Re: [IRCA] A Perfect Example

[Scott Fybush <scott@xxxxxxxxxx>]

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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