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Mobile antenna grounding...

Discussion in 'General CB Services Discussion' started by BammBamm, Jan 9, 2018.

  1. BammBamm

    BammBamm Chicago's mudduck.....173 on the southside.

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    O.K. I had a question thrown at me that I couldn't answer and it bothers me..Here goes...My Coworker is just getting into 11 meter and I helped him install a old 29 ltd and 102" whip on his truck. I ran a ground from radio case to chassis as I always do, He then asked why I did that when the shield of the coax is grounding the same way at the antenna mount? Then I started wondering....If I am doing this with my wilson 1000 magnetic will I see a difference in hard mounting it? Thanks again to all of you for sharing your knowledge with us all!


     

  2. DainBramage

    DainBramage Well-Known Member

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    mag mounts do not provide a good ground to your vehicles chassis. add the extra ground connection.
     
  3. BammBamm

    BammBamm Chicago's mudduck.....173 on the southside.

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    So...If I do this would hard mounting it make a difference instead on a wilson 1000 mag mount?
     
  4. Robb

    Robb Yup

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    I use nothing but mag mounts. They work thru 'capacitive coupling' to the body sheet metal. Sure, solid mounts are better; but mag mounts will work just fine. If running power; then that is another story.

    Running braided copper wire is the way sheet metal surfaces (doors, hood, trunk, fenders, frame) and even the exhaust pipe will create extra ground plane surfaces. The radio is already grounded to the battery thru the power cord, so you do not need to run an extra wire to ground.
     
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  5. Road Squawker

    Road Squawker Sr. Member

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  6. Road Squawker

    Road Squawker Sr. Member

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    We were talking about RF ground, not elect. ground.

    doors, hoods, ect are not grounded to the chassis, anything on a hinge has a poor elec. connection.
    put a VOM across the hinge and see for yourself.

    Exhaust systems are not grounded at all, they "float" on insulators.

    Believe it or not, even engine blocks are not grounded.
     
  7. 9C1Driver

    9C1Driver Sr. Member

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    Agreed. Have been running mag mounts on company cars for 28 years now. I even use a Silver Streak 175 or Texas Star 250 run straight to the battery with no problems.
     
  8. Robb

    Robb Yup

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    Really? The engine starter uses one lead from the positive battery and is engaged thru a relay to make the starter spin. The engine is grounded to the battery negative post so the starter will spin/completing that circuit. Usually, a large gauge wire goes from the battery to the frame and another comes from the frame to the engine, since most vehicles being mfd are uni-body construction. So they are all grounded to the battery directly or indirectly. Maybe I misunderstood your point?
     
    #8 Robb, Jan 10, 2018
    Last edited: Jan 10, 2018
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  9. BammBamm

    BammBamm Chicago's mudduck.....173 on the southside.

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    Ok. I understand the answer given but I'm still confused..If the ground side of the coax is directly connected to the chassis of the radio at the antenna jack on the back of the radio and I then use a magnetic antenna but run a large gauge wire from radio chassis to ground would it be of any improvement to drill a hole and hard mount the antenna?
     
  10. W2EKG

    W2EKG 201 Mike Action

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    I got a follup Question. I'm using a little will, tried three different SSB Radios(10ga to the battery), grounded the radio to the seatbolt. Issue, audio unintelligible(thinking reflect). Thinking of changing to a diamond k-400(+braid), and a Firestik, will be that solve my problem?
     
  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    It is grounded DC wise but it is not a real good ground RF wise. I have put an ohmmeter across door/hood/trunk hinges before and you could see the resistance change as you swung the door open and closed. I even had a trunk lid show completely open when it was almost closed. I had to install a ground strap on either side of the trunk to ensure continuity. What led me too this problem was an intermittent high SWR on my trunk mounted HF antenna. Everything look good DC wise until I started to push on the trunk lid.
     
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  12. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I would not ground to the seat bolt or any part of the body. This can cause a ground loop which can pick up noise like an antenna. I would run a 10ga ground to the battery to go along with the 10ga positive. Also make sure the cord that plugs into the radio is big enough to supply the power that is needed. The cheap 16ga cords are not big enough even for 4w output in my opinion. I favor the workman 12ga for most radios. Hope this helps.
     
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  13. M0GVZ

    M0GVZ Sr. Member

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    The RF ground MUST START WHERE THE COAX BRAID ENDS AT THE ANTENNA END.

    Putting straps between the radio and the body does not create a RF ground, mounting the radio bracket to metal of the vehicle body doesn't give you a RF ground, it does not make up for a poor one. You still have noise, you still have all the issues from common mode RFI.

    Hard mounting will improve it and you'll see the improvement by the fact you need to shorten the antenna which is an indication of a better RF ground. You also then want to do plenty of bonding as described in the bonding section at www.k0bg.com. You will find that when you've done that and improved the flow of RF over the vehicle body that you need to shorten the antenna even more.

    DO NOT USE WIRE for RF ground. RF travels over the surface of a conductor, not through it so surface area counts. To get the same conductivity as flattened RG213 braid you'd need to use 0000 gauge wire.
     
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  14. OldTech03

    OldTech03 Active Member

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    Finally someone got it right I didn't have time to respond to this but I can tell you as someone that has installed many hundreds of systems in Tractor trailers, SUV's, Cars, and Pickups going back to the Positive ground days it has always been an issue from one truck to another from one year to another etc, I can say that I invested in 50' rolls of copper strap this method works and yes it is more time intensive but worth it. Another thing to remember when strapping be sure to keep the lengths of strap or whatever you use short and different lengths "another words break up the ground strap if you are going from a mirror to a door and the door is metal make a connection at the top of the door and then at the bottom of the door to the jam instead of running a continuous strap or wire as this can sometimes be seen as an un-tuned element instead of a ground. Also, Put as many right angle bends in the strap or wire as you can. Again be sure all connections are to bare metal and all connections coated with clear silicone sealer after done. Ok, I have rattled on enough I simply elaborated on MOGVZ's post so I hope he is Ok with that.

    OldTEch03
     
    #14 OldTech03, Jan 10, 2018
    Last edited: Jan 10, 2018
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  15. Robb

    Robb Yup

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    ANS: No.
    Don't confuse electrical ground with RF ground; two different animals.

    Just mount the mag mount on the roof, adjust for best SWR on CH 20, and you are done.
     
    #15 Robb, Jan 10, 2018
    Last edited: Jan 11, 2018
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