NSA can legally acquire any signal at any time without restriction. It is limited in what it can do with communications of "US persons" that are acquired as part of the overall intake. USSID 18, NSA's manual for electronic interception, describes in great detail these procedures with particular emphasis on how to handle intercepts of US persons to comply with legal restrictions. So the agency can intercept everything in the electromagnetic spectrum, and apparently does so. And, if given a special order to do so, it can subject communications of US persons for analysis and reporting outside the agency. It does take a special procedure to do this which is described in the manual. One type of intercept that is unique, and that is data concerning crypto which may be acquired and stored in perpetuity for later analysis no matter from whom it is acquired, including US persons.