The j-pole antenna is fixed...

Discussion in 'Amateur Radio News' started by KX4O, Jul 9, 2020.

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  1. WB4YZ

    WB4YZ Ham Member QRZ Page

    Groovy Mahn...Real Groovy
     
  2. ZL1PDT

    ZL1PDT Ham Member QRZ Page

    Hi All.
    Me I do prefer the Slim Jim easy and short that a J-pole and is adjustable for for where you want or need to
    oparate does not fall all over and less wind and storm damage have used for many years and no maintance free fpo more than
    20 years look here http://www.hamuniverse.com/slimjim.html it just keep working build 1 and build with good stuff ever in to pvc tube with 300 ohm tape,
    73,
    Pieter
    ZL 1 PDT / ex ZS1PDT
     
  3. K1LNC

    K1LNC Ham Member QRZ Page

    This
     
  4. K1LNC

    K1LNC Ham Member QRZ Page

    Years ago a friend's vhf marine antenna took a lightning hit...at her home in The Bahamas. She wanted to replace it...and damn near fainted when she saw what a new one costs. I built her a "temp" replacement ground plane using an SO239 coax panel connector and some copper welding rod. Whole thing took about 30 minutes and cost about $5.00. Hoisted it up on a PVC pipe...fed it with RG-8 coax...and...presto. I read with some amusement in QST and elsewhere all these antennas to be built...complicated....hard to get tuned right. KISS....it works.
     
  5. PA0MHS

    PA0MHS XML Subscriber QRZ Page

    I would never replace a 1/2 wave VHF marine antenna with a 1/4 wave groundplane. Your life may depend on it. A 1/2 wave radiates nearly horizontal while a 1/4 wave GP radiates some 30 degrees upwards, giving you much less range.
    I recently built a 1/4 wave GP for 23cm just for fun and I noticed that I could only work a specific repeater 20 miles away when I tilted the antenna downwards in the direction of the repeater. Vertically, I could not reach it.
     
  6. N3HGB

    N3HGB Ham Member QRZ Page

    https://www.amazon.com/Shakespeare-...ords=marine+VHF+antenna&qid=1595345917&sr=8-4
    Just cough up the $50 and be safe!
     
    PA0MHS likes this.
  7. KE4IKY

    KE4IKY Ham Member QRZ Page

    If a 1/2 wave has more gain than a 1/4 wave due to a narrower vertical pattern, wouldn't the boat healing reduce the effectiveness of the 1/2 wave?
    Thanks
    Joel
     
  8. KX4O

    KX4O Ham Member QRZ Page

    That's a good question especially for single hull sail boats. I'd say the patterns of both are so broad and similar that this won't matter for all, but the most serious angles. Here is a comparison (measured) of two 1/4 wave approaches with a J (half-wave)...
    [​IMG]
    I think the takeaway here is boat healing, while an important consideration, won't be a big deal until you have some collinear gain of some sort. Here's an example where antenna tilt begins to matter. Your question is perfectly reasonable. I think we are reasonably safe with either a 1/4 or 1/2 wave vertical antenna with respect to boat healing.
     
  9. KE4IKY

    KE4IKY Ham Member QRZ Page

    Thanks.

    In your reference, it looks like about 30 degrees (or so) angle of heel, there would be nulls. I'd love to see the real effect on range of different antennas on sailboats, given that height is probably the dominant factor in range and a larger antenna puts weight at the top of a mast and affects the boat itself.

    For example compare a duckie that's mounted just under the masthead light (lets say 30' to 45', and a 5/8 wave mounted 6' above the water (with either a gimbel mount or hard mounted), at 30 degrees of heel or so (which would only affect the non gimbel-ed antennas).

    Not that any of this matters to me, I'm more of a canoe person, but it's a god thought exercise.

    Thanks
    Joel
     
  10. AC7LX

    AC7LX Ham Member QRZ Page

    Never been a fan of this design to begin with, less so of the occasionally ludicrous performance claims.

    That said, it seems like someone didn't research this well when it comes to patents. As mentioned by others, decoupling of a J-Pole isn't anything new, nor is feeding the feed-line inside the copper. But then we seem to be talking about a government agency so... whatever.

    :(
     

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