Perhaps”unknown” was the wrong term. What I was meaning to ask is how do I find unoccupied frequencies so I can “listen” in peace. I’ve tried to find frequencies I assumed where “empty” if that’s the right word, but then I started receiving something, I couldn’t quite make it out.
Depends on the equipment you have. If you have a scanner, you can set it up to search between the band limits of the scanner. Back when I was young, and before the internet was something we all had access to, there were books of frequencies, or if you were lucky, you'd get a fuzzy copy of a list of local stuff. The rest of it was up to you to find. Using the 'search' function on the scanner was a favorite pass time.
Set the scanner up, let it run, see what you hear.
Or, get one of the cheap SDR radios that plug into your scanner and give you a nice spectrum display that will show you a wide slice of spectrum at once.
Yeah, most stuff —should— be licensed and show up on FCC searches, however, there's a lot of stuff that won't:
-Federal users don't fall under the FCC, they fall under the NTIA, and the NTIA doesn't have an easily searchable database like the FCC. Finding federal stuff can be a challenge.
-Unlicensed users. Yeah, there's a lot of users out there that assume the rules do not apply to them, or that "no one will know", or are not smart enough to understand. Pretty easy to find them.
-There's unlicensed or "license by rule" stuff that won't be well documented and those can be fun to search.
It's a good idea to know where to look, but that's kind of hard to do. A good place to start is to see where people should be, and compare that to what your scanner/receiver will cover.
Start here:
A good place to see assignable frequencies for public safety users is on the FCC Public Safety Pool page:
www.ecfr.gov
For business/industrial users, you can look here:
www.ecfr.gov
If you find something and want to figure out what it is, you can use the frequency search on this site, or you can use the FCC search page: