Mine was a TRS-80 CoCo:
It had a “game cartridge” port…which is also where the modem got plugged in. The port is on the right side of the machine.
This bad boy plugged right into a TV, like the Commodores and Amigas. Channel 3 or Channel 4? Your choice lol.
le modem:
tagging @Malkuth and @FireDragon