I too, have seen 3.1 appear mysteriously in the last several weeks, the same channel as 28.3. I did see a promo on 3.1 about it, that they are broadcasting in hi-def. on 3.1 (720P).
Is 28.3 in 480i?
I have 2 devices for tuning OTA. One is a TVIX 6620 which has an ATSC tuner and a hard drive. It shows on screen brief audio/video specs of the signal (i.e 720p, DD 2.0). Strangely, when scanning it will pick up 28.1 but not the sub channels on 28. Therefore I don't know if 28.3 is broadcasting in 480i, but I assume it has in the past. (28.1 is useless to me since it is a shopping channel.)
My other OTA device is a Zenith DTT-901 converter box. It gets 28.1 and all the sub channels but has no readout wether the signal is SD or HD.
Channels 16, 26 and 28 are all related, owned by Courier Broadcasting. What a mess! For example, 26.4 runs the same episode of the same program repeatedly everyday for several weeks. They are showing all public domain stuff mostly from the 1950's (My Little Margie, I Married Joan, Racket Squad, One Step Beyond, Burns and Allen, 1950's Dragnet, etc). Also broadcast are some better known series that had some episodes or partial seasons slip into the public domain. For example there are handfuls of episodes from The Andy Griffith Show, The Beverly Hillbillies, Petticoat Junction, The Lucy Show and Mannix that have fallen into PD.
You'll only see the eps that went into PD, never the eps that the rights are still owned.
Perhaps if you have ever bought one of those bargain DVD sets that have 50 or 100 episodes of "classic comedy", you will find many of he same episodes broadcast. (Sorry to get a bit off track).
Channel 26.4 even shows some of those mental hygiene/social engineering films shown in classrooms from the 1950's and some mind numbing 'pubic information films' from the 60's. They call it "AV Club".
It is a painfully bad channel, yet still compelling and interesting, almost fascinating in its "badness". Their website is completely inaccurate (over a year out of date) and I have seen them broadcast on 26.4 brief screens showing the weather forecast that were over a month old! they send no PSIP information so no titles of current/upcoming programs are shown.
I love the 1950's stuff, the more obscure the better. Too bad they don't have their act together, I'd watch them often.