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When is a new digital protocol considered "documented publicly" enough to be used for amateur radio transmissions?

Part 97 states the following about prohibited communications:

(a) No amateur station shall transmit: ... (4) Music using a phone emission except as specifically provided elsewhere in this section; communications intended to facilitate a criminal act; messages encoded for the purpose of obscuring their meaning, except as otherwise provided herein; obscene or indecent words or language; or false or deceptive messages, signals or identification.

This answer explains that it's OK to use "any technique whose technical characteristics have been documented publicly".1 But what counts as being documented publicly? An academic paper? Simply publishing the specification on a public website? Or is there some other standard?

Footnotes:

  1. Apparently as per 47 CFR 97.309(b) and 97.307(f) there are certain bands where it's allowed to use an "unspecified digital code", which appears to mean encodings that are not necessarily publicly documented.
James KE5JOO
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TL;DR - It comes down to the purpose of the encoding/encryption. If the purpose is to obscure the meaning of the communication, it's illegal. If the purpose of the encryption/encoding is anything else, it's fine.

There are several examples of digital communications protocols that are actively in use, and some of them quite popular, whose encoding or decoding algorithms are not publicly available. Probably the biggest of those is D-Star.

D-STAR uses a closed-source proprietary voice codec (AMBE) that's patented by Digital Voice Systems, Inc. (DVSI)[16] because it was the highest quality and only codec available in silicon when the system was released. Amateur radio operators do not have access to the specification of this codec or the rights to implement it on their own without buying a licensed product. (https://en.wikipedia.org/wiki/D-STAR#Criticisms)

According to 47 CFR § 97.113(a)(4):

No amateur station shall transmit ... messages encoded for the purpose of obscuring their meaning, except as otherwise provided herein...

In the example of D-Star, the explanation was best said by KD0LIX:

DSTAR is a digital protocol for data and voice over RF. While there are plenty of arguments against closed or patent-encumbered protocols on amateur bands, DSTAR isn't encryption, it's just encoding. Since all DSTAR receivers can decode a DSTAR transmission on the same band, the barrier to recovering the meaning of a DSTAR message is relatively low, about \$200 for a Dv Dongle or \$500 for a transceiver. To contrast this with an encrypted radio, if you don't have the key, you're not going to be listening. (https://rsaxvc.net/blog/2014/2/1/Encryption_and_Amateur_Radio.html)

Joshua
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    D-STAR while not open is still publicly available; as you say, you just have to pay for it. (Technically, it's not under patent anymore, so there are free versions that were reverse engineered I believe.) It's proprietary, not encrypted. There's a popular HF digital protocol as well that is somewhat popular. – user10489 Jun 12 '22 at 04:30
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    There are also digital encodings that are only documented in public source code, with no programming language independent interoperability specification. It's arguable whether that constitutes a legal form of documentation. My assumption is that it is not (but IANAL). – hotpaw2 Jun 12 '22 at 15:53
  • @hotpaw2, the 'well documented' "requirement" doesn't exist. It's logical that it would have been a requirement, which is why (IMO) so many people think that it is. It all comes down to the intent. Having said that, I don't know everything, so if you know of something else, please share. 73 – Joshua Jun 13 '22 at 18:06
  • Thanks for this information! Out of curiosity, have there been any cases where the FCC took action against an operator for using a protocol that wasn't documented to their liking? Looking at such precedents (if any exist) might help shed more light on this question. – James KE5JOO Jun 14 '22 at 04:13
  • @Joshua, I could be wrong but I think the "well documented" requirement comes from 47 CFR 97.309(a)(4). – James KE5JOO Jun 14 '22 at 04:17
  • @JamesKE5JOO, that's a good point. But check out the very next section at 47 CFR 97.309(b) which says it's ok to use an unspecified (undocumented) code as long as its use is not "for the purpose of obscuring the meaning of any communication". – Joshua Jun 15 '22 at 14:46