Cal & Swr readings with Antenna warning light

Discussion in 'CB Radio Forum' started by zachary140, Jan 7, 2011.

  1. zachary140

    zachary140 Bobtail Member

    11
    1
    May 4, 2008
    Minnesota
    0
    In December I purchased a cb from Bells CB in Florida. I bought the Cobra 29 WX NW BT and had Bells CB peak and tune the cb as I figured for what I was going to spend it wouldn't hurt anything. I have read up a lot on the basics of antennas, grounding, and testing it to find out resistance in Ohms. I plow snow up in northern US so it is on a snow plow truck. My rig is a 1997 Ford 9000 tandem. I started out testing my coax cable which is approx 8 feet long. Both the ground portion of the cable together I got a reading between .3 to .4 Ohms and the hot pins I got .3 to .4 ohms. That is acceptable for that length of coax as I have researched. I also checked the mirror mount for Ohms to the ground on the battery. From the mount to the battery at the beginning I got a reading of 2.5 to 2.6 Ohms. I went out and bought 10 gauge braded wire and ran the ground wire to the frame which I tested to be more grounded than the mirror mount (Fiberglass door). I then attached the other side to the mirror mount so it came in contact with the mount itself behind a washer. This then dropped the Ohms down to 1.5 Ohms which I thought would be good. I then put in my new radio the Cobra 29 WX NW BT, hooked everything up and attached it to the dash. This radio has an antenna warning light on it so you don’t harm the radio while transmitting with a poor antenna or coax. I tuned the cb on channel 20 by the cal/swr knob until the needle lined up with the tip of the triangle and then went to see what the swr read and it was between 1.9 and 2.0. The antenna warning light comes on while on a dead key and from what the cobra manual said anything over 3.0 is unacceptable. Just because I can I took off my ground wire and tested the antenna and it read 2.0 - 2.1 ohms on the swr meter on the radio. I am not sure what antenna is on my truck as this is a new truck to me, but its approx 3 feet long black and the tip is missing off of it, and the plastic coating is cracked in a few spots. I just don’t know what to think with it at 2.0 and the antenna warning light is on. What should I look at and/or what should I do to get that down lower than 2.0 to make the antenna warning light to shut off? Did I over look something? Is the antenna bad? How can you test an antenna? I can hear people 2 miles away clear as a bell when it was snowing and blowing today with visibility at a half mile or less at times. I just listened as I just didn't want to burn up my radio. Thank you all for reading this and also for any help you may suggest. Once again any help with be greatly appreciated.

    - Zachary140
     
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  3. slowride67

    slowride67 Light Load Member

    142
    19
    Dec 26, 2010
    Southington,CT
    0
    I would start with the antenna sounds like that one is pretty beat up. I don't know if you're restricted to height but I use a Francis 4-1/2 foot on my work truck with a 18 foot coax.They are pre-tuned also so you don't have to worry about swr's. Just tip it forward or "bull dog" it as I do most driving on small roads with a tractor trailer. I run a galaxy 33 and can talk for thousands of miles when conditions permit. Never heard of anyone using 8 foot coax always told by radio techs they had to be in 3 foot increments 3-6-9- etc. I would try that first though just the antenna then get a new coax if problem not solved. Best of luck.
     
  4. zachary140

    zachary140 Bobtail Member

    11
    1
    May 4, 2008
    Minnesota
    0
    it maybe a nine foot coax i didnt measure we are not really restricted with height but the asphalt plants are very hard on antennas as they are lower clearance. i looked at another old truck and it has an antenna by the name of barjan or bargan i have never heard of the brand.
     
