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I was recently given an older, but really nice broadcast FM receiver (88-108Mhz) by neighbor, but I am confused by the antenna connector and labeling. for the FM antenna connection, there are two spring lock jacks, and it is clearly labeled 75Ω, but every other reference I can find out on the interwebs refers to 75Ω being a coax antenna, and being sub-optimal for FM.

I can get a 300Ω dipole, and a 75Ω/300Ω balun adaptor, but all the adapters go to coax. Can I cut a chunk of Coax, plug one end into the balun, and on the other end stirp the insulation, plug the shield in one clip, and the conductor in the other on the receiver? Is there a better option (DIY or commercial)? Range is not a huge issue, I have plenty of FM options close to home.

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In general, impedance mismatches are not very important for receiving. Unlike a transmitter, you cannot damage a receiver with a mismatch. You miss some of the signal power that you could have gotten, but this is likely to be completely insignificant compared to e.g. the positioning and design of the antenna itself.

Get the 300 Ω specified antenna and just wire it in. It'll be fine. Or you can try using an impedance transformer as you proposed and see if it makes a difference, if you don't mind the price of the parts.

The best explanation I can think of for them specifying 75 Ω for a wire-terminal antenna input is that they used a receiver module designed for a 75 Ω input but didn't bother with the expense of a coaxial connector on the back. In which case, they're expecting you to just string a piece of wire from the antenna terminal, which will make a perfectly fine receiving antenna (just like one of those telescoping rod antennas) while having a fairly unpredictable impedance.

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  • $\begingroup$ Very good, thank you for the explanation. No risk of damaging the equipment then? $\endgroup$ – Butters Jul 4 '17 at 20:32
  • $\begingroup$ @Butters That's right. $\endgroup$ – Kevin Reid AG6YO Jul 4 '17 at 20:38

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