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  1. #1
    doughboy's Avatar
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    Cobra 29 fatboy 24 pill dual 55 2 200 amp leece alts

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    55 antenna magic setup a two antenna bounce back system

    '55' Antenna Magic

    The basis for a good antenna system is a good ground, a good feed line, and
    sufficient ground plane.

    Two antenna systems do not require much planning, but if you are going to extend
    the system for shootout, then you need to map the system out before you start.
    The following text assumes previous antenna experience. The reflector antenna in
    all of the described systems will be grounded through a capacitor, although
    grounding the rear antenna will give close results.

    If you are planning on using only 2 antennas, a convenient spacing may be used
    between the two antennas anywhere from 6 foot to 86 inches. 6 foot will give the
    most gain for 2 straight sticks but cannot be expanded into a competitive 3,4 or
    5 antenna system. 86 inches will give the most gain for 2 coils and can be
    expanded into any shootout system.

    Regardless of spacing, in the 2 antenna system, you want some ground plane area
    in front of the 'HOT' antenna. Placement of the rear antenna farther back can
    also help in two ways, It closes the back door more since there is less ground
    behind the antenna: and it gives the 'HOT' more room in front of it.

    To quickly tune 2 antennas, place only one antenna in the 'HOT' position. Tune
    it for the lowest reflect. Next move this antenna to the rear. Put the second
    antenna in the 'HOT' position and start with it 5 inches shorter than the first
    one ended up at. Tune until the lowest reflect is reached. Very little fine
    tuning of the rear antenna may be necessary. If the antennas don't tune very
    quickly in this manner, then the antennas may not be resonant and other antennas
    should be tried.

    The performance of the two antenna system can be compared to a single antenna by
    changing from one system to the other. A station a few miles away can give the
    results for both receive and transmit. Another test with the two antennas is to
    transmit to the other station while turning your truck around. The station
    should report a large change in signal from the point at which you were facing
    the station, and the point at which you were facing away.

    Another test that you can perform alone, is to use a field strength meter and
    walk around the truck while your radio is keyed. Keep the same distance from the
    'HOT' antenna as you walk around the truck and you should get a good idea of the
    shape of your radiating pattern.

    Adding a third antenna requires bracket fabrication and usually is part of an
    expansion to four antennas. The bracket is usually made of 4 inch C-channel. It
    is grounded to the roof at the mounting point closes to the 'Hot' antenna, and
    is isolated by the insulators closest to the windshield. The insulators also
    serve as leveling adjustments. The antenna mount on the third bracket is
    isolated for RF. It should also be movable so the mount can be moved forward and
    backward on the bracket. The proper distance for the third antenna varies with
    the vehicle ground plane. Recommended values are from 40 to 50 inches.

    The length of the antenna will also vary with systems. It should not be longer
    than the 'Hot' antenna, and not shorter than 6 inches below the 'Hot' antenna.
    NOTE: when changing from a 3 antenna to a 4 antenna system, the third antenna
    will have to be adjusted both ways (height and distance), as you are adjusting
    number 4. The 3 antenna system does not show a large amount of gain on the field
    strength meter or on a receiving station several miles away. In competition, it
    provides the antenna system with more "Push Away" power when keying next to
    another truck.

    The four antenna system can be very different from one truck to another. The two
    basic types of brackets make the systems very different. One bracket system
    extends the bracket from the roof out to accept a fourth antenna about six foot
    from the number 3 antenna. The antenna mount is insulated and the antenna ends
    up pretty close to the same length as the third. The bracket is grounded at both
    ends. The other bracket system mounts on the front bumper and extends out a
    distance that changes with hood length and grill material type. Some grills are
    made of plastic and some are metal so the capacitance changes. If the bracket is
    metal, two choices of mounting are isolated and grounded. In the grounded
    system, the fourth antenna is very short, around 90 inches. In the Isolated
    mount, the antenna is much longer, 140 inches or more. If the bracket material
    is PVC, then you have an isolated system with a longer antenna, around 140
    inches or more. Both antenna systems work well but to decide which will work on
    your vehicle, you must spend some time tuning antennas and measuring gain. Keep
    notes on changes that you have made so you can find the best gain for your
    system and can revert back if things change to the bad. Good luck, and happy

  2. The Following 4 Users Say Thank You to doughboy For This Useful Post:

    ShadeTreeMechanic (01-29-2018), Silverado 996 (01-28-2014), the caveman (01-29-2014)

  3. #2
    Silverado 996's Avatar
    Silverado 996 is offline CB Junkies Donor Chat with me
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    •Ranger 2970N2•Cobra 29 LXLE•

    Join Date
    Aug 2012
    Round Rock, TX
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    Great write up!
    Silverado 996 back in the woods and I'm gone!
    * Cobra 29LXLE *
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    "It is not the strongest of the species that survives, nor the most intelligent, it is the one most adaptable to change, that survives"

    - Charles Darwin

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