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Help! Antenna Behind Cab Mount and Ground

Discussion in 'Technical Chat' started by CowboyTaco, Mar 29, 2015.

  1. Mar 29, 2015 at 4:25 PM
    #1
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    I will start by saying that I've researched this and other forums up and down to the point that my head is starting to hurt. :p

    I'm not getting a good SWR reading, and I'm hoping that you can help.

    Some useful information:

    I have installed a Midland CB in my center console.

    Unit: https://midlandusa.com/product/1001lwxcb-radio/

    [​IMG]

    I have this 18' coax cable running from the center console up toward the engine, over the top of my feet, down the kick panel, through a grommet under the driver seat, along the frame and up between the cab and bed. There is absolutely zero slack in the line, and therefore no coils from excess cable.

    http://www.amazon.com/RG-58A-Coaxia...e=UTF8&qid=1427670045&sr=8-1&keywords=cb+coax

    My antenna is mounted on a mirror mount that I purchased from a Love's truck stop. I'm securing it to the bed rails using washers.

    [​IMG]

    I have a 10 ga. cable running from the antenna mount, down between the cab and bed and connected to some washers that i ground down to get a clean contact and pinched the cable. I also ground away the protective coating so that the washers would get good contact to the frame. I found no difference in SWR reading using 10 ga. or 8 ga. wire. I went back to the 10 as it was easier to maneuver down to the ground.

    [​IMG]

    I have a 3' fiberglass antenna that was compliments of another TW member. It's not in the best of condition, but the previous owner tested it before giving it to me and said that it worked just fine. Brand is unknown, but it is identical to the Truck Spec antennas that are sold at Love's. About half of it sticks above the cab.

    [​IMG]

    Tex was generous enough to loan me his SWR meter until I get it squared away. However, I've had it for quite some time and feel as though I need to return it. I've gotten my readings from way in the red to right on the line of where the red starts by adding the ground cable. This is right at the 3 on the top line. This picture is not of the actual one I'm using, but figured I'd put this out there just for illustration purposes.

    [​IMG]


    Now that the useful info is out of the way, please do not tell me that my antenna is mounted in a terrible location. I know that this location is not ideal for several reasons. However, I do know that other people have successfully mounted similar antennas in the same location and that it will work. I'm not planning to communicate with people 50 miles away. I will be happy with less than 2 miles.

    If your only advice is to move the antenna to the top of the roof, rear of the bed, or hood of the truck, please do not reply as I'm trying to avoid those options (though I know they are better).

    Thank you in advance for your help with this. I feel like I'm at my wits end here. TW has been an incredible resource for this and many other projects (though it has emptied my wallet a few times :rolleyes:). Any advice on how to get a better reading is appreciated.

    So, with all that being said, how can I make improvements?

    I'll be happy to take any additional pictures if you think they would be helpful.
     
  2. Mar 30, 2015 at 6:14 AM
    #2
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    Monday morning bump.
     
  3. Mar 30, 2015 at 7:22 AM
    #3
    nzbrock

    nzbrock Well-Known Member

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    Hard to tell from the pictures, but is the mounting bolt(s) contacting the coax end? Can this affect anything? I cannot remember if the end screw sleeve is the ground, but if it is not, you need to correct this.

    Obviously you know mounting the antenna to the plastic bed is not ideal. Is it possible to add a piece of flat steel or angle to extend the grounding plane? Maybe instead of bolts in the rail, try finding a long piece of flat steel that you can drill and tap holes in to use as your mounting nuts. This could extend feet down the rail and could improve reception. I am not sure if this would work, just a suggestion.
     
  4. Mar 31, 2015 at 5:31 AM
    #4
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    The mounting bolt is not touching the coax end. The coax is centered between the two bolts. I have thought about trying to make a more solid backing to go in the channel, as well as some sort of shim to straighten the antenna. It is straight now, but I have to hold it in place and tighten down the bolts.

