Hi Matthew,
I have 4 DTV receivers in use and through the registration process, I always thought that the way they init the cards marries the card to the receiver so that it cannot be swapped out or moved to another receiver.

So maybe in the case of the HD OTA reception, the card isn't accessed the same way as for DTV and it just needs something in the socket? Otherwise, if it does mimic DTV behavior, I don't think you can just plug in any old card....

Any thoughts? Thanks, Randy