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jay_bob · #12 12-29-2013, 04:06 PM

That connector looks like a PL-259, which was used on American CB radios.

There was a predecessor to the cellular car phone, it was a shared spectrum radio telephone system. It went into service in the 1950s and was discontinued when cellular was introduced in 1983. That legacy system used shared frequencies so only one user in the whole city could be on that channel at any given time and there were only a few dozen available channels. The cost was dollars per minute to make or receive calls. Due to the limited capacity only the very wealthy or those who absolutely needed to be in touch 24/7 (like city leadership) had them.

trivia: I was living in Chicago when the cellular rollout occurred, and I met some of the engineers at Bell Labs that were working on it, since I lived in the western suburbs near the site of the Bell Labs facility that worked on the project.

The legacy mobile telephone worked on a lower frequency than modern cellular so the PL-259 would be an appropriate connector. IIRC it was in the 49 MHz band in the US - which got freed up after the 800 MHz cell phones came out in 1983, so the consumer cordless phones took over using the 49 MHz band.

American 800 MHz cellular system phones used the TNC connector. The prewire for cellular phone in my 98 E300D has the TNC connector in the trunk, which goes to the bumper mount antenna (they used the power mast antenna in the 96-97 210s and the 90s 124s). There is another piece of coax cable which ran from the trunk to the center console. This was meant for a docking cradle for a hand held phone - a major rarity in the mid 90s so it was just taped off in the harness on my car. The cellular phone system for the US models was made by Motorola with the M-B brand label. The electronics package in the trunk had a DB25 connector that carried all power and signal connections except the antenna. The handset connected via an 8P8C modular jack in the center console. There was also another 8P8C below the radio for the remote display head. This gave the ability to call up speed dial numbers and initiate or answer calls without having to take the phone handset out of the armrest.

I believe by the time they got to the second gen W210s that they were into the docking cradle system that accepted the Motorola StarTac phone. So those cars did away with the trunk mounted electronics. I believe you can get a Bluetooth adapter for that car and link your modern phone to it.

So if you have a 2nd gen 124 or 1st gen 210 and find a big DB25 connector in your trunk, or an 8P8C jack in your center console or behind the dash, that is for the Motorola analog cell phone system.