    I see a lot of stuff about the plastic washer. You can see in the pic that I have it on the top, but I've seen some kits that have two. One on top and one on bottom. Would this effect anything?

    Do I have a good ground? Should I try to make contact with anything else?

    Should I try a different antenna? I'm not really interested in a whip, but I'd get one if it meant that it would work. They have a 4 foot whip at Loves for under $20 through the end of April. I'd prefer to get a 2' fiberglass antenna to keep on 90% of the time, as I could keep that in and not worry about hitting the garage door.

    I've also heard some people say to make sure you have a good ground to the radio. Right now, I have the ground cable that came with the unit spliced to another wire and running it to under the dash on the passenger side.

    Spliced with one of these:
    [​IMG]
     
  5. Mar 31, 2015 at 5:56 AM
    #5
    nzbrock

    nzbrock Well-Known Member

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    I don't think it would hurt to try out the walmart antenna and see if there is any improvement. You can always return it.

    From experience on my truck, the frame at the rear is rather poorly grounded. I discovered this when I installed LED reverse lights. LEDs need much more precise power than incandescent and were not working when simply grounded to the frame.
     
  6. Mar 31, 2015 at 6:43 AM
    #6
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    So what did you do to improve the ground?
     
  7. Mar 31, 2015 at 9:06 AM
    #7
    nzbrock

    nzbrock Well-Known Member

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    For the lights I ended up running a wire back to the source (battery).

    I used to have a cb antenna mounted on a custom mount at the rear of the bed (first gen). It was anchored to the sheet metal by the tailgate latch and I never had too many issues with it.

    If you haven't already, go through these steps: http://www.wearecb.com/testing-cb-antenna-ground.html
     
  8. Mar 31, 2015 at 11:21 AM
    #8
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    I've opened the link and will be going through there shortly.

    Interesting...

    Where were you grounded?

    How far over behind the cab?

    Any pics?

    I'll be trying this later tonight.
     
  9. Mar 31, 2015 at 6:36 PM
    #9
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    Well, I was hopeful, but no such luck. I tried moving it to the rail directly behind the cab and now getting worse SWR. It went from 3 to approx. 3.5. I thought maybe moving it behind the cab would somehow use the roof as more of a ground plane (if I understand that concept correctly), but i guess that is not the case?

    What do you mean by the ground is direct on the antenna? Any chance you have a pic from the underside of the mount showing contact with the antenna? I'd also be interested in a pic of the grounding point if that isn't too much to ask.
     
  10. Mar 31, 2015 at 9:24 PM
    #10
    Sandman614

    Sandman614 LRGRNR

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    I'm sure you've seen this in your research but it can't hurt to double check, also points out connectivity and plastic washer location. Grab a multi-meter and check this. Sounds like your setup is similar to the first diagram on left.
    [​IMG]
     
  11. Apr 1, 2015 at 4:23 AM
    #11
    LUSETACO

    LUSETACO Here for the Taco Pron

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    I would look into your mount. It doesn't look like much of it is making contact with the rail. Running a wire for a ground typically does not do much. I could never get an antenna to work on the bed rails myself. I would revise that mount or try a longer antenna.
     
  12. Apr 1, 2015 at 4:31 AM
    #12
    MJS

    MJS Well-Known Member

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    I'm getting SWR around 1.3 at channel 20 with mine just barely peaking over the cab.

    Wilson 24" silverload, drain wire disconnected (was hurting SWR), grounded directly to the frame above the rear driver bump. Also added a ferrite at the CB end because there was some signal traveling down the coax shield.

    Also I grounded the three bed rails together to extend the ground plane with 10awg wire.
     
  13. Apr 1, 2015 at 4:49 AM
    #13
    mjackson92rs

    mjackson92rs Well-Known Member

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    A couple of things to check:

    1. Move the antenna around a little bit (closer to the cab) in small incriments, maybe an inch at a time, and check SWR at each spot.

