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I want to buy a radio antenna for my stereo in order to pick up a few farther-away stations clearly. The outputs from the antennae that I'm seeing are to coax cables, and the input to my stereo has 75 ohm and 300 ohm connectors. What sort of adapter do I need to get in order to connect the antenna to my stereo?

Here is a picture of the back of my stereo. I believe the connection to the antenna is a coax cable with F-male connectors.

enter image description here

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  • $\begingroup$ Pictures please. $\endgroup$ – Phil Frost - W8II Aug 8 '17 at 13:19
  • $\begingroup$ Most 75-ohm connectors are the female F connectors that coaxial cable for cable television and television and radio antennas usually use. It should screw right in. I do have an older Yamaha receiver from the 1990s that came with an adapter cable that adapted the jack on the receiver to the F connector. (My more modern receivers both have the F connector.) $\endgroup$ – Jim MacKenzie VE5EV Aug 8 '17 at 17:28
  • $\begingroup$ @PhilFrost-W8II added pics $\endgroup$ – flippz Aug 8 '17 at 18:16
  • $\begingroup$ Here is a photo of the unit you need: google.com/…: $\endgroup$ – SDsolar Aug 9 '17 at 1:07
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So what you have is binding posts (I assume) with a specified 75 Ω input. That's unusual, but let's run with it.

First of all, you can use a 75-300 Ω “matching transformer” that has the right ends, and it will probably work just fine (reception does not care very much about impedance mismatches), but it's not the way to get the absolute best performance.

Instead, what you want to do is to connect the 75 Ω cable directly with no transformer. You can make an adapter without needing to buy any specialized parts or solder anything:

  1. Find a friend who's throwing out some coax, or ask a cable TV installer for scraps, or worst case go buy from the hardware store:

    • a standard 75 Ω "F" connector coaxial cable, as short as you can find.
    • a "F" coupler (as you would use to connect two cables).
  2. Cut the cable, so you have a short piece with a connector on one end.

  3. Using a knife, wire stripper, or a coax stripping tool if you have one, carefully strip off the outermost insulation for an inch or so, revealing the braid (outer conductor).
  4. Unbraid the braid, then bundle the fine wires off to one side (so that they are not surrounding the center conductor any more) and lightly twist them together like they were a piece of stranded wire, for later convenience.

  5. Strip off the dielectric (insulation) around the center conductor, but not so far back it'll short against the shield.

  6. Use the coupler to attach this to the end of your antenna cable.
  7. Connect the shield wire to the "GND" binding post and the center wire to the "FM ANT" binding post. Make sure no stray wires from the shield are shorting.

    (Make sure they're not pulled down to short against each other by the weight of the coax — perhaps an adhesive cable clamp stuck onto the case over in the free space to the right would help as strain relief.)

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The 75 ohm connector on your receiver is designed for coaxial connections. The 300 ohm connector is for an antenna that uses a flat, two wire cable called twin lead.

You may need an adapter of some type to convert the connector that is on the end of the coaxial cable coming from the antenna to the type of connector on the back of your receiver if the two are not a match. These are commonly available. Post pictures of the two ends of the connection if you need assistance with the terminology to find an appropriate adapter.

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  • $\begingroup$ Yeah, that sounds right. I guess I need an adapter from the coaxial cable to twin lead? Something like this? $\endgroup$ – flippz Aug 8 '17 at 18:17
  • $\begingroup$ @flippz If you coax doesn't have a connector on it, I recommend just stripping back the coax and connecting the braid to the post labeled ground and the center conductor to the post labeled 75 ohms. If it has a connector, you might find it easier and more reliable to use a 75 ohm to 300 ohm balun. It converts the 75 ohm coax to a 300 connection. Screw one end on the coax connector and the other end goes to your 300 ohm posts. $\endgroup$ – Glenn W9IQ Aug 8 '17 at 20:11
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Just make sure if you use a 300 ohm adapter you strap it across the correct terminals.

if your not worried about poking your finger save your $5 and strip the coax, twist up the shield and lace it under the ground post then bend the center conductor like a J and hook it under the post directly to the right of "FM ANT."

I used to have a similar receiver many years ago where they were too cheap to put an F jack on but they did have a small little piece of metal to hold the coax down. Yours probably fell off...

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