If I reversed polarity...

Discussion in 'CB Radio Forum' started by Treefork, Mar 12, 2012.

  1. Treefork

    Treefork Road Train Member

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    On my cb, could that cause it to receive but not transmit? Or would it fry everything?

    My Cobra 148GTL (1993) has stopped transmitting since I moved it into this 2013 Prostar. The wire colors are backwards (green is hot, white is ground) and the first time I hooked it up I think I had it the other way for a brief time. I put a new cb in and it works fine. Also changed the battery on my mic on the 148. Also, if it was caused by reverse polarity, can the cb be repaired?
     
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  3. country29

    country29 Medium Load Member

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    it should have a protection diode inside the radio, it can be replaced at a good shop or if you are into electronics you can do it yourself. should be able to get it fixed for $30 or less depending on what radio shop you go to.
     
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  4. WA4GCH

    WA4GCH Road Train Member

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    There is on most radios a reverse protection diode. IF YOU HAD A FUSE in line with the radio power cord you should have blown the fuse other wise you could have blown the foil off the board going to l401 and the diode ...
     
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  5. popmartian

    popmartian Road Train Member

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    All metals are composed of positively charged atoms immersed in a sea of movable electrons. When an electric current is created within a solid copper wire, the "electron sea" moves forward, but the protons within the positive atoms of copper do not.

    In other words, electric current (negative charged particles called electrons)flow through a circuit from the ground to the hot lead. The inline fuse is to provide overcurrent protection, of either the load or source circuit, Thus the need for only one fuse on the power supply.

    By reversing the polarity, the cb would not function.
     
    Last edited: Mar 13, 2012
  6. Crusty

    Crusty <b>Just Plain Crusty</b>

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    What he said. I lost one radio due to reverse polarity. Fusing both wires is the only way to go!
     
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  7. popmartian

    popmartian Road Train Member

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    What about the antenna ground......It also loops directly to the battery, when the antenna is connected to the CB, current is flowing from the battery to the CB. But with the switch off the circuit is broken. Before connecting any power lines, the user should test the leads with a volt/ohm meter to determine which one is ground which one is hot. Yea, the hard case way would be to purchase a second fuse holder, install it, and then hope you properly connected the positive to the positive and the negative to the negative....again I say not needed.
     
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  8. M818

    M818 Light Load Member

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    Many "CB radios" have the + and the - isolated from their chassis. The chassis is connected to the - side (negative wire) through a capacitor and that is what grounds it for the radio waves. This isolates the DC voltage from your battery from the "radio's" case. Therefore as long as the polarity of the power wires to the "radio" is correct, grounding the "radio's" case as well as the antenna, etc. is fine.

    If the set has no such isolation then the sparks may fly in a positive ground truck. This goes for "linears" and the other crap too.

    You can check with an Ohm meter from the - lead of the "radio" to its case to see if it is isolated or not.

    What genius came up with a positive ground truck anyway? just had to be different..
     
  9. Big_m

    Big_m Heavy Load Member

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    I don't think that any trucks made in last 20 years had a negative ground.
     
  10. kc0iv

    kc0iv Light Load Member

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    I think you mean positive ground .


    Leon
    (kc0iv)
     
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  11. popmartian

    popmartian Road Train Member

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    I followed the links and could not find a discussion on ground fuses included. the issue of ground loops, and ground straps, RFI, and SWR was interesting. The author suggested by-passing any factory power connection, IE cigarette lighter and attach power leads directly to the battery. One last note. DC grounding and Chokes were discussed regarding Mobile CB's. Thanks for the link.

    On Big Rigs, The factory installed power and antenna wires are internally grounded to the chassis, for one reason. a common ground. But as the article in your link advised, RF and DC grounds are separate issues. Next, the truck becomes a capacitor between between the the ground plane (earth) terra firma.

    Positive ground: using postive grounds in foreign made vehicles is not the same as reversing polarity in a Class 8 heavy duty CMV. that would be a different topic.

    I guess we will agree to dis-agree on why two fuses are better than one, LOL...

    Lastly, The "Big Radio" would require professional install, But a cobra 29ltd CB for the average joe driving a Big Truck is so easy to install even a cave-man could do it.

    [​IMG]
     
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