antenna choice

Discussion in 'Tuners' started by loudnoises, Mar 2, 2017.

  1. loudnoises

    loudnoises Escalates Quickly Subscriber

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    Pondside, NH
    So I'm having fun with different antennas, bumped it up another 6 feet and can now grab WERS 50 miles south in clear stereo, which was my last challenge.

    But of course I want more. I'm maxed out at about 18' currently.

    Towers aren't an option, but I've got this tree that's tempting me. I figure I can hoist something up to about 60', but obviously it's got to be suitable for hanging, and omnidirectional as there's no rotating.

    Can anyone relate experience using a j antenna? 1/2" copper seems choice, and the wind is pretty harsh up there, so the slim design is tempting. Any thoughts?
     
  2. I LIKE MUSIC

    I LIKE MUSIC Well-Known Member

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    You can't get there from here!
    A j-pole antenna is an end fed half wave antenna and works like one would expect for such an antenna. In the real world it might have a little gain over a dipole antenna.

    Properly built they are rugged and can be DC grounded which is not a bad thing, although in the real world the so called ground connection of the antenna is not at RF ground and grounding it may impact the performance of the antenna a little.

    They should be used with a good common mode RF choke at the antenna to help decouple the feed line.

    In your situation it may be a good choice. Like all outside antennas it should be in the least installed to the NEC and you might want to take lighting surge suppression up a little with the use of a surge discharge unit. PolyPhaser is one brand.

    There are several online design calculators for j-pole antennas and while the results of them do not always agree, the difference in the performance of the antennas is usually rather small.

    You will want to use the best quality, lowest loss feed line that you can if you are going for maximum performance and weather proof all of the outside connections.

    BTW, the j-pole antenna has a couple of very high impedance points and will be sensitive to objects, such as tree branches in its RF field and this may have an impact on the performance of the antenna. Try to keep it in the clear as much as possible.
     
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  3. Hobie1dog

    Hobie1dog Super Member

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    J pole calculator
    http://hamuniverse.com/jpole.html

    I use one for ham radio, 144mhz band with good success. I used solid aluminum rod instead of copper, so no soldering.
     
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  4. Hobie1dog

    Hobie1dog Super Member

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  5. loudnoises

    loudnoises Escalates Quickly Subscriber

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    Location:
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    Good food for thought, thanks gentlemen.

    I think i could hang it about 5-6' off the trunk, hopefully that'll be far enough. Even if it's no better than a dipole, the height should bring some improvement.

    Now the feed line... I've a giant spool of some dual 75ohm coax with ground wire the sat guy left here (score!). It's reputedly not the best quality. but has served me just fine.
    My reading claims that the 50ohm vs 75ohm works out to only about 1db of loss, and that's acceptable. I'm not going to pretend i fully understand half of this yet tho. At my level of fooling around, is there a real tangible benefit to sourcing higher quality coax, something 50ohm? this run will top out at under 100' from tip to tuner.

    Is there any reason i can't/shouldn't use this 75ohm? still just comparing antenna type performances, nothing being permanently installed, and sticking within FM range. And should i use the built in ground wire?

    likely rig something up this weekend. Or is there a more appropriate antenna design i should look at for this situation?
     

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