Some good questions, let me see if I can answer them in a way that makes sense. No guarantee, I'm not a lawyer....
Sorry, but I don’t see either of those as prohibiting ownership of a radio capable of operating on Part 90 frequencies if you do not have a valid Part 90 license.
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Nothing I see in (a) addresses the situation of an unlicensed person not associated with any licensee being in physical possession of equipment capable of operation on Part 90 frequencies. However, if that is true, then the passion of Part 90 capable equipment by a ham operator who has no Part 90 involvement would also be illegal.
Possession of a radio -capable- of transmitting on part 90 frequencies isn't an issue. What the quoted rule part say is that "no person shall program into a transmitter frequencies for which the licensee using the transmitter is not authorized."
Remember, this is Part 90 rules and those rules ONLY apply on Part 90 frequencies. You cannot take a Part 90 radio and PROGRAM in Part 90 frequencies (for transmitting) that you are not licensed for.
Lets break it down like this, and answer these questions. Either: (1) it is illegal for a ham with no Part 90 involvement to operate repurposed Part 90 equipment on the ham bands, as it still has the ability to transmit on Part 90 frequencies, or (2) it is not illegal for a ham to operate repurposed Part 90 equipment on the ham bands.
OK, again, good questions.
(1) It is NOT illegal for a ham with no Part 90 involvement to operate repurposed Part 90 equipment on the ham bands. It's a fairly common thing. In fact, many repeaters are repurposed Part 90 repeaters.
(2) It is not illegal for a ham to operate repurposed Part 90 equipment on the ham band. I do it with my Part 90 radios. It's done with repurposed commercial repeaters. "Back in the day" it was difficult to find "amateur" VHF and UHF FM mobile radios. Many hams used retuned commercial equipment.
I'll go a step further. I worked with a guy for many years that was running an old AM broadcast transmitter on the 160 meter amateur radio band.
In the event of (1) then yes, possession of modified radio gear, opened up, would be contrary to regulation. In the event of (2) simple possession of such gear would not be illegal, although for sure, and inarguably, operation of such gear would be illegal on Part 90 frequencies.
OK, I might be confused by what you are asking here. If the above didn't answer it, let me know. But here, let me see if I can answer it a bit better...
(1) Possession of "modified" radio gear, opened up is a complicated question depending on the radio (amateur or commercial) and where you are using it.
For a radio to be legal for use on a specific frequency, it must be type accepted by the FCC for the rule part(s) that applies to that frequency.
A modified amateur radio, which has NO type certification on the TRANSMITTER is legal for use on amateur radio bands. If it's been modified to operate outside the amateur radio bands, it's still legal. What's against the rules is to TRANSMIT with a modified amateur radio (with no type certification on the transmitter) on non-amateur radio frequencies. In other words, you cannot TRANSMIT an amateur radio that has no type certification on the transmitter on Part 90 frequencies. This would violate the Part 90 rule that requires transmitters used in Part 90 to be type certified for Part 90.
Since amateur radio transmitters do NOT require type certification, it's perfectly legal to use a transmitter that meets the requirements of amateur radio rules to transmit on the amateur radio frequencies. This includes Part 90 radios, old AM broadcast transmitters, etc.
Where things get confusing is when the Part 90 radio you want to use on amateur radio frequencies requires internal modifications to work properly on amateur frequencies. Once you modify the Part 90 radio to do what you want, it's Part 90 certification is now void. That's OK if all you do is use it on amateur radio frequencies. What you cannot do is use it on Part 90 frequencies since the type certification has been nullified by the modification.
So what is the answer? 1, hams cannot use Part 90 gear on Part 97 frequencies, or 2, hams can use Part 90 gear on Part 97 frequencies?
T!
Amateur radio licensees can use Part 90 radios on Part 97 frequencies.
Let me know if you need some clarification on this. I'm happy to oblige.