I am not very experienced with signals, but something that has occurred to me while reading on various ways we are searching for ET signals, is that it seems most people rule out a signal unless it's in a narrow band. Is there any literature about treating signals that span a broad range of frequencies? This came from thinking that perhaps instead of utilizing a narrow band to send out a message, perhaps a theoretical ET might send their messages back and forth in a single burst, where the data, instead of "progressing" by time, progresses by frequency.
Possibility or gross concept error?
Who has attempted looking signals in this manner?