, so that's irrelevant.
But I digress - while night IBOC will be a very real challenge to DXers,
and while it will certainly present huge obstacles to some forms of
DXing we now enjoy, it's not going to be the end of the world IF it's
approved (still far from a certainty). There are still too many stations
that won't adopt it, and too many channels where international treaties
will keep it a non-factor at night. (730 and 740, for instance, should
be very productive frequencies in most areas, since the only real
sources of night IBOC interference to them will come from single sources
on 720 and 750 that can be nulled easily.)
If we have any hope of hearing digital audio via skywave, it'll also
mean some changes in our antenna systems. Just as broadcasters are
learning that they need antenna systems that can tune up flat across 30
kHz of spectrum, I suspect we'll find that some of our antenna tuners no
longer do the job. Even on my semi-local WLGZ 990, the Recepter's much
happier with its own cheapo loop than with the peaky tuning on my McKay
Dymek DA5.
I'm not saying I *welcome* the challenge, or anything, but I'm curious
to see how it all works out, and since I can't really do anything to
stop it, I may as well see what the ride is like.
I'm already having fun seeing what I can do with the Recepter, which is
a truly lousy radio for DX purposes. I'm learning that the low-bitrate
data stream that rides ON the main channel, not in the sidebands, seems
to get out quite well. Down the road, if better radios arrive soon, that
could do for us on the AM side what RDS has done for FM DXers. Some of
those guys are now logging stations entirely on the basis of RDS hits.
No reason we can't do that, too, as the technology evolves.
If anything, I'd like a few MORE stations doing IBOC right now, just to
give me some targets to shoot for. So far, I've gotten the HD indicator
to light on WBZ, WCKY, WTWP and WGY, and have recovered callsign data
from WBZ, but no audio yet. What I really need is a good signal to my
west - a WJR, say - that will keep IBOC on just long enough after my
sunset to give me some idea of what might be possible where digital DX
is concerned. At 1746 EST, a few minutes before local sunset, WJR's
strong enough and stable enough here that I should be able to recover
IBOC audio, if it were running IBOC. Beats hiding my head in the sand
and hoping this will all go away, anyway...
s
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