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What does it mean... (SWR issues content)

Discussion in 'CB Radio Forum' started by volvo244t, Mar 29, 2013.

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  1. Mar 29, 2013 #1
    volvo244t

    volvo244t Road Train Member

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    Bettendorf, IA
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    ...when my SWR is extremely high, almost pegging, until I simultaneously touch both the mount and the stud/base of the antenna (4.5ft Francis) at which point it plummets to ~1.3?

    '10 International ProStar, mirror mount, top bracket. Shoulder washer is above mount, between mount and antenna stud. Mount is grounded to one of the bolts that holds the mirror bracket on. Haven't yet grounded the door to the body. 18 feet of Mini-8 coax, excess is NOT coiled into a circle. Antenna is turned forward ~30 degrees to get it away from the body of the truck. Galaxy DX-939 radio.

    I'm completely at a loss here.
     
    volvo244t, Mar 29, 2013
    volvo244t, Mar 29, 2013
    #1
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  3. Mar 30, 2013 #2
    Turbo-T

    Turbo-T Road Train Member

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    Sounds like a ground problem

    BTW it's not a good idea to touch the antenna while transmitting.
     
    Turbo-T, Mar 30, 2013
    Turbo-T, Mar 30, 2013
    #2
  4. Mar 30, 2013 #3
    Acm

    Acm Bobtail Member

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    Feb 28, 2013
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    Hmm,I never have touched and looked to see if a difference,but if it is high reading,all the normal stuff.are you sure ant is good?I have seen the cheaper shouldered studs cause problems,are your ends soldered or crimped?corrosion?
     
    Acm, Mar 30, 2013
    Acm, Mar 30, 2013
    #3
  5. Mar 30, 2013 #4
    n9mxq

    n9mxq Light Load Member

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    Aug 13, 2010
    Belvidere, IL
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    It means your body is adding to the electrical length of the antenna. Not a wise choice, as mentioned before.. On a stock radio, not much to worry about, but try that with an amp inline, and you'll find out what an RF burn feels like. I got nailed helping a friend, he didn't realize I was in contact with the antenna..

    I would ground the door to the body, and stand the antenna straight up. Anyone who believes you do better with a tilt is full of it. It will change your radiation pattern.
     
    n9mxq, Mar 30, 2013
    n9mxq, Mar 30, 2013
    #4
  7. Mar 30, 2013 #5
    mike5511

    mike5511 Road Train Member

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    It will change your "coolness factor" too!:D
     
    mike5511, Mar 30, 2013
    mike5511, Mar 30, 2013
    #5
  8. Mar 30, 2013 #6
    EZ Money

    EZ Money Road Train Member

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    Oct 27, 2010
    The East Side Gang,Charlotte,NC.
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    lol! yep! I see so many trucks that have them about horizontal...
    Also so many that have 2 or more antennas on the same mirror...i bet they never checked SWR.....
     
    EZ Money, Mar 30, 2013
    EZ Money, Mar 30, 2013
    #6
    mike5511 Thanks this.
  9. Mar 31, 2013 #7
    RockinChair

    RockinChair Road Train Member

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    CC, TX
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    When you touch the stud & the mount, your body is becoming the pathway to ground.


    You mentioned that the nylon washer is between the stud and the top of the mount, as it should be. Is there something on the underside of the moumt that is keeping the metal on the PL-259 from making contact with the mount?
     
    RockinChair, Mar 31, 2013
    RockinChair, Mar 31, 2013
    #7
  10. Mar 31, 2013 #8
    volvo244t

    volvo244t Road Train Member

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    Jun 24, 2010
    Bettendorf, IA
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    I am not in the truck at the moment, but when I get back to the truck, I will double-check. I don't believe there is.
     
    volvo244t, Mar 31, 2013
    volvo244t, Mar 31, 2013
    #8
  11. Mar 31, 2013 #9
    volvo244t

    volvo244t Road Train Member

    1,779
    1,779
    Jun 24, 2010
    Bettendorf, IA
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    Is that why, in my old setup, the forward tilt resulted in a .5-.6 reduction in SWR vs. straight up? I tried many different angles, from straight up to 45 degrees forward. Best SWR was at around 30 degrees forward.
     
    volvo244t, Mar 31, 2013
    volvo244t, Mar 31, 2013
    #9
  12. Mar 31, 2013 #10
    n9mxq

    n9mxq Light Load Member

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    Aug 13, 2010
    Belvidere, IL
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    Changing angle changes the distance from other reflective objects. It also changes the radiation pattern. instead of going straight out in all directions (except those blocked by the vehicle body), tilting the antenna makes the signal bounce off the road in front of you, and pass over people behind you.

    Sure, after a certain distance it's all irrelevant, but in the distances that matter on the road it could well make a difference. I've never tilted an antenna, and never will. They're designed to work in a vertical position, and that's where they work best. If they were meant to be tilted, the installation directions would specify the optimum degree of tilt.
     
    n9mxq, Mar 31, 2013
    n9mxq, Mar 31, 2013
    #10
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