antenna light coming on cobra 29

Discussion in 'CB Radio Forum' started by panhandlepat, Dec 27, 2007.

  1. panhandlepat

    panhandlepat Road Train Member

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    i got switched to a newer truck last month, great right? WRONG LOL. the terminated driver CUT the coax off and i have no idea where the original power wires went. i got power to the radio, and ran an 18' coax (recommended length for my Francis antenna) now a month later i just noticed my "antenna light" coming on. i am not sure how long it has been because i usually don't look up at the radio when i key up to talk LOL. my SWR is about 1.5 and all coax and power connections are tight. any idea what might be wrong???
     
  2. Carolina Thunder

    Carolina Thunder Medium Load Member

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    Are you reading the SWR from the radio? If so then NEVER go by the factory swr meter on any radio! They read close but are in no way completely accurate. You should have a shop set it or go out and buy a cheap SWR meter from radio shack and do it yourself, save money that way. You could just be losing ground and that will cause your SWR to rise. Clean off the spot were you have it mounted and then try it.

    Tell me this. What kind of antenna, what type of truck and where is it mounted?
     
  3. panhandlepat

    panhandlepat Road Train Member

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    int. 9400I, it is a 4.5 ft francis mounted to mirror bracket (welded on) i even swapped ant. to a KW factory 4 ft that was left on truck with same result
     
  4. Carolina Thunder

    Carolina Thunder Medium Load Member

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    Try new a antenna stud and make sure the little plastic washer is on top between the antenna and bracket...not on the bottom between the antenna stud and bracket. You may have to find a antenna with an adjustable tip on it. That way you can tune the antenna to the truck and you should see a decrease in you standing wave. The antenna you have now can not really be adjusted although some do clip off a little length from the antenna at a time to get the swr down but if you clip to much then you will have to buy another antenna. Anyway...try a new stud first and let us know how it works out.

    Here is something you may not know that i want to touch on for a moment.
    You do not want the coax coiled up. You want to lay it out about 2 foot in length and then fold it over onto its self back and forth until you can tuck it away. If you coil coax into a tight little ball it will create what is called an RF choke. Basally what that does is the more you talk the higher the SWR will go because it builds up energy that will not pass to the antenna because of the choke effect. Where as if the coax is just folded the power passes thru the coax with less effort and your SWR will be lower.

    I know, kinda sounds weird but with out getting to technical this is the reason you dont want to coil coax up.
     
  5. panhandlepat

    panhandlepat Road Train Member

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    well crap, i thought i had read to loosely make a large (about 10 in is what i have) coil and have it either close to the radio or close to the antenna. i will investigate further when i get back in my truck tomorrow. thx for the info
     
  6. Pur48Ted

    Pur48Ted Road Train Member

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    Actually, there is no need to have 18feet of co-phase. All you need is enough coax to go from the radio to the antenna(s)
     
  7. panhandlepat

    panhandlepat Road Train Member

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    why would the antenna package suggest 18 ft. for "best results"
     
  8. RNGTransport

    RNGTransport Light Load Member

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    Francis ant actually need an 18' coax since they are pre tuned to work that way. I would check the grounds again. And try putting a new stud thru the welded bracket. I would suggest a wilson stud.
     
  9. panhandlepat

    panhandlepat Road Train Member

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    10 on that. i figured, with my limited knowledge ,it had something to do with the coaz actually being part of the "antenna" thx
     
  10. Pur48Ted

    Pur48Ted Road Train Member

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    Ask any "Certified" radio repair tech (not the guy that installs noise-boxes) and he will tell you the same. I have used as short as 4ft co-phase and had better SWR than the Truck-Stop stock packaged coax.
     
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