External swr meter has me confused

Discussion in 'CB Radio Forum' started by Don379, Oct 28, 2021.

  1. Don379

    Don379 Heavy Load Member

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    Setup Same for the past 4 years which is:
    Mirror mount wilson 2000 5" shaft and wilson gum drop mount.
    Mounted on mirror of peterbilt 379 at angle
    8' RG8X astatic coax
    Cobra 29 ltd chrome edition (yes the chrome edition is slightly different than the classic"
    Astatiic mic

    Radio has been acting up past couple weeks so i swapped in a new coax, new antenna and new mount.
    Astatic mic crapped out on me today so installed a roadking 56

    When i initally installed all my stuff years ago, i did so with my buddies good external swr meter and got my readings of 1.2 on channel 1 and 40. And to be honest, the cobra built in meter was pretty much dead on.

    Move ahead now, installed new components and tuned my new antenna last week with just the cobra swr. I have loud and clear 1.2 readings. I come in loud and clear for miles and transmit same way. I went ahead and bought a cheap 20 dollar astatic swr meter to verify, and the unit is telling me that my swr is in the red at 4. I figured maybe it was defective and forward at ref were reversed. but that wasnt the problem. I borrowed my buddies unit again. Low and behold readings of the same 4 swr.

    Whats going on here? The mic crapped out and also antenna light will blinking when transmitting. Grounds are great and cleaned the mirror grounds and have good ground plane. Also checked my ohms on the grounds. IS my cobra going out? Just doesnt make sense becuase its loud and clear but every so often i will get a bunch of static
     
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  3. Night Stalker10

    Night Stalker10 Road Train Member

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    Your biggest mistake is trusting the cobra 29 swr readings to adjust your new antenna. I had a fellow company driver complain about his new cobra 29LX not receiving or getting out very good. The Wilson antennas on his truck were rusty at the mounts and coax connectors. My antenna analyser showed a very high swr reading of 5 - 6 for swr. No surprise there. The cobra 29 swr meter showed a reading of 1.2. That seems to be the magic number for swr readings with these radios, no matter what the real swr is. The swr vr6 pot inside the cobra 29's are always out of adjustment from the factory.

    I would trust the cheap truck stop external swr meter any day before the cobra internal swr meter. I'm confused by what you mean by loud and clear 1.2 swr reading on your radio. You claim your getting out and receiving good, but that doesn't explain the high swr reading with the external meters. Did you install the coax connectors on the coax yourself? There's a problem in your antenna system somewhere. Never trim and tune an antenna by the radios swr meter. At least not the cobra 29s.
     
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  4. Ridgeline

    Ridgeline Road Train Member

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    What was it acting like?
     
  5. Don379

    Don379 Heavy Load Member

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    just a bunch of static even with squelch adjusted. put new antenna and coax on and fixed that issue
     
  6. Don379

    Don379 Heavy Load Member

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    i didn tcut the antenna. if anytging it would have needed to be extended which is easy to do. its adjustable. i can keep pulling it out and does nothing better
     
  7. Ridgeline

    Ridgeline Road Train Member

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    Well I would put the original antenna and mount back on with the new coax and see what happens.
     
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  8. Don379

    Don379 Heavy Load Member

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    ok. yeah somethin aint right
     
    Oxbow Thanks this.
  9. Don379

    Don379 Heavy Load Member

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    Well what good is a thread if you dont return back with the conclusion.
    I took night stlker and ridgeline advice.
    I hooked up a different antenna and was getting correct readings off the external swr. Was also getting same readings from cobra cb swr.
    Heres where it gets weird. I dont know if it has something to do with the wilson gumdrop mount or what. I only had to trim 1/4 inch off my last wilson,
    I actually had a spare whip in my shop. So i started by hacking 1/2 inch off whip. The external meter id not budge off of 4. So i said the hell with it and hacked 2 inches off. The swr now went below 3. All in all, i took off a whopping 3 inches or a little more. Thats a little redculous. Anyhow, i have 1.1 swr all across the board with the external meter now. Now the cobr internal meter is reading incorrectly at above 1.5.
    Hope i didnt fry my radio
     
    Timin770 Thanks this.
  10. craig_sez

    craig_sez Road Train Member

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    Try all your old gear then keep adding the new to see where the change occurs..
    Possible that its the piece of coax your useing with the cheap swr meter...
    Did you chk your grounds(bond points) with a multi meter,are you doin the old ground from bracket to chassie bs cause thats wayy wrong if ya are..
    As cars n truck get older rust and corrossion build to so keep that in mind..

    Replace all your bond straps(assumeing your not useing awg as gnd wire)
    Your gnd is not goin from ant bracket to chassie or battery right?
     
  11. Night Stalker10

    Night Stalker10 Road Train Member

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    It was a very busy weekend for me, so I haven't had time to check back. My main advise to your original post was to ignore the cobras built in swr meter and I gave you a reason why. You bought a new antenna, but you didn't say what brand and how long it is. Anything under 4ft long doesn't work the best for 11 meters. You bought new rg8x coax made by astatic. I've never used that brand of coax, hopefully the astatic coax is better than their new mics. What percentage of shielding does this coax offer? You want at least 95-97% shielding. According to the external swr meters (including your friends) you have an antenna system problem. Sounds like you resolved that by trimming down the antenna to get a good swr reading on the external swr meter. You say its weird that you had to cut off 3 inches to get a good swr reading compared to the original antenna. All antennas are going to be different. I like running the hustler 4ft antenna. Its a 10/11 meter antenna. I have to cut more off to use it on the 10 meter band than the 11 meter band. To me the real question is how much reflected power do you see. That's really more important than swr readings. But if your external meter doesn't have power reading capabilities, than you have to go by the swr readings. I would check the bonding like Craig suggested.
     
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