unusual cb problem.

Discussion in 'CB Radio Forum' started by Ezrider_48501, Apr 2, 2011.

  1. Apr 2, 2011 #1
    Ezrider_48501

    Ezrider_48501 Road Train Member

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    I'm running a cheap cobra 19 compact radio in my gmc i started having trouble communicating on the road a couple weeks ago, the last couple days people were saying it sounded like i was out of channel. this is a bone stock radio with no tweeks or mods running barefoot, i figured for the price im probably better off buying another rather than trying to find a cb shop. i went to wal-mart and bought another one swaped them out and didn't get a response when. when calling out for a radio check but im a bit off the beaten path at the moment as well.

    i temporarily hooked my old radio up as a talk back with no antenna attached and the new one is doing the same as the last its bleeding into the two adjacent channels. one up and one down. i dont have a swr meater with me as im not near home. but it was tuned on the old radio. wondering if a antenna problem might be the cause. or if the receiver on the other radio is messed up as well even though when talking to other people on it, it seemed to receive ok.
     
    Ezrider_48501, Apr 2, 2011
    Ezrider_48501, Apr 2, 2011
    #1
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  3. Apr 2, 2011 #2
    Yup

    Yup Medium Load Member

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    grounding issue
     
    Yup, Apr 2, 2011
    Yup, Apr 2, 2011
    #2
  4. Apr 3, 2011 #3
    Ezrider_48501

    Ezrider_48501 Road Train Member

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    antenna or radio? ground

    i ran a new ground for the radio and it did seem to make a improvement. i need to re run all my wires for my cb, just don't have time at the moment. the antenna is a Wilson mag mount. i removed the antenna and whiped both surfaces clean and put it back on, it now seems to hardly bleed to the lower channel, a tiny bit of static, to the upper channel there is still some bled over but not nearly as bad, with both radio's on the same channel the transmision is much clearer than it was.

    i had the cb ran off some factory wiring i now have the ground to the chassis. i already planned on getting it wired properly soon, hopefully that will clean it the rest of the way up. is there anything else i should check now, also would it help to ground the radio chassis to the chassis of the truck as well.
     
    Ezrider_48501, Apr 3, 2011
    Ezrider_48501, Apr 3, 2011
    #3
  5. Apr 3, 2011 #4
    Turbo-T

    Turbo-T Road Train Member

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    I believe when you operate two CB's in real close range you may expereince some bleedover. I know on my base rig the antenna is about 20 + feet from where my mobile's antenna was, and once I had the mic to the base rig keyed up (was doing some testing) and could hear the transmission on the next channel on the mobile's radio.

    But yes, ground everything for noise reduction.
     
    Turbo-T, Apr 3, 2011
    Turbo-T, Apr 3, 2011
    #4
  7. Apr 3, 2011 #5
    Xcis

    Xcis Medium Load Member

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    Please do not operate a cb radio without hooking up either an antenna or a dummy load. You can really screw up the power transistors and make the radio a piece of junk.
    .
    If you are going to ground the antenna for RF (radio frequency) purposes, run short lengths of wire or the ground wire will act like a second antenna and screw up the antenna tuning proceedure. Run a short length of ground strap from one of the bolts that connects the door to the top of the door hinge and connect the other end to the top bolt that connects the top hinge to the door frame. It will look like you are shorting the door to the door frame bypassing the hinge.
    .
    This is not electrical grounding. It is RF grounding; that is different. Do not run a long wire from the antenna mount or door to the chassis.
    . Do run a short wire from door to door frame as I explained in the above paragraph. Then run a wire from the bottom of the door frame to the chassis if needed.
     
