The PHILCO Phorum

I have two philcos that I am working on a 50-925 and a 49-906. Both have a bakelite 4 prong plug for FM antenna. How many wires need to be used for a FM antenna andwhy did they do this?
thanks
Chris

In looking at the print for the radio it looks like pins 1 and 4 are the only ones used and also shows some sort of antenna that is possibly capacitively coupled to the line cord on pin 1. Perhaps Philco originally included this line antenna with the set but also allowed for a convenient connection to an external antenna? In any event, I believe most antennas that come with modern day receivers are usually center fed dipole type hence the two connections required. I'm guessing that you could take a modern day dipole type antenna and connect it to pins 1 and 4 on that plug.