CB Antenna Ground

Discussion in 'General RVing' started by Sober0782, Dec 18, 2005.

  1. Sober0782

    Sober0782 New Member

    I have a CB Antenna that needs to be grounded for a proper match. Problem is that with the fibergalss sides and no metal near the antenna mount where do I ground it ? Any suggestions, the antenna is mounted just outside the Drivers window at roof level on a Coronado (Fleetwood) Class A. Any suggestions welcomed.
    thanks, Ed Riverbank Ca. :)
  2. Krazeehorse

    Krazeehorse New Member

    CB Antenna Ground

    Is the top of the antenna just at roof level or is most of the antenna above the coach? If the top of the antenna is just flush with the roof then that is the cause of your high SWR. Of course if the antenna is up above the roof much on a motorhome the trees will take care of it. The antenna itself should be getting a ground throught the braid of the coax. Check your mount with a continuity tester. So if reflection is the problem then you might have to try a different location or a different antenna. Krazee
  3. TexasClodhopper

    TexasClodhopper Senior Member

    CB Antenna Ground

    You first have to determine if you are talking about DC "ground" or the RF ground plane. You don't "get out" because you have a DC connection through the coaxial cable shield/braid. After all, your coaxial cable could be connected perfectly to your antenna while you dragged the antenna behind your MH on the ground! Obviously, you wouldn't be "getting out" in that case.

    Without getting into RF theories, your best bet to "get out" (with fiberglass sides/top) would be to look at antenna designs for marine applications or possibly one designed for Corvettes.

    Does CB "work" more than a quarter mile, anyway? Why worry about SWR? (From a practical standpoint.)
  4. John Harrelson

    John Harrelson New Member

    CB Antenna Ground

    Hi Sober,

    The coax cable has a "Force Field" around it in the form of a braided shield. This braided shield does two things, it helps prevent the radio signal from bleeding out of the cable and interrupting other electronic equipment near it ... and the braided shield provides a positive ground between radio and antenna needed for the radio to work properly.

    But judging from your post, its not the ground thats causing your problem ... it sounds like you are not getting a proper "match" for the antenna and the radio, commonly called "Standing Wave" .. This can be caused by one (or all) of three things...

    #1.. the antenna shaft is not of the proper length. (metal antennas only)
    #2.. The coax cable not of the proper length.
    #3.. the coax braid is in contact with the antenna shaft.

    Just for information only,... for a CB antenna to work at it's full capabilities, it should have a metal area under or around it that will reflect the radio signal back onto the antenna..
    example: metal roof of vehicle .. or if on a building like a home, the antenna needs radials at the base of it to reflect the signal back onto the antenna itself. These type of antennas are called "Ground Planes"

    But the lack of a metal reflecting area does not mean the radio won't work.. it simply won't work as well as one with the metal reflector.

    To make things simple for you ... do this,

    borrow or buy a "Field Strength/SWR tester.. Commonly called an "SWR" meter. You will also need an 18 inch "jumper cable" to connect the meter between the antenna coax and the radio.

    Then based on the reading the meter shows, trim the metal antenna mast down, using 1/4" increments until the swr/reflecting wave is within proper tolerances.. usually less that "1" but can be as high as "2" without restricting your signals..

    If using a fiberglass antenna, the coax is the only way to correct the standing wave, without using a matchbox...

    Don't worry, the meter comes with instructions and diagrams on how to connect and use the meter..

    If for some reason you cannot get an acceptable match between antenna and radio by trimming the antenna or/and coax, there is a tuning device that you can get that will match the standing wave... In CBer's slang, the tuner is called a "Matchbox"..

    Make sure that the coax is not more than 20 feet long or less than 16 feet. The proper length of coax used on a 1/4 wave or 1/2 wave antenna is (+/-) 18' 6". Also do not coil up the excess coax.. stretch it out so that it does not overlap itself.. This can be done by stretching the coax out under or on the dashboard or up in the overhead storage area.