    2. Your ground wire looks ok, except for pinching the wire between the bolt/washer. You should really use the proper ring terminal here, but I'm sure you're fine for now.

    3. Get a multimeter and check continuity from the antenna mount to a chassis ground, to ensure your ground wire is working. Check continuity from the (+) of the coax to the (-) of the coax, you shouldn't have it between the two.

    4. If your continuity checks out ok on the coax, start tuning the antenna. Some of the fiberglass ones have an adjustable tip to dial in the SWR. Others require trimming the excess length from under the rubber cap. If you need help with this, let me know and I can link to you some good articles.

    You should be able to get that SWR down to at least 2:1, which I would consider acceptable for the location.
     
  14. Apr 1, 2015 at 4:50 AM
    #14
    mjackson92rs

    mjackson92rs Well-Known Member

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    Also, try the bolded statement above. Would only help you and should be pretty easy to do.



    I've had good results with my VHF/UHF dual band in this location:

    [​IMG]
     
    Last edited: Apr 1, 2015
  15. Apr 7, 2015 at 11:04 AM
    #15
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    Sorry to keep everyone waiting. We went camping for the Easter weekend, so I have not been at a computer.

    I was not checking it, mainly because I didn't know what to check for. However, I did watch the video posted above. I have this cheap (free) Harbor Freight multimeter, but I'm afraid I don't know a whole lot about what each setting measures.

    http://www.harborfreight.com/7-function-multimeter-98025.html

    On one of the settings (can't remember which, but I'll look tonight when I get home) I got a reading of 1.8 when I touched the two ends together. I also got 1.8 when I touched one to the antenna mount and the other end to the point where the ground meets the frame. Because of this, I thought "Great, the ground is good." But when I touched the black cable to the other side of the ground, the number jumped from 1.8 to something in the 73 range. I'm not sure what or how that could happen.

    Yes. Similar to the diagram on the left. Exactly that.

    I'm not sure how I could get more of it to contact the rail. :confused:

    I'll look into doing this as well. Any more info (or possibly pics) of where you grounded each rail?


    Answers to the above questions:
    1. I tried that. Each location seems to be about halfway through the red of the SWR meter, which is worse than I originally had.
    2. I will likely put a proper connector there once all is said and done. I don't have many left and wanted to make sure that this location and wire were going to meet my needs first.
    3. I'll try to check that out tonight.
    4. Will do. The antenna actually looks fairly abused, but i figured since it checked out with the previous member that it should be tuned. I'm considering purchasing a new one. I know longer is better, but a 2' antenna could stay in 100% of the time.
     
  16. Apr 7, 2015 at 11:23 AM
    #16
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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  17. Apr 7, 2015 at 11:53 AM
    #17
    LUSETACO

    LUSETACO Here for the Taco Pron

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    Are you tuning the screw tip or just moving it around? Just because it was tuned by the previous owner makes no difference. Also when you are checking your SWR make sure you're in a wide open area away from buildings and power lines, I don't think a shorter antenna will help.
     
  18. Apr 7, 2015 at 12:47 PM
    #18
    CowboyTaco

    CowboyTaco [OP] Well-Known Member

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    I have tried in my neighborhood as well as in an open field with little to no difference in readings.

    The antenna that I have does not have the adjustable tip. Only way for me to tune it is by trimming, and I'm afraid I may trim to much if that isn't the problem.
     
  19. Apr 7, 2015 at 12:47 PM
    #19
    jmaack

    jmaack Well-Known Member

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    Are you sure the cable is in fact good?
     
  20. Apr 7, 2015 at 1:08 PM
    #20
    LUSETACO

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    May be time for a new antenna then. I personally wouldn't do the 2 footer. I know you want convenience but they generally don't have much for range, especially if it's right behind the cab. The 2 footer mounted off the rear of the bed may be so so for performance. Will you be using the CB all the time or just for wheeling? You could go for a 4 foot with a fold down mount.
     
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