Mag-mount or J-Pole

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K6DEA, Mar 13, 2016.

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  1. K6DEA

    K6DEA Ham Member QRZ Page

    I live in a down stairs condo and have a small 10x10 porch. There is not much coverage and need to keep the antenna as transparent as possible due to HOA Restrictions. I have been using a All metal bar stool and mag net mount with a small dual band mobile comet antenna and it works well. Switching to a big 5/8 mobile (sbb-5) antenna does not give me the reception the smaller antenna gives. I also have a big copper J pole I built and tried using this but reception is spotty for certain repeaters on UHF and my Primary band is UHF for now. I originally though of mounting the J pole on the bar stool ( to give it elevation) and camo it with fake plants but since the J pole sucks i am unsure what to do, is it possible i am mounting the J-Pole incorrectly? I was told this J pole is a NO GROUND design.

    Any one have any ideas on what I can do here? I have photos of each antenna mounted and can post pics of needed...
     
  2. K8JD

    K8JD Ham Member QRZ Page

    From what I can see the Comet SBB5 IS a small dual band antenna, what did you have originally ? Just an 19-20 inch whip ????
    UHF can have some tricky reflections and multi path problems if your antenna is not up way above the roofline. I have a ten ft tall multi dipole vertical array for 440 MHz on my roof and still can have some noisy reception of local repeaters, 20-30 miles away.
     
    Last edited: Mar 13, 2016
  3. AG6QR

    AG6QR Premium Subscriber QRZ Page

    A 2 meter J-pole won't work well for UHF. You can get a low SWR, and it will radiate, but the radiating element is a half wave at 2m, which is 3/2 wave at 70cm. So it will have three lobes in the pattern, one horizontal, one about 45degrees up, and one about 45 degrees down. There will be strong nulls between the lobes. The lobes that radiate up and down don't do much good for you, but they rob your power.

    If you're only working UHF, you're better off scaling the J-pole down to UHF size. Build it about 1/3 the size of the 2 meter plans.

    There are, of course, many other options besides a J-pole. This is just an explanation of why a 2m J-pole isn't a great performer on UHF.
     
  4. K6DEA

    K6DEA Ham Member QRZ Page

    Sorry I wasn't specific about the antenna I'm using now, it is a Comet SS680SB.

    The j-pole was built a long time ago, I don't have the tools to rebuild or build another. I'm on a budget and can't get too wild with spending money. If there is another antenna out there that may yield better results and not kill my bank account I will consider it.
     
  5. K6FNI

    K6FNI XML Subscriber QRZ Page

    I have an Arrow J-pole antenna mounted on a pipe that is secured to my deck railing and nobody is aware that it's there because it looks like a collapsed market umbrella.

    The supporting PVC pipe extends about 6 feet above the deck railing and the whole thing is covered by the market umbrella cover.

    It works well for me on 2 meters.

    Robert, K6FNI
     
  6. AK5B

    AK5B Ham Member QRZ Page

    What about a standard 1/4 wave ground plane made with five pieces of wire and a SO-239 panel mount? If you're only on UHF then one about 8.5" tall would be exactly what you need and should be very easy to conceal or camouflage. BTw, a 19" version would work for 2M/70cm, too.
     
  7. NM9K

    NM9K Ham Member QRZ Page

    That's what I was going to suggest. My 1/4 wave 2m antenna on my pickup works fine on 440. The same antenna is $18 on Amazon; a similar antenna with a UHF connector would probably be even cheaper. Add some radials and you're good to go.
     
  8. W7SJT

    W7SJT Ham Member QRZ Page

    Check out K9JEB. He makes a dual band 2m/70cm J-pole and sells it for $25. John also pretunes them for low SWR on 2m and 70cm, and they are very sturdy - built out of aluminum rod and aluminum angle. It looks identical to the Diamond J-pole that they sell for $50. Connect up the coax and go - plug & play. You can't build one for what he sells them for. I have one of John's antennas and it works great - I can hit the all the local repeaters using 5 watts and a HT if I have to and the most often used repeater is 25 miles away over hilly terrain in the Seattle area. I have my j-pole mounted on the front upper deck railing of the house on a short pole and my wife didn't even notice it until I pointed it out to her. For stealth mode you can paint them (mine is unpainted) and it won't affect the performance.
    (Also, I have no financial interest in what John sells, just sharing info about a great antenna)
     
  9. WA7DU

    WA7DU Ham Member QRZ Page

    Hmmmmm. Did you ever wonder about the coincidence that J-pole and the word "junk" both start with the letter J ?

    The reason that your mobile antennas do not perform better is that they are designed to have a ground plane (in the form of the an automobile's metal roof). Without that ground plane, half of your antenna system is missing.

    You might try to "simulate" the missing metal roof with a sheet of metal--even a large cookie sheet might help. Absent a cookie sheet, you might try a piece of metal mesh screen like the cage material used to make a gerbil cage.

    The next challenge you might face is antenna height. UHF needs a line-of-sight path to the antennas of other stations you are trying to contact. Most of the time, height is the most important aspect of getting line-of-sight access.

    If the "simulated" automobile roof doesn't improve either of your mobile antennas, build the 1/4-wave ground plane antenna suggested in an earlier post--it is the one built around an SO-239 connector. Use coat hanger wire for the radiator and the four ground plane wires. The only thing you may have to buy is the SO-239; it's a couple of bucks.
     
    Last edited: Mar 15, 2016
    AK5B likes this.
  10. K6DEA

    K6DEA Ham Member QRZ Page

    I should go surf around some thrift shops and see if I can find something big enough to put that mag mount on.
    I wonder if a oven rack will work...sounds super cheap and "ghetto"
     

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