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  1. #11
    Bobtail Member
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    Alright this is what I have got. Diode D11 is still there untouched. I bought the SWR meter from radio shack with a short jumper with factory ends. SWR on channel 1 - approx 3.5 Channel 20 - approx 2.8 and channel 40 is 1.7. We use most channels going from plant to plant and to different pits so I set the swr on 20 checked on 1 and 40 and also tested on 1 and 40 those are the readings I got. From what I read my antenna is short. I should add a spring to get added height and that would help with it being more flexible. With those reading and this antenna being 3 feet tall how tall of a spring should I look at getting? This is for a barjan antenna. The other thing I noticed is that when the meter was hooked up and I cal. I tried to move the cal knob on the radio and the needle on the meter didn't move is that I would like to keep my old stud and mount that is a 3/8" X 24 what would be the easiest to tune? I am thinking of buying the wilson FGT4 antenna with the tuneable tip and the better NOAA coverage that be a good choice? Thanks again!

    - Zachary140

    Last edited by zachary140; 01.11.2011 at 07.07 PM.

  2. #12
    Medium Load Member handlebar's Avatar
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    Zachary,
    You've got a couple of issues going on, and I'll address the ones I have enough info for.
    One, which you discovered by getting the external SWR bridge, is that your antenna is too short. Adding a spring will help; the 3- or 4-inch medium duty ones will be fine. They have a piece of braid on the inside so that the electrical length doesn't change as the spring flexes; otherwise the antenna would seem longer when it flexed.
    Once the spring is installed between the mount and the antenna, check SWRs again. If they're lowest around Ch 20, you're golden. Even at 2.0:1 (please note that it's a ratio, ALWAYS expressed as "to one") you're only losing 11% of your signal, and any normal final stage can handle that.
    Except that yours has been doubly handicapped. You mentioned that you paid for a "peak and tune", which usually entails clipping the audio limiter (thankfully not in your case) and squeezing another watt or two out of the transmitter. The factory tuneup calls for adjusting for peak output, then adjusting down to 4 watts without modulation, where the final amplifier transistor is not straining. Guess what happens at a "peak and tune"?
    Yup.
    And nobody will ever hear the difference, until your final transistor dies an early death from the added heat it makes from making that extra power, and you're off the air.
    The antenna warning light ("AWL") just samples a small portion of your power output, kinda like the RF output meter on the panel, and the SWR function that's built in -- this just samples the "reflected" side.
    A by-product of turning up the output power is that, even if the SWR is mostly OK, there's still more power being reflected. Under normal circumstances (with stock tuning) that would mean that the antenna system had failed. In this case, the AWL circuit just sees more energy and turns on.
    Remember all that heat that the final is making? It's supposed to be dissipated by thermal grease between the mounting tab and its insulator, and between the insulator and the heat sink. In the Cobras made since the late 80s, the factory no longer puts grease on the heat sink side.
    So even without the peak and tune, the transistors die early -- just usually not until the warranty period has expired.
    So -- (finally!) you can adjust the AWL threshold by turning VR6 while transmitting with your antenna hooked up, *once it's tuned*. But make sure it still comes on with no antenna hooked up.
    A lot of shops don't even have proper signal generators, so they don't even touch the receiver tuning.
    FWIW, I use a 2-ft Barjan on my service vehicle so I can fit into the garage, and typically get 10 miles with a barefoot Cobra 29 that's been correctly aligned. Out on the road, out of town, I switch to my sidemounted stainless 102" whip & spring.
    Hope that helps,
    -- Handlebar --
    P.S. I've been doing this over 30 years
    Last edited by handlebar; 01.15.2011 at 11.45 AM. Reason::  

  3. #13
    Medium Load Member handlebar's Avatar
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    Zachary,
    By the way, as antennas go, the longer and higher mounted, the better. Think of the antenna as a sail trying to catch wind.
    And the shorter the antenna, the bigger the difference a fixed length change (like a spring) will make, and the tinier pieces you have to nibble off a fiberglass antenna's windings to make.
    -- Handlebar --

  4. #14
    Bobtail Member
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    I purchased a firestik FL-4 their 4 foot flex antenna along with a new stud, and the heavy duty spring last night so that will help a lot. It should be here by next weekend The antenna is mounted as high as I can get it, and no cutting of the antenna with my adjustable antenna...even better....

