CH Mack and high SWR

Its possible the only ground you have is coming from the hinge, and makes contact only when the door is open. Their are other possible reasons why, but more important question is if it has a ground while closed? check with coax disconnected using DVOM

 

Thanks thedude, I'm just a novice cb radio trucker. I know very little when it comes to ground plains and running ground wires. I got my swr's down to around 1.3 to 1.5 with the door closed now, I just changed out the antenna but that stupid light on my cobra cb is coming on but my swr's are nice and low now. not sure why the idiot lights on?

 

When I first started driving oh about 10 plus years ago my company had me drive a 2005 Mack Granite Tri-Axle Dump so I purchased a real nice Connex 4400 Hp Cb Radio and a Wilson 2000 trucker Antenna which I mounted to the driver's side Door Mirror Bracket with a over sized Bracket because the pipe wasn't your normal size pipe and the regular wouldn't fit. Not knowing much about Cb Radio's I was under the impression all you had to do was hook it up and you were good to go. The Radio worked great for the better part of 6 month's, then I started getting Issues with people not hearing Me, one minute it work fine but hit a bump in the road it go out again or the Radio would not receive, hit a bump and it work till you hit another bump. So I took it in and found out I blew a final and the guy told Me I needed to Ground the antenna because My Swr's were way to high and you couldn't get them lowered by simply adjusting the Antenna. He told Me to get 10.0 Gage grounding wire run it from the bracket to the door hinge then again run another wire to the Hinge to the frame of the truck.
The main problem with these newer Mack trucks not having a good ground is the design of the Mirror Mount that holds the Mirror to the Door. The pipe is bolted to this Mount which is not made of Metal and thus makes the Mirror pipe and everything attached to it un-grounded! I ran a wire from My Antenna Mount bolt to the back of the bolt that holds this un-grounded non-Metal bracket, which makes contact with the Door.
For one reason or another I changed trucks and had to do the same procedure again till I was giving this New 2012 Mack Pinnicle day cab which I might add came with preinstalled coax duel cables and 2 black cb Antenna's. Figuring this is a professional set up by Mack I assumed it be fine so I installed My Connex Radio and everything worked just fine for the first Year. My Radio started acting up again where is it would work fine till you hit a bump in the road and you wouldn't receive then hit another bump and it work again. I purchased a cheaper model a Cobra 29 classic that has a red light that comes on when the Antenna has a problem. if the light don't come on it's working good but if it does you need to check your connections. After a year or so of every day service the light is back on so I check the Antenna on the Driver side it seems ok. I check the one of the passenger side and that's when I noticed a problem. Got My Swr Meter out and checked, was through the roof real high swr's but I mistakenly forgot to shut the Door and My Swr's went down to normal so I was pleased by this put everything away and closed the door. checked it again with the built in swr meter and it was through the roof again. I said wtf? so I dug out my swr meter again and tested it, yep the swr's are through the roof again with door closed. Not having grounding wire or a replacment Antenna I decided to use My spare Wilson Magnet Mount Antenna, I figure you don't need to Ground one of them they are already grounded by way of the Magnet. I connect it, place the Antenna on My roof and run the cable through the door, test my swr and it's again through the roof. Wtf? I open the door and it's fine. Hmmmm wtf? I can't exactly run down the road with My Door open can I ? Nope lol....
I'm thinking now the cab is not grounded properly and I need to ground it so I go out and get me some wire and followed the procedure above and then tested again using the original factory installed antenna's but swr's are through the roof again till I decided to try something a little different. I put the grounding wire just under the antenna where it screws into the bracket. above the plastic washer and My swr's went down, way down "Perfect". Hmmm that's weird but it works so I went with it but now when receiving I sometimes hear other's but it's garble (Distorted). My Guess is I'm still not getting true good grounding and I need to rethink how I should go about grounding this thing properly. I'm no expert and it seems everything I do has been a failure. Maybe I should have a cb radio guy do it for me? Or get someones expert opinion on how to go about doing all this. I was under the impression the antenna's I have don't even need to be grounded so I'm stumped at what is going on here. Right now as I speak, I got my swr's down but the grounding wire is attached above the plastic washer. Maybe all I need is a new antenna? I don't know.....

 

Grounding above the washer is incorrect. It should be connected to the coax side of the antenna mount.

Save yourself a ton of headache, get a single bird perch/clamp mount, and some mini 8x coax to run your own antenna. The factory coax is garbage.

 

you may have to go with a no ground antenna kit or maybe try like a wilson trucker antenna (if your swr is high on 40) and start cutting the whip 1/4 inch at a time until you get close to your 1.0 match

 

thank you guys for your help, I think I finally got it right. swr's are nice and low and light went off. All i did was simply run a ground wire from the door hinge to the chassy hinge and it went off so I guess I'm getting better ground now.
thank you thedude, littleitchy & white wolf for your help
bundy199

 

I’m having the exact same problem with our Mack CH. I’ll take some pics this evening for you if you don’t mind helping me out.

 

wow, I thought I was the only one having issues with high swr readings on a new mack. 29lx with 2 firestik antennas, just hooked them up to mirror after using firestik mounts and got high swr, adjusted antennas and got readings around 2 but running the rf output test and antenna test and both fail. thought about running new coax through both mirror brackets but my patience is getting slim and now reading these threads I should try to ground the truck?