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Cobra 29 LX High SWR Reading

Discussion in 'CB Radio Forum' started by Funjester, Mar 21, 2012.

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  1. Mar 21, 2012 #1
    Funjester

    Funjester Bobtail Member

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    Mar 17, 2012
    NJ
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    OK. I have this CB installed and I'm having a little issue getting a low SWR. Right now I have on ch 1 1.5 and on 40 1.8
    If I tune down the firestik II i have by taking out the adjustment screw I get a 1.9 on all ch.. How can i get the SWR lower???
    I have the mount grounded, I have the bottom of where the stud and coax go in grounded down. I have checked and rechecked everything and can't figure it out.
    I have to coax run along the roll bars to the cb. I trimed off the extra coax so there is no rolls and no kinks.. I grounded the mount to the back of the tail lights with a 12 gauge wire. I grounded down where the screws go into the mount and thats where i put the extra ground. I put an ohms meter on the stud with the coax disconected and got the proper readings. I checked the coax and it has not been broken....

    Any Thoughts...???

    4' Firestik II FS Series Tunable tip 900 watts
    Wilson CB Coax with FME & Boot - 18' RG-8X (Premium Single)
     

    Attached Files:

    Funjester, Mar 21, 2012
    Funjester, Mar 21, 2012
    #1
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  3. Mar 21, 2012 #2
    jessejamesdallas

    jessejamesdallas Road Train Member

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    Where do you have your antenna mounted...and what is this on?

    It "could be" the antenna is too close to the body of whatever you have it mounted on, in which case that maybe as good as your going to get tuning...It could also be because your using a short antenna that may not tune as well as a taller one in the same location...

    Your installation going by the pictures tho looks fine...If the antenna was on the roof...It would probably tune allot better.
     
    jessejamesdallas, Mar 21, 2012
    jessejamesdallas, Mar 21, 2012
    #2
  4. Mar 21, 2012 #3
    Funjester

    Funjester Bobtail Member

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    Mar 17, 2012
    NJ
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    It's mounted on the spare tire mount of a jeep.
    All the swr readings say it should be shorter. If I take the adjusting screw out it levels off at like a 2.0...
    I just can't figure this out..
     
    Funjester, Mar 21, 2012
    Funjester, Mar 21, 2012
    #3
  5. Mar 21, 2012 #4
    jessejamesdallas

    jessejamesdallas Road Train Member

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    But probably half of the antenna is right up next to the back of the Jeep...

    One thing you can try, which may help, is to run some ground "straps" off the tire carrier and back door to the frame...Use flat ground braid and not round wire for this...you can use old coax for ground braid...Just strip off the outer plastic jacket, and pull out the center conductor wire, and use the ground braid...Just be sure to clean off any paint or rusty dirt before mounting the ground strap so to get a good connection...You can use self-taping screws to mount the strap.

    Or...try a different antenna...Lots of guys run 102" whips mounted on Jeeps like you have yours and get good readings.
     
    jessejamesdallas, Mar 21, 2012
    jessejamesdallas, Mar 21, 2012
    #4
  7. Mar 22, 2012 #5
    kc0iv

    kc0iv Light Load Member

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    If you sweep the freq SWR will indeed show the resonance of the antenna.

    When a 50 ohm resistor is used as a dummy load line length, VF, coax type doesn't matter.

    Leon
    (kc0iv)
     
    kc0iv, Mar 22, 2012
    kc0iv, Mar 22, 2012
    #5
  8. Mar 22, 2012 #6
    rollingradios

    rollingradios Light Load Member

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    Mar 9, 2012
    Richmond, Va
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    Funjester,
    On some installations the available ground plane simply doesn't suit a practical antenna. In your case, 1.5 on ch1 and 1.8 on ch40 I would let it ride.
     
    rollingradios, Mar 22, 2012
    rollingradios, Mar 22, 2012
    #6
  9. Mar 22, 2012 #7
    Funjester

    Funjester Bobtail Member

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    Mar 17, 2012
    NJ
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    OK added the braided ground but only had enough to go from the tub to the tailgait.. scraped some paint off the mount and the tire carrier. checked everything for ground and its perfect..
    Now I have a swr of 2 on ch 40.. so its going in the wrong direction..

    Next idea???

    ?If I put a 102" wip on it will even work? I have a 4' on it and its saying to shorten it..
     

    Attached Files:

    Funjester, Mar 22, 2012
    Funjester, Mar 22, 2012
    #7
  10. Mar 22, 2012 #8
    scoobydoojr

    scoobydoojr Bobtail Member

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    Mar 22, 2012
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    how long is your coax? I've had best luck with 12' of rg-58 and 14'7" of rg-8. then i check swr at antenna and at radio with meter .
     
    scoobydoojr, Mar 22, 2012
    scoobydoojr, Mar 22, 2012
    #8
  11. Mar 22, 2012 #9
    Funjester

    Funjester Bobtail Member

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    Mar 17, 2012
    NJ
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    I started with 18' and since have cut about 2 1/2 feet off.. I'll try swr at antenna..
     
    Funjester, Mar 22, 2012
    Funjester, Mar 22, 2012
    #9
  12. Mar 22, 2012 #10
    windsmith

    windsmith Road Train Member

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    You couldn't be more wrong. I won't bother explaining, since your previous posts demonstrate that you've chosen not to educate yourself about RF therefore the explanation would be wasted.

    To the OP:

    Here's a document outlining how to install and tune the antenna. Note that you may need a 'no ground plane' kit because of where you're choosing to mount it on your vehicle.

    Also, see if you can get a 'pre-made' length of coax with connectors on each end. This will eliminate any possible errors that you may have made when you installed the connectors.
     
    windsmith, Mar 22, 2012
    windsmith, Mar 22, 2012
    #10
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