SWR Help

I'm driving a Volvo vn670. I'm planning to mount an aftermarket antenna and I hear you have to be sure the antenna is grounded. I'm going to try a Volvo mounting bar, rather than clamping it to the ungrounded mirror.

Have someone check your antenna ground if you can't do it yourself.

 

My brother drives a Volvo (a 2010 I think) and uses the bird perch on the mirror. He has a 4.5ft Francis, 9ft coax and a perfect SWR.

Might check the coax. Could even be the antenna. It is a good idea to periodically clean and shiny up all your metal to metal contacts. Running a ground wire will probably not change anything. You are not looking for an electrical ground, you looking for a RF ground. Running a braided strap (you can use coax. solder the center conductor to the braid) will solve the problem usually. Keep your runs short, 18 inches or so. Run one from the antenna mount to the door, or in your case you might start from the door to the truck body (across the top hinge). Then go from the body to the frame. The bigger (more surface area) the braid strap the better I think. I like to use the flat braid stuff.

 

The perch mount actually mounts to the cab just above and forward of the door. It goes into one of the mirror bracket mount holes. So the door grounding might not be part of his issue. Not sure. I wold double check the mount to make sure it is tight etc. An ohm meter would help to see if the bracket is actually grounded. Or even a test light. Hook the ground side of the test light to the bracket then touch the prob end of the light to the positive post of the CB power hook up. Just unhook your antenna coax first so that it does not see a ground through the CB.

Another possibility is that the antenna is simply too long. Pull the stinger and cut 1/4 to 1/2 inch off the bottom and put the stinger back in and double check the SWR. I had the same issue with my wilson 5000 and had to cut more then an inch off the bottom of the stinger before my SWR would go down across the board. Once I got close then I could see the difference in SWR between channel 1 and channel 40.

But if you have an ohm meter then check for continuity in the chassis ground then check the coax to make sure you have continuity at the center of the coax from end to end then check for continuity at the outer ground section of the coax (outer part of the connector) from end to end then check to make sure you do not have continuity between the center and the outer part of the coax.

Also do you have the 5 inch shaft wilson or the longer shaft version and is your volvo a condo or a mid roof etc?

 

Well, the good news is that at 2.5 you will not cause any damage to the radio. It just will not be operating at an optimal level.
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When you tried everything and the SWR will not lower, that is a dead giveaway that the antenna ground plane is insufficient. Your goal is to interconnect the large metal surfaces or "bonding" (door, door frame, cab and frame) to become as one large antenna ground plane. This is done for RF [radio frequency] purposes and has nothing to do with electrical grounding or the electriral circuit. In simplest (gross over simpification) terms the antenna ground plane allows the cb radio components to perform at their best. Please keep the lengths of wire short to prevent the wire from acting like another antenna. Do not run a long length of wire or ground strap. Use multiple short lengths to interconnect antenna mount, door, door frame and chassis.
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Using an ohm meter on the lowest scale, check the resistance between the outside of the antenna mount and the bolt that connects the door to the upper door hinge. It should read zero. If not, run a ground strap or 8/10 gauge wire from the antenna mount to the upper door hinge on the door side.
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Next using an ohm meter on the lowest scale, check the resistance between the outside to the antenna mount to the upper bolt that connects the door hinge to the door frame. It should read zero. If not, run a ground strap or 8/10 gauge wire from the bolt that connects the door to the upper door hinge across to the upper bolt that connects the upper door hinge to the door frame. This should appear that you are shorting around the door hinge. Recheck from antenna mount to door frame.
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Using an ohm meter on the lowest scale, check the resistance between the outside of the antenna mount to the lowest bolt that connects the door hinge to the door frame. It should be zero. If not, run a short ground strap from the bottom bolt that connects the top door hinge to the door frame to the top bolt the connects the bottom door hinge to the door frame. Recheck from the antenna mount to the bottom door hinge.
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Again using the ohm meter on the lowest scale, check the resistance between the outside of the antenna mount to the chassis frame. This should be zero. If not, run a short length of ground strap or 8/10 gauge wire from the bottom bolt that connects the bottom door hinge to the door frame to the chassis frame. Recheck from antenna mount to chassis frame.

 

I would say you do not have a good ground plane or the mount does not provide a good ground to the truck chassis. Check the connection on the stud mount as well. Is the nylon washer seated properly or installed properly?

 

http://www.firestik.com/Tech_Docs/Mnt-Grnd.htm

 

is this the same mount?

 

The mirror is mounted to the door on my brother's truck, 08 Volvo. I just talked to him and he said there is a 1/4 inch wide, braided wire, that runs back into the door, but he has never checked to see where it goes. But he does have a good SWR on that truck.

 

Then I was wrong. Been a while since I have been in a Volvo.