Good Cb Antenna Ground

[3King]

Going to try and make this simple.

3 weeks ago I installed a little Uniden pro 505xl radio in my truck with a 2ft Wilson tunable antenna. Didnt need anything special to begin with. Anyway I had my SWR at 1.1-1.3 on 1/40. I text a buddy of mine and had him get on his radio that lives 14 miles away from me. These little antennas are only suppose to get 1-3 miles. But I got 14.5 miles of range with a great tune. I mounted my antenna on the bed of my truck. However, A few days later I took the antenna off and had my truck bed Line-x. Put my antenna back on the bed in the same spot that I had sanded to bare metal, SWR is through the freakin roof. Is this because of my bed being line-x’d? I want to try to keep my antenna in that same spot, Is there any way I can make a better ground in that spot? Or is my best move to mount it on the front driver side of my hood/fender. There is one guy on YouTube that has his 2ft antenna bolted to his truck bed and his truck is sprayed on liner. So not sure why he would have such good SWR and mine won’t go below 3 ha. Any ideas would be greatly appreciated.

 

[mmckenna]

The bed liner shouldn't make a difference if the antenna mounting bracket is bolted through and making good electrical contact.

Something changed, either the coax got wet, something is no longer making good contact, etc. Go through your system with a multimeter making sure something isn't shorted, your ground connection is good, etc.

 

[mmckenna]

I'd probably start by connecting that ground lug to the bolt that holds the mounting bracket to the truck bed.

 

[3King]

The bed liner shouldn't make a difference if the antenna mounting bracket is bolted through and making good electrical contact.

Something changed, either the coax got wet, something is no longer making good contact, etc. Go through your system with a multimeter making sure something isn't shorted, your ground connection is good, etc.

I also changed out the coax cable and redid my ground wire. Everything is the same as when I first hooked it up. I have it grounded to the amp in my truck. Which that is how it was when I got such low swr. Mounting bracket is in the same spot. I did sand it down a little more after I got my truck back. Radio hasn’t move or been messed with.

 

[mmckenna]

I also changed out the coax cable and redid my ground wire. Everything is the same as when I first hooked it up. I have it grounded to the amp in my truck. Which that is how it was when I got such low swr. Mounting bracket is in the same spot. I did sand it down a little more after I got my truck back. Radio hasn’t move or been messed with.

OK.
RF ground and DC ground are different things. You want that wire grounded to the mount.

 

[3King]

OK.
RF ground and DC ground are different things. You want that wire grounded to the mount.

Ok. So the wire coming off the antenna I should ground to the mount it self instead of my amp in my truck.

 

[mmckenna]

Ok. So the wire coming off the antenna I should ground to the mount it self instead of my amp in my truck.

Yes. You want it as short as possible.

 

[3King]

Yes. You want it as short as possible.

ok. Weird that it would do that now, And when I first hooked it up, I had it connected to my ground on my amp in my truck.

 

[WB9YBM]

I might go a step further by making sure there's a good electrical (not just mechanical) connection between:

• battery to chassis
• truck bed to chassis
• panels to chassis
• hood to chassis
• etc.

using one common point (or points as close together as possible) to avoid ground loops.

 

[prcguy]

Question, does the antenna have its own flying ground lead that comes from under the black heatshrink at the base of the antenna? If so the connection point of that wire to the vehicle is probably critical to tuning.

Any CB or HF antenna mounted along the top of the narrow bed wall is going to be an insufficient ground plane and will usually not tune up if at all. The antenna needs lots of flat sheet metal under it as a ground plane and a grounding wire back to the radio or battery has nothing to do with an antenna ground plane except that the wire coming off the mount towards the radio or battery can be considered a ground radial. The actual connection to the radio or battery at the far end is insignificant and will not change or improve anything.

Look at the antenna as an island and you want the island as big as possible with as much sand around it as you can get. In this particular case, since the bed rail is an inadequate ground plane the coax back to the radio becomes part of the ground plane as does the black wiring coming off the antenna. If the coax path or black wire path has changed since the bed liner went in, like its tucked in against the sheet metal of the bed, then the ground plane has changed and the antenna tuning will be different.

As a test you can temporarily clip a long piece of wire to the ground side of the antenna mount and stretch it out like a ground radial away from the truck and check the match. I'll bet its improved or its very good. Then remove the wire and the match will go back where it was. This will prove or disprove there is not enough ground plane and you can then find ways to make it better. You can even run a wire or two from the antenna mount across the bed opening and attach to the other side of the truck. It wont be good for loading stuff in the bed but the antenna will be much happier.

