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Voltage issues at battery when I transmit. Battery rises to 13.67

Discussion in 'CB Radio Forum' started by C.B. HAWK, Dec 7, 2018.

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  1. Dec 7, 2018 #1
    C.B. HAWK

    C.B. HAWK Bobtail Member

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    Hi All

    I'm running a Cobra mobile set as a base unit, powered by a 12v battery. Static voltage 12.65. When I transmit the voltage at the battery rises to 13.67. My S.W.R. is slightly over 1:1. Any ideas on this voltage thing?


    C.B. Hawk
     
    C.B. HAWK, Dec 7, 2018
    C.B. HAWK, Dec 7, 2018
    #1
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  3. Dec 7, 2018 #2
    Ridgeline

    Ridgeline Road Train Member

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    It isn't rising, you have rf being fed back into the DC circuit or the volt meter is picking up RF from the antenna that is making it look like there is an added voltage.

    There is something called a Common Current Mode issue that happens with radio antenna system, so the first thing that has to be asked is what are you using for an antenna and how old is your coax?
     
    Ridgeline, Dec 7, 2018
    Ridgeline, Dec 7, 2018
    #2
    handlebar, Meteorgray, rabbiporkchop and 1 other person Thank this.
  4. Dec 7, 2018 #3
    C.B. HAWK

    C.B. HAWK Bobtail Member

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    Hi Using a Wilson Silver Load 4' and my coax is two months old. Digital meter.


    Thanks. The Hawk.
     
    C.B. HAWK, Dec 7, 2018
    C.B. HAWK, Dec 7, 2018
    #3
  5. Dec 7, 2018 #4
    C.B. HAWK

    C.B. HAWK Bobtail Member

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    Dec 7, 2018
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    Hi Using a Wilson Silver load 4" coax two months old, digital meter.



    Thanks. The Hawk.
     
    C.B. HAWK, Dec 7, 2018
    C.B. HAWK, Dec 7, 2018
    #4
  7. Dec 7, 2018 #5
    jessejamesdallas

    jessejamesdallas Road Train Member

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    Like Ridgeline said...It's probably just stray RF messing with the digital volt meter.

    Do you have this battery hooked up to some kind of charger? If so, it could just be the charger sensing a voltage drop when the radio is keyed, and it's sending a charge back to the battery, sorta like the way a alternator does...
     
    jessejamesdallas, Dec 7, 2018
    jessejamesdallas, Dec 7, 2018
    #5
    Meteorgray Thanks this.
  8. Dec 8, 2018 #6
    Ridgeline

    Ridgeline Road Train Member

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    Just wondering if you are using the antenna near the radio like on a cookie sheet or mounted somewhere near the radio and not grounding it to the actual ground.

    The reason I ask is that if you just stick an antenna anywhere without a ground, the rf feeds back to the radio to create an rf ground and this is where that common mode thing is created.
     
    Ridgeline, Dec 8, 2018
    Ridgeline, Dec 8, 2018
    #6
    Meteorgray and AModelCat Thank this.
  9. Dec 8, 2018 #7
    C.B. HAWK

    C.B. HAWK Bobtail Member

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    Good theory, I didn't think of that one. No, just a battery by itself.


    Thanks. The Hawk.
     
    C.B. HAWK, Dec 8, 2018
    C.B. HAWK, Dec 8, 2018
    #7
  10. Dec 8, 2018 #8
    C.B. HAWK

    C.B. HAWK Bobtail Member

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    Hi All. Using this Silverload on my garage roof I have made up four 4' X 3/16" steel rods as ground radials and am using an antenna tuner. Radials connected to radio set chassis and on to the local water pipe. The battery is not "grounded' as would be the case in a car. I'll try connecting the battery negative to the water pipe and we'll see what happens.


    More Thanks. The Hawk.
     
    C.B. HAWK, Dec 8, 2018
    C.B. HAWK, Dec 8, 2018
    #8
  11. Dec 8, 2018 #9
    Ridgeline

    Ridgeline Road Train Member

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    Yep that's the problem. Ground the radio and the antenna.
     
    Ridgeline, Dec 8, 2018
    Ridgeline, Dec 8, 2018
    #9
    Meteorgray Thanks this.
  12. Dec 9, 2018 #10
    C.B. HAWK

    C.B. HAWK Bobtail Member

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    Further observations. The internals of the set are not connected to the metal case of set. With the battery connected only to the + and - wires the voltage rises from 12.32 v to 14.32 v when transmitting. When I connect the negative of the battery to radio case it only rise to 12.77. How come?
     
    C.B. HAWK, Dec 9, 2018
    C.B. HAWK, Dec 9, 2018
    #10
    bigguns Thanks this.
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