extremely high SWR and won't work

[dnovember99]

So I have installed my CB radio. I have the antenna mounted on the truck bed via a bracket. Routed the coax cable under the truck and along the chassis, into the truck and to the CB. I have a cobra 75 WX ST and 4' fire stick antenna.

When I started to test the SWR, I was seeing that the levels were at a 6! After reading stuff for a few days I thought it was a grounding issue so I took the bracket off and sanded the paint off the back so it would connect good to the truck bed. Reading is still the same.

So now I am trying to figure out if the issue is a bum radio (a friend gave me his old one when he upgraded), bad coax cable or a bad antenna.

Anyone have any thoughts? Thanks for the help

 

[WA0CBW]

I would start with the coax connector, the coax, the antenna.
bb

 

[dnovember99]

I would start with the coax connector, the coax, the antenna.
bb

Is there a way to test the coax cable to see if is bad? I was going to pull it out if there is a way to do so

 

[mmckenna]

So now I am trying to figure out if the issue is a bum radio (a friend gave me his old one when he upgraded), bad coax cable or a bad antenna.

Anyone have any thoughts? Thanks for the help

… or bad SWR meter. Or incorrectly hooked up, adjusted, etc.

Couple of places to look:
CB needs to have clean power off the battery.
CB chassis should be grounded.
You need to have appropriate coaxial cable with properly installed connectors. Connectors are usually where these sorts of issues arise.
Antenna needs to be properly mounted.
Most antennas require a ground plane underneath them to work properly. Ground planes and RF grounds are different than DC electrical grounds. Edge of the truck bed is less than ideal, but it'll work. Sanding the paint off and making sure it's grounded is a good start.

Other place there is often an issue is at the antenna mount. Not sure what kind you have, but for the 3/8x24 threaded mounts, you need to make sure your mount is installed correctly. There's usually some insulating washers that separate the threaded part where the antenna screws in from the mounting bracket. If those are missing or installed incorrectly, it'll give you a dead short to ground, and a high SWR reading.

If you are good with a multimeter, disconnect the coaxial cable at the radio end ONLY. Leave it hooked up at the antenna.
Using the continuity test function on the meter, check for a short between the center pin of the connector and the outer shield at the radio end of the coax. If there is a short, stop and fix. It should not be shorted.
If that checks out...
Check for continuity between the center conductor on the radio end of the coax to the threaded part where the antenna connects. That should show a solid connection.
Also, check from the outer shield at the radio end of the coax to the antenna mount where it attaches to the truck body. Should show a good connection.

If all those check out, then suspect your antenna.

 

[522]

...... you need to make sure your mount is installed correctly. There's usually some insulating washers that separate the threaded part where the antenna screws in from the mounting bracket. If those are missing or installed incorrectly, it'll give you a dead short to ground, and a high SWR reading.

This is the first thing that popped in my head. Double check where that plastic washer is placed.

 

[dnovember99]

I would start with the coax connector, the coax, the antenna.
bb

Is there a way to test the coax cable to see if is bad? I was going to pull it out if there is a way to do so

… or bad SWR meter. Or incorrectly hooked up, adjusted, etc.

Couple of places to look:
CB needs to have clean power off the battery.
CB chassis should be grounded.
You need to have appropriate coaxial cable with properly installed connectors. Connectors are usually where these sorts of issues arise.
Antenna needs to be properly mounted.
Most antennas require a ground plane underneath them to work properly. Ground planes and RF grounds are different than DC electrical grounds. Edge of the truck bed is less than ideal, but it'll work. Sanding the paint off and making sure it's grounded is a good start.

Other place there is often an issue is at the antenna mount. Not sure what kind you have, but for the 3/8x24 threaded mounts, you need to make sure your mount is installed correctly. There's usually some insulating washers that separate the threaded part where the antenna screws in from the mounting bracket. If those are missing or installed incorrectly, it'll give you a dead short to ground, and a high SWR reading.

