Well, I am rather a newbie on this forum, so if I have stirred any nests that shouldn't have been stirred, I apologize for that.
But, over the years, I have asked at least a dozen of these "Regulation Charlies" who believed that there were general modulation bandwidth limits in amateur radio to show me the rule -- but none of them could; not in 1983, not in 1993, not in 2003, and not now.
There is no such rule, and I think it's important for every amateur to know that. If a fellow ham starts up a 5-kHz-wide SSB QSO (or 10-kHz-wide AM QSO) on an empty swathe of spectrum in any band, he's doing nothing wrong, and people who arrive later are bound not to intentionally interfere with his QSO or fire up in his bandwidth until he's done.
Of course, the same is true in reverse: If there's no clear area of the band to fit such a signal, the fidelity enthusiast is bound to reduce his bandwidth or wait until there is, and not splash over on existing QSOs. The rule against intentional interference does indeed exist -- and, even if it didn't, I think the part of the amateur's code that states that "The amateur is considerate; never knowingly operating in such a way as to lessen the pleasure of others" should always apply.
