Early Model 1's had a serial port at the back, but I am fairly sure all NTSC-U versions had an RF jack.
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I don't have a pic, but I remember it was just a coaxial connection, similar to RCA, but a little bit smaller, and without the big protruding pin. I would describe it as almost like BNC, but without the locking mechanism. I'll try and get a look at it if I get a chance, but I rarely visit the old store and it may have been sold or put in storage.
So is the one without the license screen worth more? If so how much? Thanks.