There is a compartment located behind a small black cover on the back of the SLO-1800 for inserting an optional RF modulator. Once installed this little tool will send a broadcast signal from a screw-on coaxial terminal located nearby. TV channels 3 or 4 (switchable) are available. It just slides inside and mates up with a tongue-in-groove connector inside. The cover should be put back after installation. The location is identified in page three of these SLO-1800 pages. This modulator offers a way to see the picture. The outgoing signal could go to an antenna, television or VCR. It is analog NTSC 3.58 on 3 or 4 and it is independent of the A/V OUT connectors. To go to the product page featuring the RFU-634 modulator click here. To see the location for the coaxial screw-on connector click here. ©Misterßetamax go to homepage