If you are good with a multimeter, disconnect the coaxial cable at the radio end ONLY. Leave it hooked up at the antenna.
Using the continuity test function on the meter, check for a short between the center pin of the connector and the outer shield at the radio end of the coax. If there is a short, stop and fix. It should not be shorted.
If that checks out...
Check for continuity between the center conductor on the radio end of the coax to the threaded part where the antenna connects. That should show a solid connection.
Also, check from the outer shield at the radio end of the coax to the antenna mount where it attaches to the truck body. Should show a good connection.

If all those check out, then suspect your antenna.

Wow! A ton of good information! Thank you.

So I just pulled the coax cable out. I figured this was gonna be a good start. Also I don't think I had the best routing or one that I wanted to have lol.

So with my multimeter I did a center pin to center pin, that was a good reading. Shield to shield and that was good also. Then picked one end and did center pin to shield and that was also a good reading. So the coax seems to be good.

I am almost wondering if I should buy a new set of mounting rings (the plastic washer, flat washer and lock washer) before I go out for a new antenna?

As for the antenna mount I got it here 2005-2015 2nd Gen Toyota Tacoma CB Antenna Mount - Stainless Steel

Sorry it won't let me add the link the proper way so my apologies
Thank you

 

[prcguy]

Yup, insulating washer in the wrong spot is a very common problem. If that's not it then check continuity with an ohmeter as mentioned before. One thing I would avoid is replacing connectors or doing anything radical until you actually know what the problem is. Too many times people will start changing things that have nothing to do with the problem, wasting lots of time and parts. See if you can find someone local with an antenna analyzer, that will tell you lots of stuff and rule out a potential bad SWR meter in the radio.

This is the first thing that popped in my head. Double check where that plastic washer is placed.

 

[dnovember99]

This is the first thing that popped in my head. Double check where that plastic washer is placed.

This is how I have it set up.

 

[mmckenna]

I am almost wondering if I should buy a new set of mounting rings (the plastic washer, flat washer and lock washer) before I go out for a new antenna?

No, not yet.
Reconnect your coaxial cable to the antenna mount. Leave the antenna off.
With your multimeter at the radio end of the coaxial cable, check for a short between the center pin and the outer shield. Since you already proved the cable is good, that will tell you if the issue is at the mount. It should show as an open. If it does, then check between the center pin of the coax and a known good ground point inside the cab. It should still show as an open.

Now, install the antenna, repeat the test, it should still show as open.

If your test leads are long enough (maybe use an extra length of wire) check from the center pin of the coax at the radio end to the point where the antenna threads on the mount. There should be a good low resistance connection there.

If it fails any of those tests, stop and fix.

If it all checks out, then you need to start looking at the antenna —AND— your SWR meter. If the SWR keeps reading high, try a different SWR if you can get hold of one. Also, make 100% sure it is hooked up and you are using it correctly. I'm sure you've already double checked, but ruling out faulty test equipment should be one of the steps.

 

[dnovember99]

No, not yet.
Reconnect your coaxial cable to the antenna mount. Leave the antenna off.
With your multimeter at the radio end of the coaxial cable, check for a short between the center pin and the outer shield. Since you already proved the cable is good, that will tell you if the issue is at the mount. It should show as an open. If it does, then check between the center pin of the coax and a known good ground point inside the cab. It should still show as an open.

Now, install the antenna, repeat the test, it should still show as open.

If your test leads are long enough (maybe use an extra length of wire) check from the center pin of the coax at the radio end to the point where the antenna threads on the mount. There should be a good low resistance connection there.

If it fails any of those tests, stop and fix.

If it all checks out, then you need to start looking at the antenna —AND— your SWR meter. If the SWR keeps reading high, try a different SWR if you can get hold of one. Also, make 100% sure it is hooked up and you are using it correctly. I'm sure you've already double checked, but ruling out faulty test equipment should be one of the steps.

Perfect! Thank you for this help. I will do this later this afternoon. I will post my findings to try and eliminate the course of the issues

 

[mmckenna]

Perfect! Thank you for this help. I will do this later this afternoon. I will post my findings to try and eliminate the course of the issues

OK. There's not a lot that can go wrong. About the only other issues you could have after this:
SWR meter is bad.
Antenna is bad. The fiberglass whips can sometimes crack and damage the radiating element.

