cb radio trouble help...

i just installed a cb radio in place of my ash tray. i use 18ft of coax and mounted my wilson 4ft flex antenna on top of my bed topper which is fiberglass. i could get swr below 2 for a while then we decided to ground the a antenna straight to the coax cable and got and swr of 1.4. so i figure it was good to go and shortened the wires. after doing this my swr jump up far above 3 and im afraid to really mess with is for fear of burning up the radio.

any ideas where i should start?

 

you could get a non ground plane antenna so you will never have to worry about a ground (i went that route with mine).

i think you are going to need to ground the antenna to the frame, but make the ground wire as short as possible. i think there are some brackets around the bed of the truck that are attached (welded?) to the frame. if there is any paint at the point that you want to attach the ground wire to, make sure that you scrape the paint clear so that you see bare metal. you deffinately want a good ground connection.

good luck

 

well i was testing con tinuity and found that for some reason i have continuity between the positive and the ground in the plug for the coax cable.

 

well turn out thats not the issue cause my old multimeter has had it so i dont have continuity between ground and positive. and ideas as to why i can get my swr lower than 2.5???

 

Are there any other vehicles parked next to you while your testing your SWR? Sometimes the extra metal around you can mess with the readout on the meter. I usually try and check SWR's in an open lot. Make sure your ground is going to the frame.

 

It's wonderfully simple really.

1. Look at your antenna. It's called a "ground plane" antenna and what that means is that it's actually HALF of an antenna. The other half is a metallic ground, typically the metal roof of a car.

2. When you grounded the antenna straight to the outer jacket of the coax cable, you turned your cable into your ground plane - the second half of your antenna. This worked, because you had an 18' cable - which is a special length - exactly 1/2 wavelength of the CB frequency. Now, you had a full antenna. The wilson, plus the full cable length. Hence SWR 1.4

3. When you trimmed the cable to length - you broke your ground plane - it's a short random length, not 1/2 wave any longer. Now you don't have a full antenna any more!

So what's the solution?
Either ground the anteanna to the body via a short thick piece of conductive-cable, or replace your wilson with a "no ground plane" type antenna.

 

Good call. that makes total sense. learned somthing today! thanks

 

I'm amazed you got your swr to a 1.4 mounted on fiberglass. I always check my swr in wide open spaces away from powerlines and buildings. A 1.4 isn't bad. Of course 1.1 is a perfect match. But if your not running a high power radio it'll be ok. I had a Predator 10k antenna on the side of the bed rail of a 1997 Tacoma with plastic bedliner removed. It was 12" away from the back window. It wouldn't tune below 1.7. I had bare metal behind the mount and tightened all the stainless steel nuts. I was about to remove it when I decided to really tighten the nuts. And it dropped to 1.1 on chan 20. It was 1.3 on channels 1 and 40. I now am back to my Wilson 5000 on the roof since my new 2011 Tacoma has a plastic bed. Good luck getting a good ground there. I even grounding to the frame didn't help. Works perfect on the roof though.

 

i got it all sorted out. i lost the 1.4 swr and moved it to the bed and took my bed topper off. its around1.6 now.

 

wow Predator 10k huh? Thats a big antenna! what radio u using? I run that in my big rig with a slightly modified 200 watt radio (galaxy 94 hp)

 

If you mount to close to the glass, the Radiation out the antenna will bounce off the glass back to the antenna a give a higher SWR. I had mine mounted 12inches away from the back glass. Also if that's the same antenna you altered you might consider getting another. 4ft wilsons are my favorite fiberglass antenna. Not to short and looks better than the 5ft. Sometimes tuning a ground wire to the bracket doesn't help. If you need to. Then spend alittle extra a use a braided strap. Make sure everthings against bare metal. I put a little bit of dielectric grease on my exposed metal areas then bolt up tight.

 

Hey Jeepin456, I'm running a Magnum 257HP with a Texas star 500v. Always put your money into the antenna and the amp.

 

then maybe i can get my swr down if i move it away from the glass. didnt know that ill give it a shot and see what happens
oh yeah mine is a composite so i dont break it on a trail.

 

how far are you getting out? With my setup I am getting about 15 miles in town and 40 or so miles out of town in the desert but in good conditions and on top of a hill while talking to someone else with a good radio with them up pretty high I can get 70 miles or so. Linear miles of course.

 

Run the power wire straight to the battery and check your SWR it helped for me I run a cobra 29 classic made in the philippines into a TNT 12 pack puts out 1700 watts into a wilson 5000 works great

 

I might have to move mine since its mounted on the rail right behind the rear windows and my swr won't get below 6.0

Also, have you guys heard of only using coax in increments of 3' starting at 9', 12', 15'?

 

In my other truck. 1997 Tacoma I ran a General Lee with the new MOSFET finals set with 2 watt dead key for Texas Star 500v amplifier and predator 10k. I could talk 50 to 60 miles to my friend who ran base stations. With that setup , if I could hear you, I could talk to you. Mobile to mobile I seemed to max out at 27 miles. I did do 40 miles once on a mobile to mobile contact once. Condition were awesome that day. My current setup with the magnum 257hp a Wilson 5000 is doing 25 to 30miles barefoot(no amp) to my friends base stations. Haven't tested with the amp yet. It's getting a fan put on it. I can talk 10 mile to 15 miles easily with just the radio mobile to mobile. I will be drilling the roof for my Wilson 5000 to install roof mount. I miss my predator 10k. But Wilson 5000 ain't no slouch.

 

somehow I wanted to put a predator on my taco but I think it may look funny and would be easy target for theifs especially with the other equipment I have in my rig.

 

Every cb chop I have talked to and been in say that the best setup is 18 feet of coax. If there is extra coax it is to be coiled up in a loose figure 8 pattern and set aside. do not tie it down or together as it will interfere with the radio. If you cant get your swr were it should be which is 1- 1.5 ish then you have a bad ground, or bad antenna. the swr needs to be checked on the antenna itself and calibrated on the vbehicle if possible. The best place to mount and antenna is the middle dead center of your roof or the back of your truck at the tail gait. Others may be have their stories of how great their system is working and they have their antenna mounted near the cab however I can say that their sigal is lacking and not up to the best it could be if it were mounted where it should be. The only way to tell is to have an external swr reader available at radio shack for 15 or so dollars and take your antenna readings. You may have to regroung the antenna, remount it somewhere else, lenghten or cut some of the antenna in order to make your swr work for you. If you transmit on a high swr you will blow your radio....

 

Thanks for the info. I really think its my antenna but who knows. The external meter I have is the one that is reading high since the radio itself doesn't have one. I grounded it to the frame but still no go. Even grounded it to the battery and nothing. I will try a different mount position today. And I'm not to sure about cutting the antenna since it is a tunable firestik.