CB Radio Help

Discussion in 'General Discussion' started by Nole, Mar 31, 2004.

  1. Nole

    Nole New Member

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    I know someone out there can help me with this problem I have heard some cb talk around here before.


    I am trying to swr my cb radio and i am getting a really high reading on ch 40 (+3). On ch 1 it is about 3. i have a 48" whip with 18 foot of coax the cb is wired into the fuse box under the hood. please help I am out of ideas not that i had any in the first place.
  2. Shooter45

    Shooter45 *Administrator* Staff Member

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    Check for a good ground at your antenna mounting bracket. If that doesn't help, you may need to change the length of your coax.

    For more help check out One Stop CB Forum.
  3. Nole

    Nole New Member

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    thanks for the forward
  4. Hydra Shok

    Hydra Shok Member

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    Hey Nole, if your swr's are to high, you have to change the length of the antenna. An swr of 3 isn't too bad actually, but you can make it better. If you just have a metal whip you can either snip a little off of it at a time, checking the swr's after each snip of course, or you can get a shaft to make it a little longer. Make sure the doors are shut while checking, just like the vehicle will be while you are driving. Also make sure you have a good ground, it will squeal if you don't. Also make sure you have an inline fuse in the power line. 18 ft of coax is perfect, but don't loop the excess, it will cause an interference in the signal, just stuff it somewhere and let it fall where it may. Has the radio been tuned and peaked out? And do you have a linear amplifier? If you have a linear it is a good idea to run a wire from the case of the linear to the case of the radio, grounding them both to each other. Also if you have a linear, turn it off while you are checking the swr's. A goos site to check out is www.copper.com

    I have the Voyage VR 9000 in my dumptruck and I highly recomend it. It's basically a generic Galaxy 88 at half the cost. If you have any questions ask away, been fooling with these things for many years now. Here is a pic of my office too :D . By the way, look in the pic of my truck at the antenna. It's a Wilson 2000, and the longer shaft I was talking about is right below the blue cover. You can get them in different lengths too.

    Attached Files:

    Last edited: Mar 31, 2004
  5. Marlin

    Marlin *TFF Admin Staff Chief Counselor*

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    Back to what Shooter said, though, a good ground can go a long way toward settling the problem. I had a similar problem on the Toronado with the in-dash combination AM-FM-CB-CD-Tape. Once we made sure the ground was solid the SWR floated around .7-.9.

    Same is true for Ham Radio in the vehicle.
  6. Nole

    Nole New Member

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    where would be the best place for the ground. when i checked the swr i had the cb grounded to the alternator. the power coming from the fuse box under the hood. Where would be the best spot? The antenna is a groundless one, so would it help it i grounded it anyway? Thanks for the help so far.

    Matt
  7. Txquadhunter

    Txquadhunter Member

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    Any clean metal area on your truck should place a good ground. wiether it is the alt like you did, motor, cab and frame. all the places on a truck are grounded together. depending on how old your truck is and if your in a area known for rust it can cause bad grounds to places. mainly the cab. But where you placed your ground on the Alt. if you look you'll see the Alt. bracket is the main ground point for the battery. besure your ground wire is shiney clean and point grounded is also shiney clean.

    i'm not a big CB user but have hooked a few up. I usually hook stereo systems up. Where I draw main power for my Amp's is from the + side of the battery instead of the fuse box. The wiring and inline fuse rated at what it calls for to get the amps needed. this bypasses any interfence that can be picked up from other sorces at the fuse block.
    Last edited: Apr 1, 2004
  8. JohnK3

    JohnK3 New Member

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    Changing coax lengths does little to truly change the SWR of a transmitter/antenna combination. At best, it masks the problem.

    The trick is to make the antenna resonant at the chosen frequency, with a feedpoint impedance that matches that of the transmitter output. Change the length of the antenna to improve the SWR, as Hydra Shok suggested.

