Another Jpole Question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KJ4QCV, Dec 22, 2009.

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  1. KJ4QCV

    KJ4QCV Ham Member QRZ Page

    I was noticing that the driven element on a 2 meter Jpole at 147mhz is 57.55" and on a 441 is 19.18.

    Now 19.18 x 3 = 57.55 Since it is an exact mutiple shouldn't a 2 meter tuned for 147mhz also resonate at 441. Therefore allowing to be used as a dual band antenna???

    Or am I way off the mark?:confused:
     
  2. W5DXP

    W5DXP Ham Member QRZ Page

    Nope, you are right about the resonance. Unfortunately, the 2m J-Pole is physically too long on 441 so most of the radiation is lost into space at a high radiation angle. However, some hams can hit some of the 441 repeaters with that antenna and that is all that matters to them. But don't expect any DX except maybe to the moon. :)

    This is the same problem as trying to use a 40m 33 foot monopole on 15m.
     
  3. ZL3GSL

    ZL3GSL Ham Member QRZ Page

    There's also the problem that the J-pole's quarterwave matching stub at 2m is not simultaneously a quarterwave matching stub at 70cm, so the SWR must be shocking at 70cm. Lossy coax might give "50 ohms" at the TX for 70 cm. ;)
     
  4. KE4FSL

    KE4FSL Ham Member QRZ Page

    Edison Fong made a very good dual band roll up jpole design. He has a paper about it here:
    http://snovalleyarc.org/pdf/roll up J Pole.pdf

    In the pdf is a version of the original 2 meter only model, as well as two versions of his dual band roll-ups. One for mounting inside a PVC pipe for either walking stick, or permanent use, and the other for roll-up use.
     
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