Getting a good ground on CB antenna mount

[Gblabla]

Having read several threads on CB radio installs I totally understand the importance of having a good ground from the antenna mount. I'm going with the Teraflex taillight mount but have a problem as my Sahara has the tail light protectors installed and there is a layer of dense foam between the mount and the body.

So what is my best option for ensuring I get a good ground? If I clear the paint on the bracket from the upper mount bolt (where there is no foam) and body will that be enough of a ground through the bolt? If not, how could I run a ground strap? Any other suggestions from those that may have faced this issue?

 

[reddvltj]

Having read several threads on CB radio installs I totally understand the importance of having a good ground from the antenna mount. I'm going with the Teraflex taillight mount but have a problem as my Sahara has the tail light protectors installed and there is a layer of dense foam between the mount and the body.

View attachment 126658

So what is my best option for ensuring I get a good ground? If I clear the paint on the bracket from the upper mount bolt (where there is no foam) and body will that be enough of a ground through the bolt? If not, how could I run a ground strap? Any other suggestions from those that may have faced this issue?

It would be fairly simple to run a ground wire along the coax and attach it to the mount, giving your mount it's own separate ground.

 

[Tscott]

It would be fairly simple to run a ground wire along the coax and attach it to the mount, giving your mount it's own separate ground.

That'll work too but again, where you attach the wire to the bracket can't have any paint. Also, keep the wire as short as possible. I learned this the hard way and it didn't work well.

 

[reddvltj]

That'll work too but again, where you attach the wire to the bracket can't have any paint. Also, keep the wire as short as possible. I learned this the hard way and it didn't work well.

If it were me I would tap this little hole and attach the ground wire there. A 12 ga wire run from there to the closest possible ground along which ever way you route your coax should work fine. That way you're not having to scrape any paint off the body tub.

 

[Jerry Bransford]

There are grounds, which are easy to provide, and there are RF grounds which are vastly different and far more difficult to achieve. Far more difficult. An Ohmmeter will not tell you if you have a good RF ground, it'll only show if there's a connection or not. A BAD RF ground can still show a perfect 0 Ohm connection on an Ohmmeter.

Wires are useless for RF grounds, you need to use braided ground straps. RF needs a large surface area to travel on and braided ground straps provide that large surface area RF needs. Wires don't, not even big 10 or 12 gauge wires.

Scraping paint between connection points is usually needed and if you can't get that done well enough, then it's time to add the braided ground strap to assist in providing the crucial RF ground.


This is a braided ground strap, electronic stores like Fry's, Radio Shack, and ham/CB radio stores carry them.

Depending on your antenna mount, this will help if it's the more common SO-239 style which is my preference. I added a few tidbits here and there on the illustration. And make no mistake, the "Insulated Shoulder Washer" shown below and its proper placement is CRITICAL. If it's not present, if it's in the wrong position, if it's not centered in its hole, or if it's broken you won't be able to tune the antenna. Oh, leave the powder coating INSIDE the hole that the SO-239 sticks up through, the powder coating is only scraped away from a bottom horizontal ring around the hole so the hex-shaped surface (located below the mounting bracket) of the SO-239 can ground to the bracket.

 

[tworley]

Put the bracket between your taillight guard and the body. Scuff up the body and mount to bare metal, that will be a good solid ground

 

[Tscott]

There are grounds, which are easy to provide, and there are RF grounds which are vastly different and far more difficult to achieve. Far more difficult. An Ohmmeter will not tell you if you have a good RF ground, it'll only show if there's a connection or not. A BAD RF ground can still show a perfect 0 Ohm.

I stand corrected. Thanks Jerry.

 

[Gblabla]

There are grounds, which are easy to provide, and there are RF grounds which are vastly different and far more difficult to achieve. Far more difficult. An Ohmmeter will not tell you if you have a good RF ground, it'll only show if there's a connection or not. A BAD RF ground can still show a perfect 0 Ohm connection on an Ohmmeter.

Wires are useless for RF grounds, you need to use braided ground straps. RF needs a large surface area to travel on and braided ground straps provide that large surface area RF needs. Wires don't, not even big 10 or 12 gauge wires.

