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Thread: Antenna connector help

  1. #1

    Default Antenna connector help

    Hi guys.

    I am in the process of making my first "homebrew" antenna, I have followed this video by K7AGE https://www.youtube.com/watch?v=HkmD3Sgz7Q0
    I have attched the copper wires to the so239 chassis mount. But I do not knwo what connector I need.

    I have RG58 coax which will connect to the so239 chassis mount, but the video doesnt show this part and I beleive he is using a different type of coax.

    This will be connect to a little baofeng UV 5r.

    So I need help on the specific type of connector to connect the rg58 cable to the so239 chassis mount as in the video, and a connector from the rg58 into the baofeng uv 5r

    Many thanks

  2. #2
    Sudden's Avatar
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    You would need a PL259 connector for the antenna end of the coax and a SMA to coax adapter for the Baofeng end. Something like this Ebay description --1x PL259 SMA Female to UHF Male RF Straight Pigtail Jumper RG58 Coax Cable 50cm I suggest the cable adapter because it reduces the stress on the Baofeng antenna socket when moving the radio about.
    You can adapt this antenna to have the 70cm wires attached and give you a dual band antenna. I did this and it is very easy to make.
    I'm leaving now to go find myself....if I arrive before I get back, please ask me to wait!

  3. #3

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    Quote Originally Posted by Sudden View Post
    You would need a PL259 connector for the antenna end of the coax and a SMA to coax adapter for the Baofeng end. Something like this Ebay description --1x PL259 SMA Female to UHF Male RF Straight Pigtail Jumper RG58 Coax Cable 50cm I suggest the cable adapter because it reduces the stress on the Baofeng antenna socket when moving the radio about.
    You can adapt this antenna to have the 70cm wires attached and give you a dual band antenna. I did this and it is very easy to make.
    Thats great thank you for your help, I would be interested in instructions on how to adapt this to have 70cm as well if you have them.

    Many thanks.

  4. #4

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    The wave for 2m is a perfectly decent antenna on UHF because it's then a wave and matches nicely - so you can use the same antenna on both bands without replugging. The strange thing is that the PL259 connector is called a UHF connector - when it's actually pretty rubbish at UHF, but OK for VHF. It will work of course, but something like BNC connectors are more reliable, easier to use and perform notably better. Usually made worse by the habit 259s have to be quite nastily made, often melted when put on and tending to jam!

  5. #5
    Sudden's Avatar
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    This is picture of the 70cm addition to the antenna. The blue wires are the 70cm ones and they are 6 inches long. I used the calculation of 234 divided by 433 to get the length.(This is from the video by K7AGE). I cut them a bit longer than required and bent the ends back to get the best swr.PIC_1314.JPG
    I'm leaving now to go find myself....if I arrive before I get back, please ask me to wait!

  6. #6

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    Not quite sure what you've done here from the picture. You have two ground plane elements cut for a quarter wave at 70cm, how long is the vertical, I assume the same length? If you cut it for 70cm, then it won't be much use at 2m, but as I mentioned above, if you cut it for 2m, it works pretty nicely at 70 - so you can use both bands!

  7. #7
    Sudden's Avatar
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    There are two vertical and two sets of ground plane elements. The blue is for 70cm and the other is for 2m the picture is focused on the 70cm part of the antenna and the 2m vertical is missing the top part in the picture but it is there.
    I'm leaving now to go find myself....if I arrive before I get back, please ask me to wait!

  8. #8

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    Ah - I see now. This really doesn't work that well. It's actually what is inside some of the white stick type scanner antennas. The problems are to do with parallel antenna elements - the ground plane is fine. Like I said, a wave 145MHz whip is also resonant as wave on UHF - both frequencies being close to 50 Ohm impedance - so two together create two good matches, in parallel, lowering the effective impedance, and effectively de-tuning the aerial.

    All you need to do are a few simple tests. Find a distant ham repeater and see how string it is - ideally a weakish one. Try it with one vertical, then add the second and see if it is better or worse. Try the same thing at UHF and VHF. The strongest performer for what you want it to do will be the ideal. The white stick scanner versions mainly get away with it because each wave inside is cut for a harmonically unrelated band - so while one vertical is near 50 Ohms, the others are much higher, and paralleling them has less impact.

    Playing with antennas is a kind of torture/fun thing to do. All to do with success v failure, but also with how much failure, as in if you want to receive multiple frequencies, you might have to live with slightly worse performance on some frequencies to get anything on others.

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