    First, you have to measure the SWR at various channels. Check to see if it gets better or worse as the channels get lower. If it gets better, then your antenna is too long. If it gets worse, then your antenna is too short. Remember, as your frequency goes up, the wavelength gets shorter.

    Grounding is absolutely a requirement for good SWR and reception. An antenna requires the ground to provide the other half of the signal. Unless you're running an odd-wavelength antenna, such as a half-wave or 3/4 wave whip, you need a good groundplane. An antenna attached to your mirror bracket won't have a good groundplane. An antenna in the middle of a good metallic hood or roof of the vehicle has a good groundplane. Grounding needs to be solidly to a major chunk of the vehicle. Ground as close to the transmitter as possible, using the heaviest gauge wire you can. I like to ground using fairly wide (1" or more) tinned braid. You can get this by taking a piece of heavy coax apart and taking the braided piece out and flattening it. Tin the ends using solder to keep it from unravelling.

    73 de W5NNH
  9. inplanotx

    inplanotx New Member

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    The grounds should be as close to the unit and antenna as possible. It should be grounded to the FRAME, not the alternator. Power should also be taken from a wire close to the radio where it has noise suppression. You can also go to Radio Shack and get a noise suppressor and put it on the power line to the CB unti. Power and ground as close as you can get it to the unit.
  10. JohnK3

    JohnK3 New Member

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    Actually, for least noise, run the power all the way to the battery, putting fuses as close to the battery as possible on both leads. Do NOT ground the negative power lead, run it to the negative terminal on the battery. Ground the transmitter from the frame of the transmitter to the frame/body of the vehicle with as short a lead as possible. IF the antenna has a spot to ground with (ie: non-magmount), then ground it to the frame with as short a lead as possible.
  11. inplanotx

    inplanotx New Member

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    Actually, this is something you want to totally avoid. This wire has to run from the front of the vehicle past the ignition system and alternator and then into the passenger compartment. A wire is nothing more than an antenna which will pick up any RF signal it passes near. It is called "cross talk". The 30,000 volts or even 50,000 volts if a newer vehicle, creates RF (radio frequency) which can be picked up by an antenna (wire). A battery is charged by the alternator which puts full wave rectified DC into the battery, but still has a small AC component. The smaller the wire used for power (12 volts, actually 13.8 to 14.2 volts if the alternator and regulator are working correctly) and ground the less noise induced into the electronics.
  12. JohnK3

    JohnK3 New Member

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    Hate to correct you like this, IPT, but this goes against everything I've been taught as an Amateur radio operator, what professional installers for commercial radios taught me and basic radio theory.

    By running both wires, IN PARALLEL, you actually avoid making one of them an antenna. For even better protection, give them a light (1 in 12") twist to help guard against the alternator noise.

    Any imbalance in a pair of wires makes the longer one become an antenna. Specifically, we call that form of antenna an "End-fed Zepp" from the way they used to use them by dangling ladderline out of the bottom of a Zeppelin. One of the sides of the ladderline would be attached to a long wire that was anywhere from 1/4 wavelength or longer for the desired frequency. The ladderline section acted as a matching section to bring the feedpoint impedance close to a match with the transmitter.

    Go do some research on the subject. I've done so. Even had to pass a test on it.


    From the General Class Amateur Radio License Examination Question Pool:
    http://www.arrl.org/arrlvec/El3-2000.txt

    G4E03 @G4E03 (A)
    Which of the following power connections would be the best for a 100-watt HF mobile installation?
    A. A direct, fused connection to the battery using heavy gauge wire
    B. A connection to the fuse-protected accessory terminal strip or
    distribution panel
    C. A connection to the cigarette lighter
    D. A direct connection to the alternator or generator
    Last edited: Apr 1, 2004
  13. inplanotx

    inplanotx New Member

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    Morning John, God I love a good exchange of information in the morning. Gets the ole brain cells moving. First off, lets start by talkin apples vs apples and thow away those dang oranges you are trying to compare that apple to.

