Feature request: configurable frequency range limits for regulatory / amateur radio compliance

[bartoszp1992]

Would it be possible to add an option to limit the frequency range used by ExpressLRS FHSS?

This would be useful for licensed amateur radio operators who may legally use higher transmit power, provided that all transmissions stay within the frequencies allowed by their licence and local band plan.

For example, in IARU Region 1 an operator may want to restrict 2.4 GHz ExpressLRS operation to 2300–2450 MHz, so the entire hopping sequence remains inside that range.

For example, I live in Europe and, in theory, as a licensed amateur radio operator I can legally use higher transmit power. However, I am still effectively limited to the CE LBT domain because there is currently no way to control or restrict the frequency range used by ExpressLRS.

A simple min_frequency / max_frequency build option, or a predefined amateur-radio frequency domain, could solve this.

The firmware could also verify that enough hopping channels remain available for reliable operation.

The intention is not to bypass regional RF regulations, but to allow licensed operators to keep ExpressLRS operation within the band covered by their amateur radio licence while using permitted higher power.

[readymaderc]

This is more important now that new products cannot get FCC certification due to the current administration regulations preventing new foreign-produced UAS components from getting FCC certifications. Amateur radio devices do not require FCC certification as long as they stay within the proper bands, however the current ELRS 2.4GHz band goes slightly above the amateur band. Note that the amateur rules limit RF power for "remote control" to 1W max, but the FCC generally considers the AVERAGE power output and not the peak output, so frequency hopping devices can usually operate at much higher power outputs.

[readymaderc]

FCC Part 97 (Amateur Radio) allows 2300-2450MHz, but that means that the onus is on the user to have a Ham Radio License to legally operate the equipment. There are also a bunch of requirements for Part 97, that would make ELRS incompatible, e.g. the pseudo-random hopping sequence based on a private bind-phrase. Not emitting a publicly readable callsign every 10 minutes and at the end of every transmission. It's just not possible to operate under Part 97.

We dealt directly with the FCC a few years back, about the same time they fined some of the other FPV retailers for selling non-compliant items.
-They reaffirmed that we were correct in our interpretation of the rules at the time and they requested that we add some language to our website to items being sold under amateur radio rules (nearly all FPV video transmitters and special RC systems at the time). This is still true of pretty much all analog video systems and some digital video systems.
-They had no issues with the various RC systems that were operating under the amateur radio rules (at that time it would have been the Scherrer system. Dragonlink, EZUHF, Crossfire, maybe others). Those are all FHSS systems. Including the fact that they didn't have a mechanism for broadcasting the amateur radio callsign.

Under §97.311(a), using a spreading code to operate an FHSS system is perfectly legal as long as the intent is to mitigate interference and improve link reliability, not to hide the communication. Furthermore, §97.215(b) explicitly states that control signals sent to a model craft are not considered codes or ciphers intended to obscure meaning. While the FHSS protocol itself is fine, you cannot apply actual cryptographic encryption (like AES-256) to your control or telemetry data.

We've been dealing with the amateur radio aspect of FPV/RC systems since 2009. A lot of people coming into the hobby or even selling products seem to be totally unaware of the FCC rules, which is why some FPV vendors were fined a few years back.

[readymaderc]

This is the specific US code referenced:

97.215 Telecommand of model craft:
An amateur station transmitting signals to control a model craft may be operated as follows:
(a) The station identification procedure is not required for transmissions directed only to the model craft, provided that a label indicating the station call sign and the station licensee’s name and address is affixed to the station transmitter.
(b) The control signals are not considered codes or ciphers intended to obscure the meaning of the communication.
(c) The transmitter power must not exceed 1 W.

97.311(a) SS emission transmissions by an amateur station are authorized only for communications between points within areas where the amateur service is regulated by the FCC and between an area where the amateur service is regulated by the FCC and an amateur station in another country that permits such communications. SS emission transmissions must not be used for the purpose of obscuring the meaning of any communication.

[pkendall64]

This is very good information, thanks for this.
So my reading then is that we could add an FCC97 2.4 Band which covers say 2300-2450 or some subset in that range and they'd be happy with that.

[readymaderc]

That would be great. For US amateur band compliance, that would be perfect. The OP for this thread mentioned the same frequency range for EU amateur range requirements, so maybe instead of FCC97 it could be AMATEUR or something like that?

[pkendall64]

I'd be OK with that

[jcer93705]

That freaking suck because even people who doesn't even fly much farther just los is effected. That sucks.