ECPA's prohibition on cracking "essential modulation parameters" applies to proprietary formats like iDEN. It is unlawful to decode these specific kinds of transmission.
The section about "scrambled or encryption" covers a separate issue. Even if the modulation parameters and the type of encryption are known, ECPA still forbids the general public to decrypt any radio transmissions.
Common sense dictates that if you are originating an encrypted transmission or if such is directed to you as the intended recipient, then you are not "the general public" with respect to that communication.
Every word in a statute has a purpose, and the division of a statute into paragraphs and sections means something. You can't just jumble up the law any way you want to get it to say what you wish were true, or to read ridiculous interpretations into it. In fact, there are standardized rules for legal construction that guide lawmakers and judges and should guide anyone who wants to know what the law means. For federal laws, consult the 2nd edition of American Jurisprudence (Am. Jur. 2d).