Add US433 regulatory domains

[MUSTARDTIGERFPV]

What this PR accomplishes

Adds 2 new regulatory domains, US433 and US433-Wide. US433 is 8 hops in the 4.75MHz between 433.25MHz and 438MHz, while US433-Wide is 20 hops in the 14.5MHz between 423.5MHz and 438MHz. Expanding these bands will reduce the chance of interference while running 433MHz ExpressLRS links, enable Gemini 433MHz to run without self-interference, and allows more 433MHz ExpressLRS users to run simultaneously without concern.

Rationale

The existing AU433/EU433 regulatory domains have quite restricted frequency space, 1MHz and 1.35MHz respectively, only permitting 3 hop channels for 433MHz users in those regulatory domains. In the US, licensed hams are permitted the use of 420-450MHz, a total of 30MHz wide, as the 70cm ham band. Two caveats exist for this band:

1. The ARRL band plan generally respected in the US only designates 433-435MHz as "auxiliary links" which is the closest thing we can map our use case to. However, the band plan is a "voluntary division of a band to avoid interference between incompatible modes" and isn't a requirement. So long as we're respectful in other ways, rigid adherence isn't required.
2. In the areas north of Line A and east of Line C emissions between 420MHz-430MHz are forbidden due to a treaty with Canada.

Prior Art

Analysis of other 433MHz control link systems shows us that in spite of the voluntary band plan, these wider frequencies are already in common use. I have taken SDR traces of my DragonLink V3 system operating in each of its 3 band modes, "Normal", "Wideband", and "Ultra Wideband", and recorded what appear to be the start/stop frequencies for each of these bands, which I reproduced at the bottom.

Discussion

Given the way the 70cm band is divided up in the ARRL band plan, it's difficult to find a contiguous chunk of spectrum that fits our use cases. I chatted with a few local hams that run significant 70cm repeater setups however, and all agreed that the numbers I chose here were reasonable, and believed this wouldn't pose any significant problems given our power output will max out at 1W in a regulatory sense, and 50mW in a practical sense for 99% of users.

Outcome

With all of this in mind, I mapped the frequency selections from DragonLink directly into the ExpressLRS FHSS tables. To date, I have heard no complaints from hams about DragonLink operations in the 70cm space, ergo I suspect we'll not hear any either (especially considering our 1-2 order of magnitude power reduction to achieve the same range). I have tested these on my equipment and it seems to perform quite well.

Feedback

1. Should we have 2 different US domains? I like the flexibility, but it's yet another variable. I suspect the very small number of users who use 433MHz makes this a non-issue, but it's worth discussion.
2. How many hops should we use? AU433/EU433 are definitely overprovisioned in hop count per MHz. FCC915 accounts for an almost exactly 100kHz guard band around the 500kHz emission we use, so I took that into consideration. Doing similar for US433 would arrive at 8/25 hops respectively for US433/US433-Wide, but setting 8/20 gives us a little more room to breathe in Wide mode (and is likely to cause a little less disruption to other users of the band).
3. Should we consider restricting power output to 100mW max when US433-Wide is used? This might be a way to run a little more respectfully, even if DragonLink doesn't make the same concession.

Data

Band	Frequency Start	Frequency Stop	Width	# of 500kHz channels available	# of 600kHz channels available	Hops allocated	Configured Hops/MHz
DragonLink Normal	433.25	438	4.75	9.5	7.916666667	?
DragonLink Wideband	428.5	438	9.5	19	15.83333333	?
DragonLink Ultra Wideband	423.5	438	14.5	29	24.16666667	?
ELRS FCC915	903.5	926.9	23.4	46.8	39	40	1.709401709
ELRS AU433	433.42	434.42	1	2	1.666666667	3	3
ELRS EU433	433.1	434.45	1.35	2.7	2.25	3	2.222222222
ELRS US433	433.25	438	4.75	9.5	7.916666667	8	1.684210526
ELRS US433-Wide	423.5	438	14.5	29	24.16666667	20	1.379310345

[MykhailoVyn]

Please tell me on what equipment have you tested these changes?
Is it possible to configure this equipment to use even wider frequency hopping range, provided that I have permission to use those frequencies?
And whether it is possible on regular hardware.
Thank you!

[mr-sour]

Just got my 433 gear in today! I will do a test, is there anything specific we would like verified by a second person? What kind of logs would the devs like to see?