I'm guessing RF is going to be regionally different, if it's an NTSC toploader and you're trying to connect to a PAL television, you'll want to get a NTSC VCR or similar with its own demodulator, and get RCA composite video from that. Or you could try tuning into the RF signal on different channels on the television. Just a guess.
A more thorough solution would be to get the toploader modded for composite video, have a NESRGB board installed, or wait for the HDMI kit by Kevtris.