Daytime interference from WTOP's digital signal was found to be
"significant" at WARK's protected 0.50 mV/M contour, and "noticeable"
at its 0.75 mV/M contour.

Yet today, with noise and all, anything beyond the 5 mv/m contour is
pretty useless.

But what if you're in Nowheresville, Wyoming, and a few 5 mV/m AM
signals are all you've got? Tough luck, I guess?

The AM IBOC scheme is chronically myopic. Each station using it shall
only be concerned with their own primary local coverage area. But
what about when the skywaves kick in, and somebody else's "useless"
secondary coverage area suddenly lands smack-dab in the middle of your
primary coverage area? The middle of the band is a prime example.
Here in NJ at night, there's 1000 from Chicago, 1010 from NYC, 1020
from Pittsburgh, 1030 from Boston, 1040 from Des Moines, 1050 from
NYC, 1060 from Philly, 1080 from Hartford, 1090 from Baltimore, 1100
from Cleveland, 1110 from Charlotte, 1130 from NYC, 1140 from
Richmond, 1170 from Wheeling, 1180 from Rochester, 1190 from NYC
and/or Ft. Wayne, 1210 from Philly, and 1220 from Cleveland. Put IBOC
on all of these stations at night, and the mutual destruction would be
horrendous!

Some have suggested that allowance of nighttime IBOC, if any, should
be considered on the basis of whether two new AM broadcast signals, on
either side of the IBOC station's carrier and with the same power
level and signal pattern as the IBOC sidebands would have, would be
allowed according to the current FCC allocation scheme. In other
words, if WXYZ at 1000 kHz wanted to broadcast IBOC at night, it would
be judged on the basis of whether it would be legal to create two new
stations, 990 WXYZ-Lower and 1010 WXYZ-Upper, with the same power
level and signal pattern as the IBOC sidebands of WXYZ would have. In
most cases, the answer would be an emphatic NO.

For a 50,000 watt station, the total power used by the IBOC sidebands
is about 1500 watts. Split that in half, and that's about 750 watts
on each sideband. So, could 710 WOR fire up a new 750-watt station on
700 kHz and another new 750-watt station on 720 kHz at night?
Obviously, no -- the new 700 kHz "station" would violate the
protection that is afforded to 700 WLW, and likewise the new 720 kHz
"station" would walk all over 720 WGN. So, given the same parameters
of operation, how could WOR's IBOC sidebands (which can hardly be
called "In-Band, On-Channel") ever be allowed at night? iBiquity and
the NRSC think they should be... but what's going to happen in the
real world?

Mark my words -- if there's one thing that's going to finally kill off
AM radio entirely in North America, it's definitely going to be IBOC.