With all the antennas we're doing lately, a few guys have tried and it causes signal loss on the Hopper system, but I think a few have successfully diplexed Wallys. And I believe if you're using a power inserter for the OTA, you want it inline after the Diplexor
Ah, that's what I was thinking, too: Signal Loss! AFAIK, Dish MoCA 1.1 and 2.0 do NOT operate in the same band as OTA, and all OTA broadcast channels over 39 will soon be taken away from broadcasters, anyway. Now, the DirecTV DECA
does, indeed, operate within the OTA band, and it is pointless to combine OTA and DECA because it won't work due to interference.
I believe that ANY implementation of "MoCA" that operates in the OTA band can
NOT legally use the MoCA name or trademark (even on menu screens or diagnostic screens) because operating in the OTA band is NOT spec for MoCA. That is why DirecTV's out of spec "MoCA" MUST not carry the MoCA name or trademark--even though DirecTV is part of the Alliance and has rights to implement MoCA, but no right to do so in the OTA band under the name MoCA--so, DirecTV has to call their hardware that operates in the OTA band
DECA to avoid licensing dispute. I think there is a sanctioned/official MoCA band that operates in the Satellite IF (MoCA band E or F or something; I don't remember), but that--and hardware--
can be legally called MoCA and use the trademark is allowed because it meets MoCA spec, IIRC.
Please feel free to correct me on any of this. I take your word to the bank!

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