The 40-Year-Old Cable Modem (part 1)
Channel: Jared Boone
Date: 17/04/2024

Technical deep-dive into one of the very first cable data modems -- from 1983!

The NABU PC and Network Adaptor were an amazing technical achievement that never caught on commercially, but pioneered high-speed cable network data software distribution. Follow along as I take apart one of these cable modems and try to get it to work again, nearly forty years after the original NABU Network service shut down.

We'll delve briefly into how cable TV tuners work, including frequency mixers, tunable oscillators and phase-locked loops (PLLs), automatic gain control, quadrature demodulators, and offset quadrature phase shift keyed (O-QPSK) demodulation using discrete logic chips.

Equipment used include an oscilloscope, RF signal generator, RF spectrum analyzer, digital logic analyzer, voltmeter, and continuity tester.

This work is open-source and documented on GitHub:
https://github.com/jboone/nabu-network-adapter

For more hardware projects and hacks involving retro-computers, music and audio, and amateur and software-defined radio, please subscribe!

Acoustic coupler modem video clip credit: TV Ontario's "Bits and Bytes" episode 5, "Communications Between Computers", 1983