[Wswss] Re: [PNWVHFS] j-pole antennas---feed point question

[Bob Swift]

Hi Len & the group,

I feed mine a little different them most. I attach a SO 239 to the shorting bar by drilling a hole large enough for the lug to fit through about 1/4", then I take a 5/8" bit and hollow the bottom of the bar so the SO 239 will fit flush then you solder a piece of 12 or 14 ga. house wire to the lug and go up 4" to 6" bend a L in the wire to go over to the long side and wind about 9 turns going up as close together as you can ( the windings should stay tight on the rod ) then you attach your coax and a good analyzer and gently move the coil up or down just a little and when the SWR starts to drop you can trim about 1/8" off of the coil and watch the SWR, it should wind up being flat by small adjustments up or down and trimming. It looks and sounds crazy but it works great for me. I use a SS 102" CB whip on mine with a 1"x1/2"x3" flat allum. stock drilled and taped to except set screws to keep the antenna in ajustment. The 102" whip I cut up about 72" from the threaded end and leave the threaded end on to aid in mounting, this is the 59" side, then the piece that is left over is used for the short side @ 19". I do find that the J-pole does have a null off of one side but I don't remember which side it is on. You can put a carrier on it and walk around it with your FS meter and find it but it don't seem to affect it's operation, great little antenna and a fun project. You do need a piece of flat nonconductive stock to go between the top of the short rod over to the long one to keep them from moving around in the wind, mobile or base.

Good luck and Happy New Year to all.

73  Bob
W7ARR / CN92bc


  ----- Original Message ----- 
  From: Len Gwinn<mailto:compmtn at instawave.net> 
  To: PNWVHFS<mailto:pnwvhfs at googlegroups.com> ; wswss at mailman.qth.net<mailto:wswss at mailman.qth.net> 
  Sent: Friday, December 26, 2008 7:26 PM
  Subject: [PNWVHFS] j-pole antennas---feed point question


  QUESTION  from  WA6KLK

  In building a few copper j-poles for a few friends for the fm bands,  I have a VERY confusing point.

  Some of the schematics show the center conductor of the coax to the short leg of the j,  others show it to the long leg of the j.

  Why the difference ??    Does it make any difference  ??

  I can build them but now am  a bit confused for the feed due to the many many  designs of feed, ie, which conductor to which leg of the j.  I have done both and not really noted a difference but why ???  

  Common thinking by a couple of folks here is that the center connector should be to the short leg, ie, like the feed of a gamma match or shuch on a beam.    ----    Then again, a couple say feed the center conductor to the long leg as that is the "hot" leg and "more" metal in the air.

  Thanks and any other information as to why would be appreciated  !!

  Thanks !!!

  73  Len  WA6KLK


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