If the RCA is an over the air converter box then you would have to connect it to the TV with HDMI to get an HD picture.
If the RCA doesn't have HDMI then it will not give you HD. It was meant to be used with an analog TV that didn't have a digital tuner built in.
If the Samsung has a tuner then connect you antenna to it directly and follow the instructions in the TV owners manual on how to scan for channels.
If the Samsung is a monitor and doesn't have a built in tuner you want an ATSC over the air tuner rather than a converter box. That will have HDMI.