What RF modulator do you have? The other problem is; if it's a modern box like this:
https://www.newark.com/stellar-labs/...irect-product#
that converts it to an ATSC QAM signal AND you have the Seiki TVs that do not have a QAM tuner then it will not work just like you can't decode digital CableTV signals in the RV park with the Seikis with no QAM tuner.