 

[3King]

I might go a step further by making sure there's a good electrical (not just mechanical) connection between:

• battery to chassis
• truck bed to chassis
• panels to chassis
• hood to chassis
• etc.

using one common point (or points as close together as possible) to avoid ground loops.

I just grounded the antenna to the mount. Ran the SWR, still sky high. I made sure the spot where the mount is bolted to bed is good bare metal. It is, Everything is the same as what it was when I first hooked it up. For kick n giggles I’m gonna move it to the front of the truck and see what happens. If I still get high swr, I won’t know what to try.

 

[3King]

Question, does the antenna have its own flying ground lead that comes from under the black heatshrink at the base of the antenna? If so the connection point of that wire to the vehicle is probably critical to tuning.

Any CB or HF antenna mounted along the top of the narrow bed wall is going to be an insufficient ground plane and will usually not tune up if at all. The antenna needs lots of flat sheet metal under it as a ground plane and a grounding wire back to the radio or battery has nothing to do with an antenna ground plane except that the wire coming off the mount towards the radio or battery can be considered a ground radial. The actual connection to the radio or battery at the far end is insignificant and will not change or improve anything.

Look at the antenna as an island and you want the island as big as possible with as much sand around it as you can get. In this particular case, since the bed rail is an inadequate ground plane the coax back to the radio becomes part of the ground plane as does the black wiring coming off the antenna. If the coax path or black wire path has changed since the bed liner went in, like its tucked in against the sheet metal of the bed, then the ground plane has changed and the antenna tuning will be different.

As a test you can temporarily clip a long piece of wire to the ground side of the antenna mount and stretch it out like a ground radial away from the truck and check the match. I'll bet its improved or its very good. Then remove the wire and the match will go back where it was. This will prove or disprove there is not enough ground plane and you can then find ways to make it better. You can even run a wire or two from the antenna mount across the bed opening and attach to the other side of the truck. It wont be good for loading stuff in the bed but the antenna will be much happier.

ok. So the only thing different I did was run the coax cable through a little hole at the bottom of the back wall of the bed, Rather than run it up and over the top of the bed between the cab/bed. Other than that. Everything is the same, Except I changed out the original cable because I thought maybe the cable had gone bad randomly. Attached photos.

 

[prcguy]

So the original setup had a bunch of coax exposed, run in the clear and that acted like a ground radial. When you tucked it in a hole in the sheet metal you choked it off and lost some of your ground plane and detuned the antenna. Do the temporary wire trick I mentioned above and make a ground radial then check the match. You need to know the cause of the bad match and that will clue you in.

ok. So the only thing different I did was run the coax cable through a little hole at the bottom of the back wall of the bed, Rather than run it up and over the top of the bed between the cab/bed. Other than that. Everything is the same, Except I changed out the original cable because I thought maybe the cable had gone bad randomly. Attached photos.

 

[3King]

So the original setup had a bunch of coax exposed, run in the clear and that acted like a ground radial. When you tucked it in a hole in the sheet metal you choked it off and lost some of your ground plane and detuned the antenna. Do the temporary wire trick I mentioned above and make a ground radial then check the match. You need to know the cause of the bad match and that will clue you in.

Yeah I moved the coax cable back to run up and over the bed between the bed and cab of the truck. I will get the SWR in a few mins. I have to head to an appt. I’ll let you know.

 

[mmckenna]

And, I know this isn't what you want to hear...
This is why so many of us insist on putting our antennas dead center on the roof of the vehicle. Most antennas require a ground plane under the to work properly. Trying to skip the ground plane results in poor performance.

 

[jhooten]

That wire coming off the antenna is a DC ground for the purpose of bleeding static build up from the antenna. It should have no effect on tuning.

 

[mmckenna]

Depending on the type of coil they use, it may be required. Looking on line, I can find any information that says if this is a simple loaded 1/4 wave, or if it's a 1/2 wave or 5/8 wave.
Photos I find show that lead grounded to the mount.

 

[3King]

And, I know this isn't what you want to hear...
This is why so many of us insist on putting our antennas dead center on the roof of the vehicle. Most antennas require a ground plane under the to work properly. Trying to skip the ground plane results in poor performance.

i checked my SWR again with the cable running how I originally had it, Up and over the top of my truck bed. Still over 3. Ha

 

[mmckenna]

This is the point where a multimeter and the skills to use/read it will help out. Something has changed. Might be damaged cable, might be a failed connector, might be an improperly assembled antenna base. You need to troubleshoot your system and find the fault.

 

[prcguy]

I've only seen static build up on a mobile whip during blowing sand in the desert and maybe doing 60mph during a fluffy snow storm. Any ground wire built into a whip is for matching purposes.

That wire coming off the antenna is a DC ground for the purpose of bleeding static build up from the antenna. It should have no effect on tuning.