Scraping paint between connection points is usually needed and if you can't get that done well enough, then it's time to add the braided ground strap to assist in providing the crucial RF ground.


This is a braided ground strap, electronic stores like Fry's, Radio Shack, and ham/CB radio stores carry them.

View attachment 126675

Depending on your antenna mount, this will help if it's the more common SO-239 style which is my preference. I added a few tidbits here and there on the illustration. And make no mistake, the "Insulated Shoulder Washer" shown below and its proper placement is CRITICAL. If it's not present, if it's in the wrong position, if it's not centered in its hole, or if it's broken you won't be able to tune the antenna. Oh, leave the powder coating INSIDE the hole that the SO-239 sticks up through, the powder coating is only scraped away from a bottom horizontal ring around the hole so the hex-shaped surface (located below the mounting bracket) of the SO-239 can ground to the bracket.

View attachment 126676

Thanks Jerry for summarizing exactly what I need to do. I will be going the route of the ground strap as I really don't want to scrape paint off the body and even then I'd have to run the mount on the backside of the light protector which would look pretty bad. I am using the SO-239 and the mount already has the powder coating removed right where the hex nut coax connector goes.

If I scrape off the powder coating around one of the mounting holes on the mount itself and run the ground strap from there (between the light and the mount) into the inside of the Jeep and find a clean - paint free place to attach the ground then I should be good to go - Right?

 

[reddvltj]

This is directly from Firestik
"The ground problem should not discourage you from using one of these convenient mounting locations. All you need to do is to run a short (as short as possible) ground wire from the mount to a place on the vehicle that has a good chassis ground. Usually on the swing-away tire racks it is necessary to run the coax down one of the support bars to allow it to be routed to the radio. In those cases, connect a 12ga or heavier black wire to the mount and run it down the support bar with the coax. Ground the end of the wire just inside the hatch or to the taillight bezel."

http://www.firestik.com/Tech_Docs/rack-mnt.htm

 

[Jerry Bransford]

This is directly from Firestik
"The ground problem should not discourage you from using one of these convenient mounting locations. All you need to do is to run a short (as short as possible) ground wire from the mount to a place on the vehicle that has a good chassis ground. Usually on the swing-away tire racks it is necessary to run the coax down one of the support bars to allow it to be routed to the radio. In those cases, connect a 12ga or heavier black wire to the mount and run it down the support bar with the coax. Ground the end of the wire just inside the hatch or to the taillight bezel."

http://www.firestik.com/Tech_Docs/rack-mnt.htm

I spent too many years in the industry to go along with all of Firestik's sometimes less than technically astute advice. I've found several blatantly incorrect statements on their website over the years and advising the use of a standard 12 guage wire for an RF ground is one of them. Not everything found on the the internet is true or correct.

Another of their real gems of incorrect information is that you need an 18' length of coax cable to get a low SWR. Totally false. Some antenna types are sensitive to feedline lengths, like no-ground plane antenna or with "balanced feedlines, but they're in the minority and not what we install onto our Jeeps. A little electronic/RF education makes that 18' length recommendation for a CB antenna sound right. Lots of electronic/RF education lets one understand why it's not true at all.

To understand a little of why standard wiring doesn't work well as an RF ground read up on the "skin effect" which talks about how RF tends to travel only on the surface of conductors. In fact in higher frequencies they use hollow square "waveguides" to transmit RF energy instead of cables or wiring. Because higher frequency RF doesn't travel through the center of wires they made them hollow. The large surface area of those and braided ground straps are what RF likes.

 

[reddvltj]

I spent too many years in the industry to go along with all of Firestik's sometimes less than technically astute advice. I've found several blatantly incorrect statements on their website over the years and advising the use of a standard 12 guage wire for an RF ground is one of them. Not everything found on the the internet is true or correct.

Another of their real gems of incorrect information is that you need an 18' length of coax cable to get a low SWR. Totally false. Some antenna types are sensitive to feedline lengths, like no-ground plane antenna or with "balanced feedlines, but they're in the minority and not what we install onto our Jeeps. A small amount of electronic/RF education makes that 18' length recommendation for a CB antenna sound right. Lots of electronic/RF education lets one understand why it's not true at all.

