This picture shows where you connect a auxilary antenna on a Chamberlain MJ55 commercial door opener. I adapted a RCA plug, but I’m wanting to find the right one. I need whatever plugs into this to adapt to a standard coax screw on connector. The outer part measures 1/2 od 3/8 ID and the hole in the center prong is about 3/32.
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That looks a little like an MMCX, but there are hundreds of RF connectors out there, so it's hard to be sure without actually trying the mating piece.
You were right there's hundreds of these. My wife searched a long time. It appears that it's a favorite trick for companies to use an odd fitting for the antenna connection - to make you buy the 15$ coax + coathanger from them? Here's the site that says that:
http://wireless.gumph.org/content/3/7/011-cable-connectors.html
She took the pictures out to Radio Shack and there was a savvy guy that recognized it as a female PAL connector. They had a "male PAL" to type "F female" adaptor. It's a European connector.
Anybody that needs an auxilary antenna for one of these Liftmasters could just use a 15 ft length of TV cable coax and half a coat hanger for the antenna (some adaptation required to hook it on) and it should work fine (and save 52$).
You could always just solder a cable to the contacts on the back side of the PC board. Maybe even solder right to the connector. Terminate the cable any way you want.
Good luck.
Soldering that way likely wouldn't produce very good impedance matching.
I would expect the auxiliary antenna to provide the impedance match, the solder is just to make the connection. Given the nature of the signal, narrow band RF, I doubt impedance matching is a significant concern.
Given the nature of the signal I think impedance matching would be of considerable concern.