Does a J-Pole Need a Balun?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N5XI, Jul 7, 2008.

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  1. N5XI

    N5XI Ham Member QRZ Page

    Hello, I just obtained an Arrow Antena OSJ 146/440 J-Pole, installed it, then later read that a Balun is needed for J-Poles. But is one needed for this J-Pole? http://www.arrowantennas.com/j-pole.html

    It appears some J-Poles say there should be, and some don't mention it.
    - ARRL Antenna Handbook (on 2m copper JPole), says 3 loops of coax 8" in diameter
    - http://www.n7qvc.com/amateur_radio/copper.html, no mention
    - http://www.alpharubicon.com/elect/jpolejaden.htm, no mention

    I didn’t leave enough coax to create a Balun from a few loops of coax. Does this specific Arrow J-Pole need a balun? I’m getting 1.4 SWR right now without one. What would be better with the coke balum? Would it improve SWR, reception (less noise), or anything else?

    If I do need a balun, is there one that’s just an inline PL-259 adapter I could screw between the feed and the antenna? Or should I cut some more coax to make the loops (I’d use PL-259 on each side with a gender changer to connect the two cables, there’d be loss, but if it’s needed, then so be it). If loops are used, what would you recommend? I’ve heard three loops 8” in diameter, is that right?

    Thanks!
     
  2. W6GQ

    W6GQ Swap Meet Moderator Volunteer Moderator QRZ Page

    Nope!

    No balum needed.
     
  3. W0EA

    W0EA Ham Member QRZ Page

    A choke balun wont change the SWR, but it will keep RF from flowing back on the braid (and causing "rf in the shack"). If you aren't having problems with rf burns or anything you're probably OK. If you ARE having problems, then get them fixed, it doesnt take much at 144 MHz to be over the FCC limits for exposure.
     
  4. W8GTF

    W8GTF Ham Member QRZ Page

    I own the same antenna and used it for several months (I'm even considering going back to it).

    I never used a balun, and it worked flawlessly. This was with the antenna mounted about 9 feet off the ground, and basically in an alley way (roughly equal distances from both ends) between two 2 story brick apartment structures that were atleast 200 yards long.
     
  5. W6GQ

    W6GQ Swap Meet Moderator Volunteer Moderator QRZ Page

  6. AC0FP

    AC0FP Ham Member QRZ Page

    KC5VXG,

    I have no experience with J-poles other than theory. If the manufacture didn't include a balun, one could assume its not required. In regards to the ARRL 2 meter J-Pole the fact that they tell you to put some loops in your coax indicates there is RF riding on the coax.

    What I would do is get a clip-on ferrite choke balun thats big enough to fit over your coax and install it at about 18 inches down the coax from the antenna. It may not make any difference in how the antenna works, but it should keep RF out of the shack.;)

    73,

    Frank:)
     
    Last edited: Jul 7, 2008
  7. N5XI

    N5XI Ham Member QRZ Page

    Official Response from Manufacturer

    I recieved an e-mail from Arrow Antennas (Allen Lowe, NØIMW):

    "A balun or choke is NOT needed for the OSJ. Only needed for J-Poles made of copper pipe."

    Thanks to everyone else for the quick reply! :)
     
  8. K6BTM

    K6BTM Ham Member QRZ Page


    NOT True ! I have fabricated both. With or without Baluns. J-Poles made of copper pipe work just fine with or without Baluns. Being a Purist, I put 1:1 Coax Baluns on them. Let it go and just use it. ;)
     
  9. G0GQK

    G0GQK Ham Member QRZ Page

    Its balum and diapole time again.

    GoGQK
     
  10. K0CMH

    K0CMH Ham Member QRZ Page

    Ih ave made and used any number of copper pipe j-poles, and made exact copies of the Arrow j-poles. In all my applications I have yet to have RF on the coax braid.

    Also, I personally know many persons using both j-poles and have no reports of RF on the coax braid. Also, from personal experience of operating many of these friends' j-poles, I have not experienced RF on the coax braid.

    I believe there is a remote possibility of the 2 meter and dual band j-pole antennas generating RF on the coax braid, but it appears to be very rare to me.

    About half the people I know do not use a balun on their j-poles, and the other half do make a coax balun (which I prefer to call an "RF Choke"). Every one that does add a choke does it "just in case".

    Bottom line, my experience says it is not needed unless you are having RF problems.
     
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