[BC] Re:Real cases of IBOC interference wanted for research purposes

[Tom Taggart]

I can see another -and more ominous turn- in the IBOC debate. Looks like we have more consultants going over to the "dark side."

Yes, in many cases the interference protection betweent two adjacent AM stations is 1 to 1, that is, .5 to .5 . And for many stations, there is quite adequate reception at this contour daytime, with perhaps some minimal "monkey-chatter" from the other station.

Pre-IBOC

The example I site of WLJM Lima and WWJ Detroit we actually have WWJ's .25 just approaching WLJM's .5 in Hancock County, Ohio (Findlay). Hence this is a 2 to 1 signal for WLJM. Without IBOC this produces a listenable signal at the WLJM .5, for WWJ's 940 signal is barely noticable.

The WWJ IBOC signal places destructive interference on the adjacent channel.  It matters not whether this is "inside the mask" or not.
The operation of IBOC means that .5 is no longer a "protected contour," instead some higher value of signal is required before one can reach the same level of "interference free" signal one had with the .5 contour before IBOC.

This is a significant change in the protected coverage of an AM signal. It should not be done by the Commission by a blanket grant of approval for IBOC without case by case consideration of existing station's coverage.
--