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Diamond 8900 Rear Tire Mount On Jeep, High VSWR @ VHF

Discussion in 'On the Road' started by KE8IXF, Mar 26, 2018.

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  1. KE8IXF

    KE8IXF Ham Member QRZ Page

    Just got a diamond 8900 and mounted it between my spare tire and tailgate on a bolt on mount. I had to drill out the mount a little bit, as well as drill 4 holes for the PL-259 flush mount connector, so it has a good ground. I confirmed it with a multimeter that it is grounded well.
    I tuned the 6m band first, as per the instructions, however i discovered that at the VHF band, my VSWR at 144MHz was 2.2:1 and at 148MHz was 3:1. Now i adjusted the tuning and got that VSWR to move slightly down but i ran out of room to shorten the antenna. It improved a little bit but I'm not sure how to get that VSWR down at VHF. All of the other bands sweep pretty well.
    I am using a Copper Mountain LNA to sweep.
  2. KC0LDH

    KC0LDH Premium Subscriber QRZ Page

    I don't know if anyone can truly diagnose your problem from their PC. Many good references on the forums, but it will come to you doing the leg work.

    I suggest some reading:

    Sounds like an RF vs. DC grounding issue. While you have a adequate DC ground, to RF your placement is quite questionable.
  3. W5HAS

    W5HAS Premium Subscriber QRZ Page

    I also have a Jeep and understand with the fiberglass top it's difficult to mount antennas anywhere else. I've had good luck tuning a firestick on 144Mhz and another firestick on 10 meters, as well as a 40 meter hamstick. However, I cannot get a 75 meter hamstick to work well back there, and I believe it is the longer load on that antenna interacting with the steel belt on the tire. Not much I can do about it short of removing the spare, and that's not a good option.
  4. W7EDC

    W7EDC XML Subscriber QRZ Page

    Note the factory tailgate is not grounded. Is it an add-on tire swing, or the factory third brake light mount... I am guessing it is a JK?

    Here is an older antenna JK thread... I think I jump in on page three

    jk 2m.jpg
    Last edited: Mar 29, 2018
    CRUISER177 likes this.
  5. KF5BCX

    KF5BCX Ham Member QRZ Page

    Wranglers are great, have had mine for 10 years and still going strong, just not the easiest for radios. See my QRZ page, right side of tailgate, same antenna with a trunk lid mount. I used heavy braid on both sides of tailgate to bond it and the antenna mount to the body, in addition to the doors, an extra one for the hood to the firewall and a spare threaded hole on the engine block, muffler to body and so forth. If you use the tailgate tire mount or stop light, I would run a heavy braid from the antenna mount to bonding braid for tailgate. There is room through the rear vent flap. Good luck! 73
  6. KE5PPH

    KE5PPH Ham Member QRZ Page

    use a mount like the one on the JK but put it on the hood next to the hinge.
  7. KD5RJZ

    KD5RJZ Ham Member QRZ Page

    I had the exact same antenna mounted to the aftermarket tire carrier on my CJ7 and had to add a ground as the hinge on the tire carrier wasnt helping the situation. Make sure the antenna is higher than the tailgate.

    I just bought a CJ6 with a metal roof and am very excited for my new ground plane lol.

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