[BC] IBOC interference contours

[Chuck Hutton]

Blown way out of proportion? Let's look at the numbers..... The center of
Saline is 6 miles from the edge of Ann Arbor. The driving distance between
the center of Saline and the center of Ann Arbor is 9.7 driving miles. Let's
say 8 air miles. That hardly invalidates referring to WLBY as "Ann Arbor".

We all know Radio Locator is not exact, but look at the contours at
http://www.radio-locator.com/cgi-bin/pat?call=WLBY&service=AM&status=L&hours
=D and you'll see the 2.5 mV contour is way, way past AA. Make your own
guess for the 5 mV contour, but to me AA is surely in the contour. If your
conductivity comment is accurate, they still would seem to have a 5 mV/m
signal over much of AA.

But the proof is in the pudding. If people in AA were listening to WTBY and
they are now experiencing interference, we should at least investigate their
claims before saying they have blown the thing way out of proportion.

To pooh-pooh the interference claims on only this basis strikes me as poor
analysis.


Chuck


Date: Wed, 19 Jul 2006 22:19:04 EDT
From: RSTYPE at aol.com

It appears to me that both of these cases have been blown way out of
proportion (if something is repeated often enough it must be true).

WLBY (1290) is not licensed to Ann Arbor.  It is licensed to Saline, to the
southwest of Ann  Arbor and has the nulls of its directional pattern in the
direction of Ann Arbor.  Contrary to what some here have claimed, it does
not place its 5 mV/m contour over Ann Arbor, especially when one considers
that the actual soil conductivity in the Ann Arbor area is less than the 8
mS/m value specified on the M3 map, even in the winter.  In a past life, I
spent some time as a chief in Ann Arbor and distinctly recall that the
station had a marginal signal in most of Ann Arbor.

Findlay is not located within the 0.5 mV/m protected daytime contour for
WLJM
(940) and is predicted to receive daytime interference to its groundwave
service area in the Findlay area from the analog facilities of WWJ.  This
situation existed long before WWJ implemented IBOC operation (and long
before they improved their daytime operating facilities from 5 kilowatts
nondirectional to 50 kilowatts directional).  I also spent time in the
distant past working in the Lima market and actually designed and tuned the
presently licensed WLJM pattern.

One thing everyone needs to remember is that, even without IBOC, areas
outside a station's protected daytime contour where it may presently have a
"listenable" signal can, and always could, be lost to interference resulting
from modifications and improvements to other station's analog facilities.

Roy Stype
Carl E. Smith Consulting Engineers