Helping out a friend with a picture or two of the Astec UM1233 RF Modulator’s inner workings. If you’re curious, it’s a device which was incredibly popular in the 80s and 90s in home computers, and takes video and audio as an input and turns them into either VHF or UHF (depending on country) radiofrequency signals – the same signals as analogue TV tuners expect to receive. If you crack open a ZX80, ZX81, Spectrum of almost any model, Commodore 64, ORIC, Newbrain, Dragon – almost any 80s microcomputer aimed at the home market – you’ll probably find one of these.

4 thoughts on “The Astec UM1233 RF Modulator

  1. Got my first one of these in the year 2007! Needed my PS2 to work on an old tv. It’s probably a little different internally to what you’ve got there, though.

  2. Pingback: The Mystery of the Missing Video Signal » Perception is Truth

  3. As fat as I can see these modulators do NOT have an integral sound channel. If you think about it there are only two input connections , vcc and video.

    However it is quite possible that the computer pcb adds an FM 6 mHz audio channel to the video signal.

  4. You’re right – this particular model doesn’t do audio, as it’s from a ZX81. There are others, used in things like the Commodore 64 and Sega Master System, which do.

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