    Last edited: Apr 3, 2011
    Xcis, Apr 3, 2011
    Xcis, Apr 3, 2011
    #5
  8. Apr 3, 2011 #6
    Yup

    Yup Medium Load Member

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    do not run shielded wire for RF grounding purposes
     
    Yup, Apr 3, 2011
    Yup, Apr 3, 2011
    #6
  9. Apr 3, 2011 #7
    handlebar

    handlebar Heavy Load Member

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    OTOH, if you have a bunch of shielded wire lying around, use *just* the shield for your RF ground connections. The braid will have the increased surface area to carry RF more efficiently because of so-called "skin effect", in which the higher the frequency, the more the signal travels along the outermost portion of the conductor, rather than through the core of a wire.
     
    handlebar, Apr 3, 2011
    handlebar, Apr 3, 2011
    #7
    Yup Thanks this.
  10. Apr 3, 2011 #8
    Ezrider_48501

    Ezrider_48501 Road Train Member

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    the radio that did not have the antenna hooked up was never keyed up just had it to hear my own transmission.

    as far as the grounding if i am understanding you correctly you are saying to run wires from the doors to the chassis and from the chassis to the frame?
     
    Ezrider_48501, Apr 3, 2011
    Ezrider_48501, Apr 3, 2011
    #8
  11. Apr 3, 2011 #9
    Ezrider_48501

    Ezrider_48501 Road Train Member

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    also in a couple days im going to have a day or two down at home and i want to re-run my power wires for my cb, should i use positive and ground direct to the battery twisted together or 1 power wire from the battery and then ground to a near by place on the body.

    on a side not my radio seems to be working as it should now. i guess my now i have a second radio i can tinker with, i want to ad a rf gain and talk back to it.
     
    Last edited: Apr 3, 2011
    Ezrider_48501, Apr 3, 2011
    Ezrider_48501, Apr 3, 2011
    #9
  12. Apr 9, 2011 #10
    Xcis

    Xcis Medium Load Member

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    Okay, this is a long explanation that definitely applies when your SWR is 3.0 or higher. It also applies when tuning the antenna does not lower the SWR. Or, you have a strange problem that just defies solution.
    .
    Check the resistance between the antenna mount and the door. It should be zero. If not do the following: run a ground wire from the antenna mount to the door. Specifically, run the ground wire from the antenna mount. Connect the other end to the bolt that mounts the door to the top of the door hinge on door side. Recheck your SWR.
    .
    Check the resistance between the antenna mount and the door frame. This should also be zero. If not do the following: attach one end of the ground wire to the top bolt of the door hinge that connects the door to the door hinge. Attach the other end of the ground wire to the top bolt on the top door hinge that connects the door hinge to the door frame. This will look like you are directly wiring the door to the door frame by shorting or bypassing the the top door hinge.
    .Next, if you have two door hinges that connect the door to the door frame, you may need to do the following: run a short ground wire from the bottom of the top door hinge on the door frame side; to the top of the bottom door hinge on the door frame side.
    .Recheck your SWR.
    .
    Check the resistance between the antenna mount and the chassis. This should also be zero. If not run a short ground wire from the door frame to the chassis.
    .
    It is important that you use short lengths of ground wire. Avoid long lengths of ground wire as they will act like another antenna.
    .
    The purpose of all this is to interconnect the large metal surfaces of the truck into one large ground plane. This is RF (radio frequency) grounding. It has nothing whatsoever to do with electrical grounding.
    .
    .
    As a side note, the legal limit for a cb radio is 4 watts of power. All straight from the factory, stock out of the box, cb radios will put out approximately 3 watts of power. Spending more money gets you more features and a better (more prestigous) brand name. More money does not get you more power in a purely stock cb radio.
    .
    It is fairly rare to find a defective radio. Possible; just not likely. Most problems with cb radios are the peripherals -- antenna, coax, mike and faulty installation. Upon completion of the installation, I strongly suggest that everyone first get the SWR checked before using the radio. If the SWR is 3.0 or higher, a screwed up ground plane is the most likely the problem. If the SWR is between 1.1 and 1.5, you are good to go. If the SWR is higher than 1.5 but lower than 3.0, first try tuning your antenna. If that does not drop the SWR into the 1.1 to 1.5 range, check your ground plane by measuring the resistance between the antenna mount and the door, door frame and chassis.
     
    Last edited: Apr 9, 2011
    Xcis, Apr 9, 2011
    Xcis, Apr 9, 2011
    #10
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