  5. #15
    Medium Load Member handlebar's Avatar
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    Way cool! I've just found this forum, and it looks like every once in awhile I'll find a post where I can contribute a little something for the other users here.
    Please let us know how it works. When you adjust the VR6 after tuning the antenna (nice!), turn it till it just goes out on transmit with normal voice. Then disconnect the coax from the radio, transmit briefly, and confirm that the AWL comes on again. A few seconds at a time into an open circuit won't kill anything.
    See ya,
    -- Handlebar --

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  7. #16
    Bobtail Member
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    Got everything on the truck High SWR

    My cobra 29 WX NW BT has been installed for a while now but I was not using it due to higher swr readings. I ordered antenna parts from firestik all of these are firestik items. I got one four foot flex antenna (FL-4), one heavy duty spring (SS-3H), and one stud (K-4A). I installed everything. I changed my ground to ground only to the hinge area of the truck, and I got really high readings. Ch.1 was at about at the red line for calibration ch.20 a little under the calibration line ch.40 more under the cal. line than 20. I decided that since all three were tested over 3.0 it was a ground issue. I moved the ground to one of the four mounting bolts and put it behind the bold side. I then used another short jumper to go from the hinge bolt to the dash frame. So with my two grounding wires connected I tried it again. After some messing around with the tunable tip I got readings as follows: ch.1 - 2.5 Ch.20 - 2.75 ch.40 - 3.25 tuned the tip more and got ch.1 - 3.0 ch.20 - 2.4 ch.40 - 2.9 made one slight adj. and got ch.1 - 3.1 ch.20 - 2.5 ch.40 - 2.9. My old antenna was a bargan 3' antenna no spring. I added a spring to this antenna and used the firestik 4' antenna. What seems to be the problem? I think my higher readings are from a grounding problem. Where should I go from here? I currently have a 10 GA. braided wire grounding right now, is that sufficient or do I need more? What should I use? This is on a plow truck and I donít want to stick too much more money into this.

    Thank you for your input,

    - Zachary140

  8. #17
    Medium Load Member Carolina Thunder's Avatar
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    Quote Originally Posted by zachary140 View Post
    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 donít 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 donít 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

    Quote Originally Posted by zachary140 View Post
    My cobra 29 WX NW BT has been installed for a while now but I was not using it due to higher swr readings. I ordered antenna parts from firestik all of these are firestik items. I got one four foot flex antenna (FL-4), one heavy duty spring (SS-3H), and one stud (K-4A). I installed everything. I changed my ground to ground only to the hinge area of the truck, and I got really high readings. Ch.1 was at about at the red line for calibration ch.20 a little under the calibration line ch.40 more under the cal. line than 20. I decided that since all three were tested over 3.0 it was a ground issue. I moved the ground to one of the four mounting bolts and put it behind the bold side. I then used another short jumper to go from the hinge bolt to the dash frame. So with my two grounding wires connected I tried it again. After some messing around with the tunable tip I got readings as follows: ch.1 - 2.5 Ch.20 - 2.75 ch.40 - 3.25 tuned the tip more and got ch.1 - 3.0 ch.20 - 2.4 ch.40 - 2.9 made one slight adj. and got ch.1 - 3.1 ch.20 - 2.5 ch.40 - 2.9. My old antenna was a bargan 3' antenna no spring. I added a spring to this antenna and used the firestik 4' antenna. What seems to be the problem? I think my higher readings are from a grounding problem. Where should I go from here? I currently have a 10 GA. braided wire grounding right now, is that sufficient or do I need more? What should I use? This is on a plow truck and I donít want to stick too much more money into this.

    Thank you for your input,

    - Zachary140
    Stop messing with the fiberglass antennas first thing and get yourself a metal antenna. With a fiberglass antenna, they can be a real pain in the butt to get set right when your running a 4 foot antenna but with a full size Wilson you have more of a tuning range and therefor are easier to set,although you may have to clip the length of the steel whip a few times to get it right. They also perform much better than a fiberglass antenna as well. You only want to balance the SWR reading from ch 1, 20 and 40,this way you dont have to check each channel.

    You also must understand that the red light and SWR/cal on that radio can be adjusted inside the radio and can be off,causing the warning light come on.

    I have seen guys mount a 102 inch steel whip to the front of the bumper,on the very bottom of the bumper on either side. Those antennas are very hard to bend so they take more abuse than any other antenna and work just fine. Just run as much coax as you need to get it to your radio, as long as you do it in 3 foot lengths,like 18,21,23 and so on.

