Re: [IRCA] [NRC-AM] WOR and IBOC

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Tuesday 18 September 2007 11:39, Marc DeLorenzo wrote:
> Bill has raised some excellent questions.  Unfortunately, I don't have
> answers but rather more questions.  According to Barry's list,
> http://topazdesigns.com/iboc/station-list.html, WLW IS running at IBOC at
> night.  Is this not true?   If WLW is running IBOC at night, I believe they
> will cause more interference to WOR than WGN will because they are closer
> to NYC.    Anyway, as Bill mentioned, the real issue is will WOR receive
> IBOC interference within it's NIF.  I'm sure Tom Ray is taking
> measurements.

You're right about WLW, they do have it on... more about that below, but let's 
take a step back first.

I have to ask: why all the focus on WOR?  Yes, Tom Ray has made himself the 
poster child for AM IBOC, but the question of whether or not they suffer from 
IBOC interference is not the crucial issue here.  An interesting issue to be 
sure, but not the crucial one.  The folks at WOR obviously had a good idea of 
what to expect from nighttime IBOC, and they decided they could live with it.
But WOR's situation is atypical for several reasons, and the fact that they've 
decided to tolerate some additional interference is, to me, not really 
relevant to the situations of all the other affected stations out there.  For 
one thing, WOR gets creamed fairly badly by a high power Cuban station, and 
they can't do anything about it.  So, they likely already have a relatively 
high NIF contour value... certainly worse than the average Class A, anyway.
The higher the current NIF, the less impact that IBOC interference will have.
The saving grace for WOR is the huge population base within a short distance 
of their transmitter.  The bottom line is that they've made a business 
decision that any loss in coverage is more than offset by being able to offer 
a digital service (of course, they severely miscalculated the potential 
popularity of HD radio, but that's another story).

Anyway, back to the WOR numbers... I calculate the field strength (10% 
skywave, for you technorati) of WGN at WOR to be 1.33 mV/m.  However, WLW is 
even stronger, at 1.91 mV/m.  Between the two of them, I arrive at an 
effective NIF value of 14.8 mV/m.  In other words, the hiss should start to 
be noticeable around WOR's 15 mV/m contour.  I would further speculate that 
it would become very annoying at around the 5 mV/m contour.  I don't know how 
this would compare with the current co-channel interference from Cuba, 
though.  I would think that it has to have some impact on their useful 
coverage, but I doubt if we'll get the straight goods on that from the WOR 
folks!

In any case, there are many other stations out there that have more to lose 
from IBOC interference than WOR, methinks.

Barry

-- 
Barry McLarnon  VE3JF  Ottawa, ON

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