Sure one more high SWR

[R290]

Ok my setup. GE Mobile CB model 3-5809D 10 years old but in like new condition.
Antenna wire RG58 50 ohm 18'. Antenna length 2' fiber glass stick mounted in the center of my metal roof on my truck, it has a spring foldover mount.

My SRW are running 6-7 :headbang

Everything I have read says my ground plane must be messed up. The roof to is bolted to the body in like 12 places so it's grounded to the body and the body is grounded to the battery.

Here is what I'm thinking, trying a different antenna, just to see if it goes up or down. SWR are about the same CH 1 vs Ch 40 too.

I will post a pic soon so you can see what it looks like just so you can point out the obvious:blush:

 

[Robb]

Sounds like your antenna is just too short!
What do you expect to get out a 2 ft antenna anyway?
Put a REAL antenna on it.

Did you check the coax with an ohmeter for a short?
What did you test besides the SWR?
Do you need all of the 18 ft; or is it bundled up or cut to fit the application?
Does the coax have any defects along its length?
Smashed; flattened?

EDIT: Don't talk on it until your SWR problem is solved, OR - you will BURN UP the OUTPUT FINAL TRANSISTORS in the radio!!!
Then; it won't talk out anymore...

 

[R290]

LOL. We just use the CB to talk on the 4x4 trails, so its mosly just a few hundred feet apart. I did not test the coax for a short. I will check that right away, I will be home in 2 hours and can measure that.
I guess I don't know what to to test, is the problem. I did check the top was grounded to the body but thats about it. The cable could be shorten, but it just winds around the cab a bit., no smashed or flat spots.

Edit Storm Lake IA?? small world my cousin lives there.

 

[W5LZ]

Sounds like your 'ground' is probably just fine. Also sounds like you haven't tried tuning, or adjusting, the antenna, which is also required, none of them are 'plug-n-play'.
Like most things, if you know how to do that adjusting/tuning, it isn't difficult. If you don't, then it can certainly be confusing. So if you are not too familiar with all this stuff, I would suggest that you find someone who is so they can do it for you. (Pay attention so you can do it next time!)

Just a few observations that might be helpful.
Short antennas can be 'pickier' than longer antennas about adjusting correctly. That's because they are typically less than optimal to start with. Even after doing that adjustment, they are limited in ability, so don't expect much from them.

The feed line, that cable going between radio and antenna has one specific purpose, just like a water hose. It's supposed to get the signal from the radio to the antenna and that's it. It can be used for another purpose though, and that's to fool the radio into thinking it's seeing a properly adjusted antenna. That's done quite often. It is never the 'best' thing to do, but sometimes it's all that can be done under certain circumstances. That's why you see certain "magic" lengths used with antennas sometimes. If the length you happen to have is too long, cutting it off is not a bad thing. Or, just get it out of the way some way. Either will work.

And lastly, there's nothing "magic" about any of this stuff. It isn't always understood so it may seem 'magic', but it isn't. There are some very good reasons for doing things a certain way, and then there are a lot of misunderstandings/myths about it. Knowing which is which can be a lot of fun sometimes. Don't believe everything you read!
Good luck and have fun.
- 'Doc

 

[R290]

Ok double checked the frame to body to top and it's basically zero ohm's. Tried a 4' antenna no difference.

Then check to the washer on the roof and it was high resistance. So I took it all apart and notice that the insulator keeps the base of the antenna from touching the roof. I looked on-line and maybe I have the wrong roof connector.

mine is like this, sort of.

then I found this one

Pic of mine are attached.

 

[mackmobile43]

Ok double checked the frame to body to top and it's basically zero ohm's. Tried a 4' antenna no difference.

Then check to the washer on the roof and it was high resistance. So I took it all apart and notice that the insulator keeps the base of the antenna from touching the roof. I looked on-line and maybe I have the wrong roof connector.

mine is like this, sort of.

then I found this one

Pic of mine are attached.

In this picture your insulating shoulder washer (the white plastic thing) should be under the antenna.

The insulator washer does what it's called and that's to insulate the antenna from ground, the way it's pictured below allows the antenna a path directly to ground.

To assemble this correctly put the so-239 connector through the mount then slide the insulator over the threaded portion of the so-239 with the shoulder side of the insulating washer facing down and then screw on the antenna and that will give you a correct mounting assembly and most likely cure your infinite swr reading.

It should look like this one.

 

[W5LZ]

I'm not sure I'm see things correctly so tell me if it's like this.
The insulator 'B' goes into the hole in the metal roof from the top side. Only the small ring of the insulator 'D' extends through the roof. The inside part of the connector 'A' goes through the insulator in the hole and screws into 'C'. 'C' is insulated from the metal roof by the large part of the insulator, so no contact between roof and top part of the antenna mount, infinite resistance. The inside part of the mount that the coax screws onto DOES make contact with the metal roof, zero resistance between the two. The inner pin of that bottom part should have electrical contact with the top part of the antenna mount and the antenna, but no contact to the metal roof.
I can't be sure of those washers. One on the inside of the roof would be fine, just insures metal to metal contact with the 'inside' portion of the mount. But, unless that top washer is insulated on the roof side of it, it could defeat the purpose of the insulator. If it's insulated so that it does NOT make electrical contact with the roof, then it should work fine. I'n not sure I said that so it can be understood. Was it?
- 'Doc

Can't figure out how to attach a picture, so.
'A' refers to the inside portion of the mount that has the threaded end which the coax screws onto.
'B' refers to the insulator.
'C' refers to the top/outer portion of the mount.
'D' refers to the small 'ring' of the insulator that fits in the hole through the roof.


Sorry 'mackmobile43', the large blue tinted picture of the assembled mount has the insulator exactly backwards. The large 'flange' of that insulator is to keep the top part of the mount from contacting the metal roof. A large washer on the outside of the mounting hole defeats the insulator's purpose, keeping the antenna from grounding out on the roof. Some type of insulated 'washer' on the top of the roof would certainly work though, or an insulated 'gasket' between that washer and the roof. A large washer inside is fine, just makes more metal to metal contact between the roof and the 'ground' portion of the mount.
This has gotten more 'wordy' than I want, but don't know how else to say it, sorry.

 

[R290]

Thanks guys, I blew it when I added the washers. I put it on without the washers and the SWR is a lot better. Now I can tune it from here.

Those fiberglass antenna are heavy and might bend the roof sheet metal. Will look around for something lighter.

 

[Robb]

At least get a mag-mount K-40. That will work OK, it's pretty flexible on the top. Get a rubber plug for the hole - then put your antenna wire thru that plug after making a hole big enough for the coax end to go thru. Then, seal it up with some silicone caulk.

Thinking out loud...

 

[hotrod]

if ya just using it fior trails and ya not worried about distance just buy either
a k30 or lil willie wilson these are only 3ft but for thier lenth they work decent
and have good swrs.mount them on your roof

 

[R290]

I looked at the Wilson 1000, not sure it that antenna can handle the 4-5 watts I'm pumping out
My issue with antenna's is height of my carport. I'm thinking of moving the antenna from the roof to the cowl, or fender, as that would bend/fit under it better. The Wilson 1000 looks do able.