    To start, let's do this. Since you are a general class license holder, it should be easy for you. Going back to 1965 - 66, look up license number WN2MNA and WA2IXF. The former, belonged to me with the following address:

    142 Fallwood Parkway, Farmindale, NY 11735

    The latter belonged to a Brother Brendan ... I forget his last name
    at the following:

    LaSalle Military Academy, Oakdale, NY

    That was a private high school I attended. The club used the WA2IXF call sign. It was an advanced station license.

    Next, we need to go to the State University of NY for 1976 and again look up my name (from the license) to see that I earned a BS in electrical engineering which I have been using ever since as a careeer.

    Okay, enough drivel. I understand about a high wattage ( 100 Watts as you pointed out) RF transmitter in a vehicle. Unfortunaltely this poor fella is trying to install an under 5 watt radio transmitter that in no way shape or form fits into the class of transceivers or transmitter/receivers that we play with. This is a dinky little play radio transceiver. Hardly worth the effort and both you and I know we would bypass in a heartbeat.

    Since, by law (FCC regs), that little toy is required to be under 5 Watts total output, if he runs heavy guage wire from both ends of the battery, he is not going to twist the wires 1 in 12" and he is just going to lay them side by side all the way into the passenger compartment. Except now that we are discussing this, he may have reservations. So, we now need to figure out the current to fuse this and pick the correct wire guage to mount it.

    P = IE 5w = I x 12 volts
    I = ~500ma = 0.5 Amps

    I would bet his in dash radio draws more current. So 16 guage wire should be more than enough. I have always worked by the KISS principle due to Murphy's law always showing up at the wrong time.

    Going back to your 100 watt transceiver, using the above formula, you come up with about 8+ amps. Now, that does draw considerable problems into the equation and since it is a factor of 16 times greater, presents it's own set of rules. We do not need to go there for this. Does not apply, 'D' all of the above! So no need to go your way. Using the KISS priciple, (Keep It Simple Stupid), the theory, not referring to anyone, we use as short a piece of 16 guage wire with a 3/4 Amp fuse and we are done.

    Not only have I participated in the enjoyment of Amateur Radio with you and passed my novice test which led me into electrical engineering where I had to pass many tests including a professional engineering test over many years, but I practice my career every day.

    I used to have both the 2 Mtr and 6 Mtr Heathkit lunchbox "put it together yourself" units, but the club has a Hammerlund HQ 110 receiver along with a Johnson Viking II transmitter along with a 24 watt 2 Mtr tranceiver. Had the longest QSL with the 2 mtr rig also. From NY to Virgina. We had a trap antenna on the roof and on a cloudy day I aimed at the water of the Great South Bay, where the school was and "skipped" the signal all the way down there! Pretty good feat in 1965-66!

    Always remember,

    Real Amplifiers























    Glow In The Dark!!

    Wanna send me a QSL card? Nice chattin with ya. Have a great day!
    Last edited: Apr 2, 2004
  14. Nole

    Nole New Member

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    well thanks for all the usefull info. I am going to try and work on it some on monday and try a differant setup with the wiring. hopefully thatll work out for me. Just one more question. I have the antenna mounted on the driver side of my truck right behind the cab on the bed rail. Is that a good enough spot for the ground plane? If not where else would be a better spot? You guys said it the best spot is on top of the roof but I cant bring myself to put it there since i am not going to be talking on the cb that much. Thanks for the wiring help. Now I just got to get the time to work on it.
  15. inplanotx

    inplanotx New Member

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    Nole, your antenna will radiate more to the opposite side and in the direction of the front of the vehicle. If it were placed in the middle of a car top, then it would give equal signal strength from front to rear and side to side. It is looking for the ground plane. Since you have very little to the drivers side and most to the opposite side and back, you will radiate that way. You are also killing yourself since the antenna is trying to radiate through the cab and hitting a ground plane. I think I'm beginning to understand why your SWR is so low. You are getting a reflected wave as the signal hits the cab.
    Last edited: Apr 2, 2004
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