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Ground Plane and antenna mount

Discussion in 'Communication (CB | GPS | HAM)' started by Chris_T, Aug 12, 2003.

  1. Chris_T

    Chris_T 1/2 ton status

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    I have a '72 K5 and normally run topless. I was looking to mount a CB antenna to the swing out tire carrier which would put it about 6" above the tailgate. Mostly for trail rides and such, though I'm sure I'll find more and more uses for it once its in there.

    My Q is - will sticking it up that high have an adverse effect compared to, say, a mag mount in the middle of the hood?
     
  2. rebelk5frk

    rebelk5frk 1/2 ton status

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    About the only thing you might notice with it on the tire rack is the antenna will be a bit more directional. You will have stronger signals towards the front. It would be similar with the antenna on the hood but would be slightly stronger towards the rear instead.

    I'd say mount it on the tire carrier so it is out of your line of sight while driving. The difference in signal strength from the front to the rear won't be very noticable unless you are trying to reach long distances.

    Just make sure the antenna has a good RF ground to the body. A lot of the time with swinging tire mounts there isn't much contact between the arm and the body of the vehicle due to the bearings and/or bushings. A thick guage wire mounted to the arm and body will work ok but a copper strap or even a braided ribbon would be better.
     
  3. Chris_T

    Chris_T 1/2 ton status

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    Better to the front because the bed creates the ground plane?

    Secondly, do I want to ground it to the body or to the frame? Make a difference?
     
  4. rebelk5frk

    rebelk5frk 1/2 ton status

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    The ground location doesn't matter much. It's easier to just ground to the nearest sheetmetal.

    The signal will be stronger to the front with it mounted in the rear because the groundplane is the "second half" of the antenna. A perfect groundplane would be a large circle (about 18ft diameter) but we don't drive big circles so the radiation is focused in the direction of the most metal.

    hope that made sense.
     
  5. Chris_T

    Chris_T 1/2 ton status

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    Perfect sense .. but since you're willing to answer questions ....

    How far from the base of an antenna does the ground plane have to be to be effective? in theory I could mount it to the roll bar if I never wanted to put the soft top up, but then the plane would be hood level in the front and bed level in the rear. I'll probably go with the rear tire mount, but I'm curious about the antenna functions.
     
  6. rebelk5frk

    rebelk5frk 1/2 ton status

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    Well since the rollbar is metal and is connected to the rest of the metal body, the groundplane would "start" at the rollbar. Generally the higher and closer to center of the vehicle the better.

    A lot of guys I know that have regular trucks mount a bar on the tool box or in the bed behind the cab that reaches just above the cab. Then they mount the antenna to the top of the pedestal so the whole antenna is above the cab and not being blocked by anything. The use of the extra pedestal keeps from drilling holes in the cab, gives a more sturdy mount, and normally puts the antenna closer to the center.
     
  7. behemoth

    behemoth 1/2 ton status

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    Hijack time !!! /forums/images/graemlins/laugh.gif

    [ QUOTE ]
    ... Then they mount the antenna to the top of the pedestal so the whole antenna is above the cab and not being blocked by anything...

    [/ QUOTE ]
    So that would explain why my handheld CB doesn't work real well inside the truck, right? I have to open the sunroof and stick the dang antenna up through the roof to get any distance on it!! /forums/images/graemlins/shocked.gif
     
  8. rebelk5frk

    rebelk5frk 1/2 ton status

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    [ QUOTE ]
    So that would explain why my handheld CB doesn't work real well inside the truck, right? I have to open the sunroof and stick the dang antenna up through the roof to get any distance on it!!

    [/ QUOTE ]

    Basically yeah. Also with the antenna inside the vehicle it is mostly surrounded by metal and is blocking your signal. Holding it just above the roof of the cab does two things. It get's it out in the open and to a point also uses the vehicle body as a ground plane. /forums/images/graemlins/thumb.gif
     
  9. Z3PR

    Z3PR Banned

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    [ QUOTE ]
    [ QUOTE ]
    So that would explain why my handheld CB doesn't work real well inside the truck, right? I have to open the sunroof and stick the dang antenna up through the roof to get any distance on it!!

    [/ QUOTE ]

    Basically yeah. Also with the antenna inside the vehicle it is mostly surrounded by metal and is blocking your signal. Holding it just above the roof of the cab does two things. It get's it out in the open and to a point also uses the vehicle body as a ground plane. /forums/images/graemlins/thumb.gif

    [/ QUOTE ] That and the fact that handheld CB's suck to begin with. I've never seen a handheld get more the a mile in the real world anyways. /forums/images/graemlins/ignore.gif
     
  10. rebelk5frk

    rebelk5frk 1/2 ton status

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    [ QUOTE ]
    That and the fact that handheld CB's suck to begin with. I've never seen a handheld get more the a mile in the real world anyways.

    [/ QUOTE ]

    Nah...if you have one that puts out full power and hook it to a good antenna they'll talk just fine. I've used them from time to time and could talk 8-10 miles on a quiet day.
     
  11. 88Silverado

    88Silverado 1/2 ton status

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    You can get around the groundplane on your walkie-talkie by using an end-fed Half-wave antenna...but for 11 Meters it would be around 18 feet. /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  12. Z3PR

    Z3PR Banned

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    [ QUOTE ]
    [ QUOTE ]
    That and the fact that handheld CB's suck to begin with. I've never seen a handheld get more the a mile in the real world anyways.

    [/ QUOTE ]

    Nah...if you have one that puts out full power and hook it to a good antenna they'll talk just fine. I've used them from time to time and could talk 8-10 miles on a quiet day.

    [/ QUOTE ] There's that big IF thing. A good antenna will make a world of difference, but, if we're talking just a handheld unit using the antenna that comes with it, that's a completely different story. /forums/images/graemlins/deal.gif
     
  13. 88Silverado

    88Silverado 1/2 ton status

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    [ QUOTE ]
    using the antenna that comes with it, that's a completely different story

    [/ QUOTE ]
    That is true. The short-loaded antennas are fairly close to a dummy load. Remember, nothing is free. you give up performance for convience of length, same with a 102 whip vs a firestick. I use a 2 meter handheld with a 5/8 wave external antenna on my Blazer, works much better than the 4" rubberduck antenna it came with /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  14. Z3PR

    Z3PR Banned

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    [ QUOTE ]
    [ QUOTE ]
    using the antenna that comes with it, that's a completely different story

    [/ QUOTE ]
    That is true. The short-loaded antennas are fairly close to a dummy load. Remember, nothing is free. you give up performance for convience of length, same with a 102 whip vs a firestick. I use a 2 meter handheld with a 5/8 wave external antenna on my Blazer, works much better than the 4" rubberduck antenna it came with /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif

    [/ QUOTE ] On my K5 it's a 102" stainless Steel whip, or no radio equipment at all. In my personal opinion, for a CB, nothing beats a 102 !!!! /forums/images/graemlins/thumb.gif Think my next radio for the K5 will be a 93T I'll add a "Doorbell" that dings when I key the mic, and a "K" beep. Both with have on/off switchs.
     
  15. behemoth

    behemoth 1/2 ton status

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    [ QUOTE ]
    I've never seen a handheld get more the a mile in the real world anyways.

    [/ QUOTE ]
    Must not have seen to many then - My Radio Shack 40 ch. TRC-226 gets out real well except IN the truck. I've had it for years. It was $150 new - paid $100 for it on sale about 10 years ago. /forums/images/graemlins/laugh.gif
     

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