  5. slowride67

    slowride67 Light Load Member

    142
    19
    Dec 26, 2010
    Southington,CT
    0
    Barjan cheapest in truck stops not good quality. Would try a francis or wilson firestik. I just use francis out of ease just put them on and don't have to tune. Have a ground question. Did you run a single wire from antenna bracket to frame for ground? If so might want to try going from bracket to door hinge bolt then down to frame,single ground wires can sometimes act as another antenna so no matter what you do you'll never get swr's right. But would still try new bracket and antenna first could be one or other or both.
     
    zachary140 Thanks this.
  6. Hi. Try a short firestik or 9 foot s/s whip with a spring base.
     
    zachary140 Thanks this.
  7. zachary140

    zachary140 Bobtail Member

    11
    1
    May 4, 2008
    Minnesota
    0
    This morning I took off the other barjan antenna from the other truck and put it on mine. This one the coating was cracked a little bit on the bottom, but it still had a cap on the top. I tuned it out in the middle of no where and I still got an swr of 1.9 to 2.0 and the antenna warning light was still on. As far as my ground it is ran from my antenna mount near the stud. It is on the top side of the mounting bracket under the nylon washer and doesn't come in contact with the antenna stud. From there it goes in through the window that is never used into the dash and directly to the dash frame. I checked the Ohms on the frame and it was low at .02 to .04. I think I should ground to the door hing bolt and then to the frame to see if that makes a diffrence seeing as both antennas acted the same on the swr(granted they are cheap antennas) but they get beat up a easily. I think I will start with that, if that doesn't work I looked at the Wilson firestik FL3 with the tuneable cap on it. Is that a good choice to keep clearance low? I also would like to use the NOAA feature too so this seems like a good match in a 3 foot antenna. What is the diffrence from the FL3 to the FS3? Anything really big that I would be passing up on either of them? With buying either the fs3 or the fl3 I would have to buy a new mounting bracket and a stud if it didn't come with one correct?

    Thanks again,
    - Zachary140
     
  8. Rat

    Rat Road Train Member

    1.9 to 2.0 is not bad and will not harm your radio. You are not loosing all that much performance either.

    The warning light may have something to do with the P&T that the radio recieved. Especially if the limiter was clipped inside the radio. That is a no no.

    I would run down to the nearest radio shack and see if they have an SWR meter and some single coax and double check it with that also. The internal SWR meters on the cobra radio are sometime off. If you are getting less then 2.0 on channel 20 then I would go with it. You won't hurt anything with just a barefoot radio.
     
  9. longhaireddwb

    longhaireddwb Bobtail Member

    13
    2
    Jan 5, 2011
    0
    Not sure if you tried to tune your antenna. Sounds like your just taking a reading. You need an external SWR meter not the one in the radio. That one is just for reference. Check SWR on channel one. Then check it on channel 40. If on channel 40 the reading is higher than on channel 1 then your antenna needs to be shorter. Turn the screw in the tip on the antenna in a couple turns and take readings again. Or if your antenna don't have the tunable tip you will need to unwind some of the wire on the top of the antenna and cut some off. Put the cap back on and compare swr readings again. Your shooting for the same number on channel 1 and channel 40.

    At least a 4 ft tall antenna is needed. As far as the length of coax. That's a myth. What you need is the length that will go from your radio to your antenna. 18 ft or in 3ft increments is what people used to think. Its not the real deal. For a perfect VSWR reading you need coax at a special length depending on the velocity factor of the type of coax you use. This makes such a slight amount of difference that only when using an amp will this really mater!

    If you have tuned your antenna properly and 1:2.0 is the best you can get on channel 19 then you may need to correct the adjustment in the radio that allows the SWR light to come on. As what was stated before, a tune-up done improperly will make this light not work correctly. 1:2.0 is not that bad. I'd run it that way if that's the best I could get but don't go by the swr meter in the radio. Radio shack sells one for about 50 bucks and it reads properly.
     
    zachary140 Thanks this.
  10. zachary140

    zachary140 Bobtail Member

    11
    1
    May 4, 2008
    Minnesota
    0
    I have not had a chance to work on the truck since Saturday, but I did check on 1 and channel 40 and both are very similar in reading within .1 no more than .2 on the swr dead keys. I am going to try to ground to the hinge bolt first then jump it to the frame and see what that all does for me. I believe that the 2.0 is probably good, I will call and see what this guy did on my radio on Monday as well to see how he tunes a radio if the limiter was clipped and what not on his radios as I am not too sure at what I am looking at in the radio myself. I will post again when I find something out and when I get the ground switched up. Thank you all again.

    -Zachary140
     
  11. Rat

    Rat Road Train Member

    Open the radio and look at diode D11. If it is cut or missing then you will have found part of the problem.
     
    zachary140 Thanks this.
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