Unlicensed Radio

In Europe there's not only power limitations but also duty cycle on some bands. Eg on 868Mhz you can only transmit 1% of the time.

I don't think the equivalent US band of 915Mhz has this, and it has a much higher maximum power which is really nice. Wish we had something like this here.

> all RF spectrum belongs to the public. The FCC does not own it,

I wish the FCC and more radio enthusiasts also understood that. Its amazing how many epochal inventions in radio have come to the public through getting around the FCC one way or another.

Yes, the limitations are due to device certification under part 15. However, this is in no way an implied license, as "license" has specific meaning within the context of various parts of the FCC regulations. Part 15 covers unlicensed radiators, so essentially "licensed" and "part 15" are antonyms. This is most significant in that licensing almost always implies some degree of protection from interference (although it may be rather limited), while part 15 devices receive no such protection... when someone interferes with your WiFi, you cannot complain to the FCC (there's some recourse related to the legality of devices, but you cannot for example seek a license modification to address the interference as licensed users generally can to some degree). The existence of "soft licensed" services such as the part 95 services somewhat complicates this as there are services like family radio service (part 95B) that are "licensed by rule," meaning that there is an implicit license, but that somewhat illustrates the point: part 95B radios like the common consumer Motorolas and Midlands are implicitly licensed, WiFi is not! FRS has (limited) regulatory protection from interference, WiFi does not. FRS has limitations on nature of usage, Part 15 has none, but the device must be certified to meet part 15 specs for emissions.

The whole "part 15" thing gets more into device certification, which I mentioned in the post I will discuss in the future as it's a topic all of its own. The history of part 15 device certification is closely related to the history of the ISM bands in some ways, but they are not 1:1, as part 15 covers both unintentional/incidental radiators (essentially all electronic devices) as well as intentional radiators which do not have a license... microwave ovens and WiFi are the quintessential examples of the latter.

It is of course obvious that RF spectrum belongs to the public, but in the US it is regulated by both the FCC and the NTIA depending on the user and the importance of the ITU cannot be understated as many of these services have at least partial international coordination. Certain radio licenses in the US will also require the approval of either Industry Canada or Mexico's IFT, although this is required under FCC regulations some of which implement treaty obligations. That said, I live in the US and am not a radio technician in the federal government (which is generally exempt from FCC regulations), so I tend to stick to what I know best: 47 CFR! It's also important to understand that in most cases the FCC does not coordinate spectrum usage on a level more granular than services and instead leaves it to other government agencies or private organizations, within the scope of each service. Part 90 is an interesting example, which is FCC licensed on a frequency level but coordinated by private companies for profit (the FCC just approves whatever frequency the private frequency coordinator recommends). I'll probably write on this in the future.

He's talking about these: [1]

They're cheap VHF FM analog handheld radios. Prices start around US$30. They can emit on the 462 MHz and 467 MHz Family Radio Service and General Mobile Radio Service bands, usable by anyone in the US and. That's fine. They can also emit in amateur radio bands, at higher power (8 watts claimed), which requires a ham license. The device controls do not make much of a distinction between the two modes. They're often used in the ham bands by non-hams, mostly preppers, hunters, militias, and people who own too much camo. This annoys radio hams.

[1] https://baofengradio.us/

In my experience it used to be common for rural PDs and FDs to just have every frequency someone could think of, within band, programmed into their radios regardless of authorization. I've even seen a rural PD distribute amateur radios to unlicensed officers as part of very half-thought-out emcomm plan.

This is getting less common these days as more and more rural public safety organizations transition to state-run trunking networks.

No; in the US, for example, Part 15 devices are, I think, limited to a maximum of 1W transmitted power at 2.4GHz, and 4W of EIRP (effective isotropic radiated power). i.e. maximum antenna gain of 6dBi at full power.

For fixed, point-to-point installations there is a special rule in effect: you can get more EIRP by having higher gain antennas as long as you back off the power; e.g. you can drop down to 22dBm (159mW) but have a 30dBi antenna and get 52dBm (159W) of EIRP.

A 30dBi antenna at 2.4GHz is, by the way, something like a 1.5 meter diameter parabolic grid.

2.4GHz is unlicensed, but through a few different routes FCC regulations prohibit operating, distributing, marketing, etc an intentional radiator (and many types of unintentional/incidental radiators) without an equipment authorization or device certification. So the pedantic answer is that you can do whatever you want in 2.4GHz but you can't do it using whatever device you want, which creates limitations of generally 1W as sort of the simplest answer.

> Could I emit 500W or more with whatever modulation or lack thereof and not be prosecuted

You could emit 500w in the 2.4GHz ISM band legally as a ham radio operator, as there is an overlapping ham allocation, so long as you complied with the ham requirements (which limits you somewhat on the 'whatever modulation' front).

But why would you? You're limited to line of sight communications -- far less than 500w will get you to the horizon. :P The only application I can think of for 500w at 2.4GHz would be moon-bounce. :)

Outside of the ham radio overlap, any intentional transmission in that band would have to be via a type-certified device. ... So it's more a question of what devices the fcc will certify than what you're able to do.

"Unlicensed" does not mean "Unregulated". There are still type-approval requirements for almost all transmitters (except Amateur radio where the responsibility falls on the licensed operator, rather than the actual equipment).

Much of 5ghz also requires DFS which can be a pain.