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Watt the Hell......

Discussion in 'General CB Services Discussion' started by Cruiseomatic, Dec 1, 2013.

  1. Cruiseomatic

    Cruiseomatic Dark side of the Sun.

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    Keyed a Cobra 200 up in the truck, Instrument panel went ape shit. All lights but 2 came on, Fuel gauge went empty, and while driving, Speedometer kicks it own ass back to 0 very fast. Repeatedly. After the 3rd time the security light came on and stayed on. This truck doesn't have a factory alarm. According to my RS SWR meter I have a 1:1 match at PEP on 27.185. No Ant. indicators kick on. Coax is not coiled, pinched, sharply turned, etc... On my buddies mfj-259 it shows anywhere from 4.8 to 10 db coax loss at different freqs. It also shows high as SWRs where all my other test equipment shows low.



    Specs:
    '01 Silverado Base LT
    3' Firestik II
    K40 50-ohm coax (Not sure type, Pulling dash apart in the morning to look.)

    I'm thinking I need to bond the body together with straps since the chassis isn't doing it.
     

  2. M0GVZ

    M0GVZ Sr. Member

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    Common mode. How have you mounted the antenna?

    Low SWR means nothing really other than a 50 Ohm match is being presented at the PL259. It doesn't tell you how good your RF ground is or if you have common mode current present on the outer of the coax braid.
     
  3. Cruiseomatic

    Cruiseomatic Dark side of the Sun.

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    Common mirror mount onto truck backrack with solid contact between mount and rack. Rack has body ground and 10 ga. ground wire to chassis. I do have a coax ferrite core I could try.
     
  4. Cruiseomatic

    Cruiseomatic Dark side of the Sun.

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    .........
     
    #4 Cruiseomatic, Dec 1, 2013
    Last edited: Dec 1, 2013
  5. Lil'Yeshua

    Lil'Yeshua .......

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    RF in the shack,er, mobile?
     
  6. W5LZ

    W5LZ Crotchety Old Bastard

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    I can't tell you how, but it's evident that RF is getting into the truck's computer. That computer can cause all the things you described when it's a bit 'crazy' with RF. The solution is to keep the RF out of the computer. And hopefully it will 'recover'.
    Why is RF getting in? Beats me, something is too close to it or maybe the computer's wiring harness isn't as 'shielded' as it should be (the things aren't shielded at all to my knowledge). Having run HF in a Silverado before I can say that what's happening with yours is not that common at all. It's certainly possible to do some 'filtering' of that wiring harness, torroids etc, but it isn't easy! That harness is all over the truck, not just at the computer's end, you know? Bonding body panels together is one thing to try, but don't count on that 'curing' it. Rerouting all the radio's wiring would also be beneficial, keep it away from ANY wiring in the truck as much as possible. SWR has very little to do with it, but those CMCs probably do. You can have CMC with a well tuned system, it doesn't care what the SWR is.
    Good luck.
    - 'Doc
     
  7. Lil'Yeshua

    Lil'Yeshua .......

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    Check that coax. You might need coax with better shielding. My K40 magmount coax would pick up my iPhone noise in my car. I changed to a Sirio Magmount along with a Performer PL5000. Now my radio only picks up my iPhone noise when I stick the phone out the window near the roofline. Just something to consider.
     
  8. Z-MAN 369

    Z-MAN 369 Active Member

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    Get better (thicker) coax, then maybe have your 200gtl tuned. Remember the 200's & 150's were Cobras attempt (failed) to make a 10 meter radio. Could be a splatter box.
     
  9. space cowboy

    space cowboy Quack Quack

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    could be the antenna is just too close to the computer, try the other mirror.
    shielded coax is also an option, these days it can be hard to avoid running coax next to the vehicle wiring.
     
  10. Ratfink

    Ratfink Active Member

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    Good coax, good ground and proper bonding will cure most problems. No cut corners when doing an install it will come back and bite you.
     
  11. The Jerk

    The Jerk Active Member

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    Nothing will cure a splatter box radio...

    Sent from my SAMSUNG-SM-G730A using Tapatalk
     
  12. AudioShockwav

    AudioShockwav Extraterrestrial Admin
    Staff Member

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    True Dat.
    Headache racks can present additional problems that extra grounding may help.
    I would doubt the 10 gauge is helping much with this, you need a much wider strap or some 0 gauge welding cable with good solid copper terminals attached to it.
    Clean the spot on the truck were you plan to hook it at the frame.
    Clean as in remove any paint/undercoating to bare metal, bolt it securely and then apply some spray undercoat or some good paint, same thing at the rack.
    Sure the 10 gauge will show ground to DC, but RF is AC and likes a nice low resistance low inductance "fat" ground to look at.

    This is why a puck on the top is the best.


    73
    Jeff
     
    #12 AudioShockwav, Dec 1, 2013
    Last edited: Dec 2, 2013
  13. Watergate

    Watergate Well-Known Member

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    Just a note on your security light. It may not have a factory alarm, but an '01 does have a chipped key. Get a $1 Wal-Mart key made for the truck and try to start it. That light will pitch a fit.
     
  14. Cruiseomatic

    Cruiseomatic Dark side of the Sun.

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    Wow, Lot to reply to. Coax is RG8X 95% sheild and stiff as a damn 2X4 when cold. It is running away from the vehicle harness. The rack has a body ground with the 10 ga. from mount to rack just in case. There is solid contact between mount and rack. Antenna is as far away as I can practically get it. I did put a ferrite core over the coax about 16" away from the antenna and it wasn't as bad. Truck does not have a chipped key. It has an aftermarket ignition switch and remote starter. Matter of fact, One night ign. switch stuck on start. Removed key and tumblers, re-installed switch and for 6 months drove with no key. Antenna is also mounted above roofline.
     
  15. The Jerk

    The Jerk Active Member

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    I still think you have a radio tuning issue, and no amount of shielding, bonding, or coax will help if the output from the radio itself is splattered.

    Im running a 100 watt General HP40w in a 2012 Silverado with zero issues. But the radio was tuned correctly.

    Sent from my SAMSUNG-SM-G730A using Tapatalk
     

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