Alright here is my question.

I have my Cobra 75wxst run with 18' coax to my 4' firestick. I have it running straight of the battery cause I like to be able to use it with the vehicle off. My antenna is tuned so that my SWR is <1.5 (most are right around 1.2) across all channels with the vehicle off. Now when I turn the vehicle on it jumps to 2.2-3.0 across all channels?? Do I need to change my ground location or do I need to get one of those ferrous rings for my power cable????? Thanks for any advise, I am still learning all this radio stuff.

 

First, I am not super-expert, but I have fooled around with CBs a bit. I would start with changing the grounding location since that is easiest and cheapest. Also, make sure the antenna cable is not run to closely to any other wiring or anything that might produce and eletro-magnetic field when the vehicle is turned on. This can be the fan motor for your air conditioning, dash board lighting, wiring under the hood, etc. If you can't reroute and eliminate the problem, then you probably need to shield your wire. Lastly, you might consider leaving it alone. For me, I only use the CB when I am on the trails. At those times I only need to talk to people in about a 1 mile radius. If your CB reaches as far as you want it to, who cares what the SWR is? Just a thought.

 

It is difficult to tell where you have the radio ground wire connected, but it sounds like the negative terminal on the battery. Remove it from the battery and connect it to the common ground point on the chassis just ahead of the battery. You can't miss it, there are several other ground wires connected there. If this doesn't solve the problem, give consideration to also grounding your antenna mount to the chassis. I grounded mine to the right rear seat-belt bolt the is attached to the floor of the tub. It lowered my SWR readings from 3 to 1 across the board. Are you using crimp-on wire connectors at the attachment points to the battery and chassis?

 

Your right, it is on the battery, I will move it to the common point. I did use crimp on connectors at the battery but I soildered them on for a good connection. I guss if those two things dont work I will try grounding the antenna as well.

 

I've gotten to where I don't hardly use my SWR meter anymore. All you need to do is make sure your coax hot (center) and ground (shield) have no continuity. I just use a volt/ohmmeter and ground the antenna shield. I make my final check with the meter to mak sure there is no continuity whatsoever, and let her fly. Now, since these newer adjustable antennas have come out like the Firestick, you can adjust the SWR some, but if you have a shorted or ungrounded coax, no amount of antenna adjustment in the world is gonna get you in the ballpark. The adjustment on the antenna is simply for fine tuning. And make no mistake.....that adjustment on the antenna does not actually CHANGE SWR at ALL. All it does is fool the meter into thinking it changed.

 

Don't ground the antenna - ground the antenna mount. Here's a lesson, from personal experience, on setting the SWR on a Cobra 75. Due to the unusual setup of the 75, what you are connecting the SWR meter to is the 75's junction box and the antenna. The antenna lead is usually short, about one foot as is the dual male connector lead that connects the output of the radio, via the junction box, and the SWR meter. I spent the better part of an afternoon trying to figure out why I couldn't get a reading under 3:1. And then, as I was looking in my lap, where I had both the SWR meter and the junction box actually touching each other, I figured out that the 12V power line coming from the battery to the junction box was feeding over into the SWR meter and driving the readings off the meter to the right. So I separated the SWR meter and the junction box as far as I could, about one foot. It made all the difference in the world. The readings immediately came into range and I ended up with (1) 1:1, (20) 1.2:1 and (40) 1.1.

 

Connecting your radio directly to the battery, positive and negative is the best, very best possible way to install a radio in a vehicle, minimizing engine noise to the radio. As the jeep is sitting still, off, your battery is probably sitting at 12.0 to 12.8 volts. When the engine is running the battery is probably sitting at 14.4 volts. The more voltage you give your radio up to a certain point of couse, the radio will produce more wattage output, to its fullest (cb is about 5 watts). This is why you have a higher VSWR reading when the engine is running. Like others have said, tune your antenna the best that you can and thats probably the best your gonna get, providing you have a good ground to the antenna.

 

Thats why I was asking about the ground. With my engine turned off my readings arent much higher than yours, but when i have the JK running and test my readings are near to 3:1 across the board?

 

I'm sorry, but this is just not correct. Literally everything electrical on a vehicle is either hot or ground. With the CB antenna, there's no difference. The coax center is hot and the shield is ground. The shield from the coax MUST be grounded AS WELL AS the shield portion of the antenna. Grounding the mount does absolutely nothing. I see people scraping paint off mounts to ground them. It's just not necessary. If you throw the mount into the ground circiut, then you have one more thing to get rust dirt and debris into and lose your ground connection. If you ground the shield directly to the vehicle chassis and bypass the mount, you eliminate that possibility. ....and no, the mount doesn't need to be in the "ground plane" loop, either. What's the mount measure? 2"x3"? ooooo what a ground plane!!! RF doesn't care, it will use the Jeep for the ground plane. That's how it works. The mount has not ONE thing to do with how the CB works electrically. Not ONE. As long as the shield is ground and the coax center is hot, you can stand next to the Jeep with the antenna in your HAND and it will work just the same.

 

There you go agian, and again I will call BULLSHIT...!!! The adjustment of an antenna, ie, to lengthen, or shorten it, is in direct relationship as to how the antenna radiates to the desired frequency. It has EVERYTHING to do with SWR. Yes, you cannot have a direct short in the system, (hot and shield cannot touch) but to say that it doesn't make any difference how long an antenna is, and it's only fooling the meter, is dead wrong. On some antennas just the difference of 1/8 to 3/4 of an inch, especially on these little mobile antennas, can mean a 1.1:1 or a 3 standing wave ratio. AN SWR meter doesn't just read if you have problems with your coax or ground, it reads the WHOLE matching antenna system as well.