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How many feet of coax for dual?

Discussion in 'CB Radio Forum' started by The Twilight Zone, Dec 16, 2011.

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  1. Dec 16, 2011 #1
    The Twilight Zone

    The Twilight Zone Bobtail Member

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    Sep 7, 2011
    Cobb Island,Maryland
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    I have read many many posts and i am trying to figure how many feet of coax i need for a dual set-up in a Cascadia....I changed the mounts on the side of the cab with aftermarket ones so i now can use any antenna...I am gonna be running a ground wire from each mount to a solid ground....I am gonna replace the junk coax that freightliner uses but i am wondering how many feet in total do i need?..I have seen some coax already set up for duals in some truck stops and it says it is a total of 18 feet....is that good enough?....i am also gonna install a real swr meter.....am i missing anything else? thanks
     
    The Twilight Zone, Dec 16, 2011
    The Twilight Zone, Dec 16, 2011
    #1
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  3. Dec 16, 2011 #2
    Thpbltblt

    Thpbltblt Light Load Member

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    May 18, 2011
    Dacula, Georgia
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    Don't know about length, but I can tell you that I remember reading that you need to use a different resistance coax for a dual set up than you would for a single. Not sure what it is off hand, though. Someone else will chime in to help you out, I'm sure.
     
    Thpbltblt, Dec 16, 2011
    Thpbltblt, Dec 16, 2011
    #2
  4. Dec 16, 2011 #3
    Rat

    Rat Road Train Member

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    Rats nest Grafton North Dakota
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    Cophased (dual) coax is 75 ohm were single phased coax is 50 ohm.
     
    Rat, Dec 16, 2011
    Rat, Dec 16, 2011
    #3
  5. Dec 16, 2011 #4
    AB7IF

    AB7IF Light Load Member

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    Jun 11, 2011
    Somewhere, Ar
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    What Rat said plus each side an odd multiple of quarter waves long given the frequency and velocity factor. Meaning for RG59 on channel 20; 6 feet, or 18 feet, and so on. Typically each leg is 18 feet of 75 ohm coax for a CB dual coax hanging on the rack in various truck stops. There are bad ones out there made from 50 ohm hanging in truck stops so be sure before you buy. Barjan or Truck Spec 300-528 or Firestick Fireflex is going to be correct.
     
    AB7IF, Dec 16, 2011
    AB7IF, Dec 16, 2011
    #4
  7. Dec 16, 2011 #5
    The Twilight Zone

    The Twilight Zone Bobtail Member

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    Sep 7, 2011
    Cobb Island,Maryland
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    thanks for the info.....gonna get some tomorrow and install it during my 34 reset.
     
    The Twilight Zone, Dec 16, 2011
    The Twilight Zone, Dec 16, 2011
    #5
  8. Dec 17, 2011 #6
    The Twilight Zone

    The Twilight Zone Bobtail Member

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    Sep 7, 2011
    Cobb Island,Maryland
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    thanks again guys...spent all day running the cable and a ground wire behind all the overhead dash and cabinets.....wasn't too bad as i used to work on trucks years ago.....boy freighliners cb coax is cheap as anything.....cut the old coax....did leave it tucked down.....radio still works just as good as before......and it seems like the cb works better....real test will be on the road and not in a truckstop...well after my reset i will know...thanks again guys it really helped.
     
    The Twilight Zone, Dec 17, 2011
    The Twilight Zone, Dec 17, 2011
    #6
  9. Dec 18, 2011 #7
    this_is_nascar

    this_is_nascar Light Load Member

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    Jun 25, 2008
    Gloucester City, NJ
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    Don't know the answer to the coax question, but I will tell you if you can't get those duals at least 9' apart of each other, than it's going to be a waste of time and effort and you should run a single antenna.
     
    this_is_nascar, Dec 18, 2011
    this_is_nascar, Dec 18, 2011
    #7
  10. Dec 18, 2011 #8
    Xcis

    Xcis Medium Load Member

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    Jul 9, 2008
    Bridgeport, Pa
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    I don't know if this will reach you in time but I hope this may help anyone else that is reading this thread.
    .
    If the coax installed in the truck gives you a low enough SWR reading, I would just use it. Changing coax will not give you much in the way of performance boost for the money spent.
    .
    However, if the coax is damaged that is a completely different issue. I would bypass the dual antenna setup and go with a single antenna setup.
    I would put one antenna on the driver's door and run RG 58 or RG8 to the radio. I ran cable once on a job and swore I would never do that again.
    .
    When you wrote about grounding, you got me a little confused. If you are referring to connecting the large metal components of the truck into a large antenna ground plane, that is called "bonding" and the connections from part to part should be kept as short as possible. Do not run a wire from the antenna mount to chassis ground. If applicable, a search for "antenna ground plane" should provide you with much needed detailed information.
     
    Xcis, Dec 18, 2011
    Xcis, Dec 18, 2011
    #8
  11. Dec 18, 2011 #9
    WA4GCH

    WA4GCH Road Train Member

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    Seminole Florida
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    :biggrin_25513: RG-8 WHY? 58 should take at least 500 watts
     
    WA4GCH, Dec 18, 2011
    WA4GCH, Dec 18, 2011
    #9
  12. Dec 19, 2011 #10
    The Twilight Zone

    The Twilight Zone Bobtail Member

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    Sep 7, 2011
    Cobb Island,Maryland
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    I did not not have a full proper ground at the antenna's......(I used to work on trucks and cars)...checked with an ohm meter and the ground was real lousy....so i ran a short wire to a common ground and now it is properly grounded....you would be really surprised how a lot of things in vehicles do not have the proper ground they need(this is partly where electrical problems happen. got everything done and i will have to say that it seems to be doing reaqlly good...my swr's couldn't be any better and i can get out farther than the parking lot..lol...next is to upgrade the mike.
     
    The Twilight Zone, Dec 19, 2011
    The Twilight Zone, Dec 19, 2011
    #10
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