    As far as your SWR readings. Anything under 2.0 is completely fine. I know you may not believe me but its true. The people that are listening to you talk can not tell the difference between a 2.0 SWR versus a 1.1 SWR so chasing the perfect match is a wast of time and neither readings will your radio. It's only when you get above 2.5 that your start running into trouble. Check this out. lets says you are using RG-8 coax with an SWR reading of 2.0 on 27.205 ( channel 20 ) with a 30 watt radio your losing 3 watts. with an SWR of 1.1 your losing 2 watts so you can see that the 1.1 match is a wast of time. You can go to this website and see for your self the affects SWR plays on the ammount of power that passes out your antenna with different SWR readings and different coax. http://www.ve3sqb.com/hamaerials/ocarc/

    You will also not hear a change in the way your radio receives with a 2.0 vs a 1.1.

    After saying all of that i think a better choice for you would be a Wilson mag mount antenna. Just sit in the very center of you roof,set the SWR by raising or lowering the whip or even clipping some of the length of the whip off and forget about it. The Magnet draws its ground from the body of the truck so you dont have to run any ground wires at all. If you cant get the SWR down in the center of the roof then just move the mount forward or backwards on the roof until you find a location that the antenna likes. They work great as well but they can be a little high in price.

  9. #18
    Medium Load Member Carolina Thunder's Avatar
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    OH......and dont use a spring. The only time you may need to use one is if you use a 102 inch steel whip. For some reason these antennas like the 6 inch spring and can be easier to tune your SWR in with one. When you use a spring on any other antenna it changes the total length of the antenna and will make getting your SWR down a real pain in the butt! When it comes to an antenna,they are built with the correct length in mind and if you add a spring to one you throwing that off which is why SWR problems are hard to solve.

    Also,a different antenna other than a fiberglass antenna may solve your grounding problems as well. Different antennas require more or less ground than others.

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  11. #19
    Medium Load Member handlebar's Avatar
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    Quote Originally Posted by zachary140 View Post
    My cobra 29 WX NW BT has been installed for a while now but I was not using it due to higher swr readings. I ordered antenna parts from firestik all of these are firestik items. I got one four foot flex antenna (FL-4), one heavy duty spring (SS-3H), and one stud (K-4A). I installed everything. I changed my ground to ground only to the hinge area of the truck, and I got really high readings. Ch.1 was at about at the red line for calibration ch.20 a little under the calibration line ch.40 more under the cal. line than 20. I decided that since all three were tested over 3.0 it was a ground issue.
    <mass snippage ensueth thusly>
    - Zachary140
    Zachary,
    I just reread the thread, and noticed you'd ohmed out the mount to ground, etc. How about from the stud to ground? When you put the mount together, is there any chance you used a metal washer between the stud and the bracket on the top of the bracket? Here's what the mount should look like. That nylon washer has to be where it is, or the antenna will be shorted dead to ground, and you'll get high SWRs regardless of where else you put the intended grounds.
    Just a thought,
    -- Handlebar --
    Last edited by handlebar; 02.09.2011 at 09.31 AM.

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  13. #20
    Bobtail Member
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    I do not want a magnet mount antenna as I would not install one on my vehicles, nor would I install one on the company vehicle. They don't fade the rest of the vehicle like the bottom of the mount, they are very temporary and in my opinion they just don't look nice. I called the shop that I bought my antenna supplies from told him my swr was high and that I have everything grounded properly. He asked what vehicle this was on, and how long of a coax I had. I told him it was a 9 ft. coax and he said that was my problem. I asked him if the spring would have any effect to the height of the antenna and cause high swr readings and he said that he has a spring on his and his swr is good, and that it is because I have a 9 ft. coax. So this is where I am stuck at. I want the spring on there to help flex when I am going to the very low clearance asphalt plants that are approx 11 1/2 ft. tall. I don't want the antenna to get abused too harshly, thats why it is on there. I also see the point of having the spring on there makes the antenna longer and harder to get lower swr's. So what is fact and what is fiction? I have read multiple places that it doesn't matter how long the coax is. He also told me not to coil up coax because it would create a choke . You should coil it up and make a 1 ft. circle and squish it flat to make a 1 ft. thin oval. Is that the correct way to do that? I also called firestik and they suggested not to run the 10 GA. braided ground wire down from the mount to the hinge bolt, but to get a ground strap from the truck frame to the door to bypass the hinge instead Approx 6 to 8 inches. Does that sound like it would work better than the long ground wire (approx 3 feet)? It has been mentioned before about the ground acting as an antenna so I am thinking about doing away with the wire and bypassing the hinge. It may be the coax he says because there are many poor manufacturers who produce coax (I didn't see anyones name on it either). What are your thoughts on this at this stage.

    - Zachary140

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