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Why won't my am radio work with an old school antenna

Discussion in 'Trucking Electronics, Gadgets and Software Forum' started by Loaderlou, Oct 10, 2015.

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  1. Oct 10, 2015 #1
    Loaderlou

    Loaderlou Medium Load Member

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    Hi guys. I recently had my Pete roof repainted, new horns, new torpedo lights and went with an old school am fm antenna. When I tested the radio with the new antenna before installing it worked on am. Once I installed the antenna it only worked on fm. I bypassed the multiband antenna box as I did with my CB and installed the old school antenna directly to the radio. Any ideas why this would not work?
     
    Loaderlou, Oct 10, 2015
    Loaderlou, Oct 10, 2015
    #1
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  3. Oct 10, 2015 #2
    Skate-Board

    Skate-Board Road Train Member

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    That's strange. You can use a freaking clothes hanger and AM should work.
     
    Skate-Board, Oct 10, 2015
    Skate-Board, Oct 10, 2015
    #2
  4. Oct 10, 2015 #3
    Loaderlou

    Loaderlou Medium Load Member

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    I agree, can't understand it. It worked while I was holding it in my hand as a test. Once I drilled the hole and mounted it, dud. Can't be a ground cause I was holding it in my hand out the door. Never heard of grounding an antenna, you?
     
    Loaderlou, Oct 10, 2015
    Loaderlou, Oct 10, 2015
    #3
  5. Oct 10, 2015 #4
    baha

    baha Road Train Member

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    Try a clip to ground then to nut on back of ant. If ground on back of radio is poor am ant. will not work.
     
    baha, Oct 10, 2015
    baha, Oct 10, 2015
    #4
  7. Oct 10, 2015 #5
    Loaderlou

    Loaderlou Medium Load Member

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    It's an OEM Peterbilt antenna that I mounted on the roof. The roof is aluminum so that makes sense. But when I tested it before mounting, all I did was hold the antenna outside the cab after I plugged it in. Didn't touch anything to ground it. I'll give it a try tomorrow. Thanks Baha
     
    Loaderlou, Oct 10, 2015
    Loaderlou, Oct 10, 2015
    #5
  8. Oct 11, 2015 #6
    BoxCarKidd

    BoxCarKidd Road Train Member

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    I do not know but what changes between holding it in your hand and mounting it on the cab. Do you remember TV rabbit ears, aluminum foil, or yelling out the window to adjust the antenna? Sorry if you missed that. Some times they only seamed to work when when someones hand was on it. "Just stay right there and the rest of us can watch TV." The coaxle cable (Braided wire on the outside of the plastic tube with the antenna wire in the middle all covered in black outside) grounds to the cab when it is bolted down. Either that changed it or it shorted out on installation. Maybe, could be possible, or just hold it out the window, at least it is for your own enjoyment. Hopefully what baha said works.
     
    BoxCarKidd, Oct 11, 2015
    BoxCarKidd, Oct 11, 2015
    #6
    Skate-Board Thanks this.
  9. Oct 13, 2015 #7
    supersnackbar

    supersnackbar Road Train Member

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    I would say don't ground an am/fm antenna. My shop boom-box has an extra antenna that has a 5' wire hooked to it so you can move it around, but it's a loop and no way to ground it.
     
    supersnackbar, Oct 13, 2015
    supersnackbar, Oct 13, 2015
    #7
  10. Oct 29, 2015 #8
    beastr123

    beastr123 Road Train Member

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    the am antenna must be isolated from ground. If you did not get a rubber washer that isolates the exterior part of the antenna from the cab metal you can make one out of a old inner tube using a pair of scissors and cutting it at least a 1/8 " larger than the outside base. the inside mount does not have to be isolated as it is connected to the ground side of the coax cable.

    the quick test to check for isolation is to use a multimeter set on ohms or continuity and test between the inside and outside coax connectors at the radio end with it unplugged. then check the antenna itself to a ground. both checks should have NO continuity to ground!!!
     
    beastr123, Oct 29, 2015
    beastr123, Oct 29, 2015
    #8
    Skate-Board Thanks this.
  11. Oct 29, 2015 #9
    fargonaz

    fargonaz Road Train Member

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    AM antennas are usually internal to the radio, the frequency(<1MHz would be ~400' for a quarter wave) would make an external antenna very impractical. They are usually some thin wire wrapped around a ferrite bar.
     
    fargonaz, Oct 29, 2015
    fargonaz, Oct 29, 2015
    #9
  12. Oct 31, 2015 #10
    beastr123

    beastr123 Road Train Member

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    only the portable am radios have only an internal antenna.
    automotive radios require an external antenna.
     
    beastr123, Oct 31, 2015
    beastr123, Oct 31, 2015
    #10
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