Here's the starkly simple reason why the "IBOC adjacent channel interference is okay, since the Commission allowed all those 'interference-generator' later-licensed stations" argument is completely specious.
If all of the "interference-generating" secondary stations contributing to the much-derided "degradation" of the AM band lined up in the FCC lobby tomorrow to surrender their licenses, and the current pop-count of AMs dropped from about 4700 to, say 2000 operating stations - the net effect on the success or failure of HD-AM would be...ZERO.
Martin Stabbert would still have turned off IBOC at night to keep WABC, WJR and WSB from killing each other. WBZ would still be clobbering its sister KDKA. The high-powered 1130s in the midwest would still be obliterated by KMOX. And it would still be WBAL vs. WTAM, WFAN vs. WSM, and on and on.
Don't take my word for it. Check this week's Radio World. Clear Channel and CBS are making selective decisions about which AMs they're leaving on with HD-AM at night because of mutual interference issues.
Blaming the IBOC nighttime mess on the presence of "secondary stations" is unsupportable.
Let's deal with some of the other assertions you guys advance. "Stations operating IBOC at night are in accordance with the rules?" There's a dirty little secret about that, whether or not you choose to believe it. Two prominent consulting engineers have informed me, off the record, that most of their client stations using IBOC-AM routinely fail to comply with the NRSC mask. If/when they do, the digital coverage is unsatisfactory. Look at Cris Alexander's screen shot in a recent RW and check the sidebands relative to the carrier. The only way that could have been accomplished would have been to reduce analog modulation to about 5%-10% long enough to take the picture. It's just another way IBOC stacks the deck. Cook the books, take the screen-scan, declare victory and go home. The FCC is clueless, of course.
Read Barry McLarnon's piece in the 12-5 RW. You can't reference noise levels below carrier level by selecting ONE digital carrier out of 25 in the passband of the affected station. There are 25 OFDM carriers there, and EACH one makes noise! The current -28 dBc suppression standard is like looking at traffic on the New York Thruway zooming at average speeds of 80 mph, aiming your radar gun at the geezer driving his 1958 Rambler American at 52 mph, and declaring: there's complete compliance with speed limits!
As far as WYSL's causing any harmful skywave to WHO, or compromising some DXer's ability to hear it in Batavia, I would say that's highly unlikely. Our nighttime limit towards WHO is 1.56 mv/m, and that monitor point (thanks, Kintronic!) typically runs about 0.40 mv/m. Compare that with the deafening skywave IBOC arriving from WBZ, and WYSL's contribution is nonexistent. C'mon, Radioman - you're "sure WYSL was interfering" with WHO?? Really? Got an aircheck of that? (I'm just kidding here, my friend, but maybe "you're spending too much time listening to Art Bell!")
BTW: WYSL carries Jim Bohannon overnight. So feel free to enjoy your favorite show on WYSL's egregiously interfering signal.
As far as Rochester listeners who have been deprived of nighttime service from Des Moines, WYSL moved from daytime-only on 1030 to unlimited hours on 1040 back in December 1997. We have never received a single communication in ten years from anyone upset about losing reception from WHO locally. Not one.
And finally, Radioman: "did we have a right to do that?" Do what? This is a "have you stopped beating your wife question." We have a right to be on at night. We comply with the rules, and our directional operation is absolutely within parameters. Unlike IBOC stations, we observe the NRSC mask. And if your premise is that WYSL is creating any measurable skywave interference to WHO (or CHUM, or WCHR) that's just wrong.