    NOTE: on some styles of antennas, the coax is shorter because of the way the antenna is made. The "Base Loaded" style of antenna is an example.

    I taped my excess coax to the inside wall of the overhead compartment over the windshield.. out of sight and worked great.

    Sometimes when people make up their own coax cables they accidentally allow the braided cable to ground out against the copper wire in the center of the coax or against the soldered connection of the PL259 connector.. (Thats the twist-on connector on the end of the coax)

    If you bought a ready made antenna with cable, it is not likely to have that problem.

    As for distance of a CB signal ... technically the signal emitted from a CB radio can travel completely around the world, but for practical purposes, the average distance that a CB is functional is about five or six miles on a open, flat terrain like some of those Texas or mid-western state's highways that seem to go on forever without a hill or mountain to be seen..

    I personally have talked to South America from my home in Raleigh, North Carolina.. with my CB by using a five element powered beam antenna on the rooftop of my home.

    That was 40 years ago during the CB craze that swept America. :) :) ahh for the good old days...

    Hope this helps,
    John KDX1663 The "Raleigh Mailman" (1967)
  5. Krazeehorse

    Krazeehorse New Member

    CB Antenna Ground

    Man, that was back when a license cost $20. You are OLD School John. Cool!
  6. TexasClodhopper

    TexasClodhopper Senior Member

    CB Antenna Ground

    KDU9847. That was my license number. The squeeks and squawks and wife drove me away from it. This was before all the loose profanity came into vogue.

    Did you know that CB frequencies were a mainstay in communications during WWII?

    Everything you said was pretty close to right, but even in doing all that you won't change much of the "get out" factor. You'll just be changing a meter reading. For practical purposes, your CB should be "deadened" so it is short range. Just down the road to the MHs in your group or your local park. Then you don't have to wear headphones! :blush:
  7. John Harrelson

    John Harrelson New Member

    CB Antenna Ground

    oops, telling my age again huh, Krazeehorse, rats! :)

    Thanks for bringing that point up about the matchbox not improving the signal a whole lot Texas, I should have noted that in my spiel ..

    With those old 23 channel tube radios like the Johnson White face and the Courier 25 channel, the match box would work wonders, but with the advent of the new 40 channel transistor radios, everything is pretty much set in concrete, and matchboxes are almost useless..

    I still have a couple of CBs, one in the truck and one in the 5th wheel, but they are seldom turned on.
    One reason is like Texas said, the disgusting language so many people use on the air and another reason is the cell phone of course.

    I still turn on the one in the truck if I think something might be causing a delay up ahead or if the weather is really bad in the mountain pass on US 50 when I travel to California for the VA hospital.

    A while back I had it on and was listening to a couple of truckers. I decided to give out with my old "Bucket Mouth" spiel that I used to use when I trucked for a living....

    "Kentucky Dixie Exray one six six three, this Carolina Cowboy is down and bound for those Carolina Towns ... with all eighteen going round and round... Going home, kiss a biscuit and eat mama, heh heh heh .. or eat a biscuit and kiss mama ... which ever comes first don't cha know ... we gone "

    "Carolina Cowboy" was the handle my friends gave me when I moved to the west coast..

    My old trucking buddies used to tease me about that as we chatted all night while we convoyed between Seattle and Great Falls on our regular bi-weekly runs..

    oh for the good old days... well, except for the day Mount St. Helens went off and grounded us all for ten days..

    have fun guys,
  8. Sober0782

    Sober0782 New Member

    CB Antenna Ground

    Thank you for all the Ideas, I will try them What I have is a Cobra 148 SS with a Wilson 3' stick and the antenna itself has a wire coming out of the bottom of the Stick for a ground. The match seems fine. Maybe I am just looking for two much as CBs are not like they were when I bought my first Citaphone LOL in the sixtys.
    I still have a president Washington SS base with a D104 Silver Eagle Mike. but not much chatter anymore except when the skip roles in. Thanks again Ed

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