One thing at a time until you find the issue. You've already ruled out the coax, so you're down to only a few other components.


I like that mount, looks like a good design. One thing I'd make sure of is that the bracket is making really good contact with the body. I know you said you sanded it down so it's bare metal, but over time that might rust/corrode. Keep an eye on it. Maybe add some "No-Ox-Id" under it to keep it sealed and making a good connection.

 

[dnovember99]

No, not yet.
Reconnect your coaxial cable to the antenna mount. Leave the antenna off.
With your multimeter at the radio end of the coaxial cable, check for a short between the center pin and the outer shield. Since you already proved the cable is good, that will tell you if the issue is at the mount. It should show as an open. If it does, then check between the center pin of the coax and a known good ground point inside the cab. It should still show as an open.

Now, install the antenna, repeat the test, it should still show as open.

If your test leads are long enough (maybe use an extra length of wire) check from the center pin of the coax at the radio end to the point where the antenna threads on the mount. There should be a good low resistance connection there.

If it fails any of those tests, stop and fix.

If it all checks out, then you need to start looking at the antenna —AND— your SWR meter. If the SWR keeps reading high, try a different SWR if you can get hold of one. Also, make 100% sure it is hooked up and you are using it correctly. I'm sure you've already double checked, but ruling out faulty test equipment should be one of the steps.

Perfect! Thank you for this help. I will do this later this afternoon. I will post my findings to try and eliminate the cause of the issues

 

[dnovember99]

OK. There's not a lot that can go wrong. About the only other issues you could have after this:
SWR meter is bad.
Antenna is bad. The fiberglass whips can sometimes crack and damage the radiating element.

One thing at a time until you find the issue. You've already ruled out the coax, so you're down to only a few other components.


I like that mount, looks like a good design. One thing I'd make sure of is that the bracket is making really good contact with the body. I know you said you sanded it down so it's bare metal, but over time that might rust/corrode. Keep an eye on it. Maybe add some "No-Ox-Id" under it to keep it sealed and making a good connection.

Ok so I hooked one end of the cable to the mount, and did a reading from the center pin to the mount and no beep on the meter, but when I touch the bolt that is holding it in the meter beeps.

Does this mean there is a grounding issue?

 

[Chronic]

if i understand that correctly that means the center pin is shorted to ground and that is not good.

 

[dnovember99]

if i understand that correctly that means the center pin is shorted to ground and that is not good.

Ok so I am not sure if this will help explain it better or not. I guess I am just not sure I know I am explaining it correctly.

 

[mmckenna]

OK, you've got a dead short in your mount. That means that likely one or both of the insulating washers are installed incorrectly.

If you take the antenna mount off the bracket, you should be able to see how it goes together to keep the two isolated.

That would certainly give you high SWR.

 

[mmckenna]

In the second photo, it's not beeping since the coating on the bracket is acting as an insulator. When you touch to the bolt, that's not insulated by any coatings, so it's showing a short circuit. Easy fix, if you have all the parts.

 

[dnovember99]

In the second photo, it's not beeping since the coating on the bracket is acting as an insulator. When you touch to the bolt, that's not insulated by any coatings, so it's showing a short circuit. Easy fix, if you have all the parts.

Ok, so if I understand this all correctly, I need to have two isolation rings? One on each side? When this was all given to me, I only got one isolation ring.

 

[mmckenna]

Ok, so if I understand this all correctly, I need to have two isolation rings? One on each side? When this was all given to me, I only got one isolation ring.

Yep, there's your problem right there.

The part where the antenna screws in needs to be isolated from the mounting bracket. If not, you have a dead short to ground and it will never work.

 

[prcguy]

There should only be one plastic shoulder washer with that type mount. It uses an SO-239 socket that grounds to the metal on the under side of the mount, then an insulated 3/8" stud sticks through the hole in the mount with a plastic shoulder washer against the mount on the top side, then a flat washer, then a lock washer, then the double female threaded thing. The picture in post #8 looks correct.

Ok, so if I understand this all correctly, I need to have two isolation rings? One on each side? When this was all given to me, I only got one isolation ring.