To understand a little of why standard wiring doesn't work well as6an RF ground read up on the "skin effect" which talks about how RF tends to travel only on the surface of conductors. In fact in higher frequencies they use hollow square "waveguides" to transmit RF energy instead of cables or wiring. Because higher frequency RF doesn't travel through the center of wires they made them hollow. The large surface area of those and braided ground straps are what RF likes.

Good to know Jerry, thank you! I know from many of the topics on here that buying into manufacturer claims for things like suspension related items without more in depth research is inviting trouble, I guess I shouldn't have assumed an antenna manufacturer wouldn't fall into that category too.

If the antenna is grounding to the mount itself, how is grounding to the mount via the body different from grounding to the mount through a shielded wire if the mount is powder coated, is where I was confused with the need for a braided ground strap.

 

[TurboTJ]

The longer the feed line, the better the VSWR will be at the radio due to the loss of the cable. Of course the loss that is making the VSWR better is also attenuating the signal. So if you want a perfect VSWR at the radio, use an infinitely long feed line. If you want to communicate with someone, use the shortest possible feed line and tune your antenna for best VSWR.

 

[connor grimes]

@Jerry Bransford about to install my cb antenna using the common tail light bracket, according to the diagram you provided if dremel down my bracket to bare metal on the underside, i will achieve a solid ground? will i also need to clean up any other spots? or is the underside of the bracket sufficient? thanks

 

[Jerry Bransford]

@Jerry Bransford about to install my cb antenna using the common tail light bracket, according to the diagram you provided if dremel down my bracket to bare metal on the underside, i will achieve a solid ground? will i also need to clean up any other spots? or is the underside of the bracket sufficient? thanks

There's a two-part answer.

The red arrows I added point out where where a ring of powder coating needs to be removed so the top of the SO-239 connector touches bare metal.

The bracket itself needs to have a solid ground connection to the tub too. What has worked for me was to add a larger diameter mounting bolt with a big washer under the bolt head and another under the nut to increase the contact surface area. Grind the powder coating away from around the new bolt hole on the bracket you'll need to add, large enough that the washer is touching bare metal. Then do the same inside the fender, scrape off an area big enough for the second washer so it touches bare metal too.

 

[connor grimes]

perfect thank you jerry

 

[Mr. Bills]

I use Teraflex tail light antenna brackets for both a 3/8" stud mount for CB and an NMO mount for ham.

Using a dremel tool I sanded a narrow ring around the bolt holes on both the antenna mount and tub to be sure there was a direct bare metal to bare metal connection between all three exterior mounting points and the tub. I also sanded a ring around the bolt hole for the "optional" third connection point on the interior of the tub.

I used the same dremel tool to get a good bare metal to bare metal connection on the underside of the Teraflex bracket where a standard Firestik stud mount connects to the Teraflex bracket, although I later switched to a stud mount that is insulated from the antenna bracket on both sides and uses ring terminals rather than a PL-259/SO-239 connection.

[In the photo below you can see where the ground for the coax attaches directly to the bracket and tub at that third "optional" mounting point where I sanded a ring around the bolt holes on the bracket on both the outside and inside of the tub.]

 

[gaabbee]

@Jerry Bransford. Where do you put your grounding strap? My guess is above the so-239 and below the mount? What about on the tub?

 

[Jerry Bransford]

Attaching the grounding strap to a bare spot on the tub is best but how you do it depends on where you will be mounting the bracket that the SO-239 is attached to And if the bracket is powder coated you must grind the powder coating away underneath where the nut and washer holding it in place so it can be grounded. The part of the mounting bracket that attaches to the tub (or wherever) must have its powder coating ground off where it touches to it can get a good bare metal connection too.

 

[gaabbee]

For anyone that looks at this and has the Teraflex tail light mount, so-239 and a Wilson 4' flex. Do not use the antenna grounding wire that comes on the Wilson. As soon as I removed it my SWR went from over 3 to 1.5. Also do a good job grinding the powder coat off the mount and use the extra bolt hole that is provided.

 

[Jerry Bransford]

X2, that little short grounding wire usually just raises the SWR when it is grounded. Best to just cut it off in typical antenna installations.