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I need to see some pics of your CB?

Grounding through the coax, does not work, quick way to burn up a radio.

Not sure, i don't remember if the mounting screws for the mirror are contacting metal, or if they were isolated or mounting a plastic type mount.
 
Not sure where the misunderstanding is here but I have always seen the rigid mount antennas use a plastic gromment(sp) to isolate the antenna from the mount and the vehicle.
The radio will be grounded with the power wires.
 
The antenna is not grounded to the chassis, like Tom said there is an isolator in the antenna mount. Also the CB itself should have a seperate ground to the chassis of the CB and DO NOT rely on the negative battery connection as a ground, the instructions that come with a CB tell you to run a seperate ground to the little ground screw on the back of the unit.
 
I just finnished it, and it works. I looked and there is no additional ground screw on the back of the unit. Cobra 29LTD. The instructions stated red to battery, I used fuse block, and neg to chassis. That's what I did. The antenna mount does have a plastic grommet between the mount and atenna. It looks clean and works. I tuned the antenna and talked to someone and he said I sounded clear. Sweet!!! Thanks guys for all the help!!
 
ok, guess there was a missunderstanding then, yes there is a plastic piece between the actual antenna whip, and the ground mounting unit, what i thought you were referring to, was there is no need for it to be grounded, but yes, as soon as the mount is attatched to the body, or something attatched to the body, somehow, and has a direct ground path to the metal, it's fine.

sorry for any confusion :whistle: :doah::D
 
One of these days, if someone asks, or if I get bored, I may write up a small piece on Ohms Law and how voltage drop works.

But, I AM NOT going to write up a piece on antenna theory.

It would take volumes, and cause the biggest flame war you ever saw. Even though I could give references and documents proving every thing I said.

Having said that, let me clear up a couple of issues.

The antenna, the part that is hooked to the center conductor of the coax MUST NOT be touching or hooked to ground.
Good way to possibly burn up a final.

But, unless it is a special marine-type antenna designed to be mounted on fiberglass, it MUST be mounted to metal that is grounded to the same ground reference that the transmitter is grounded to.
This piece of metal is what the little connector on the end of the braid is hooked to at the antenna.
Now, since the braid is grounded at the radio end, it will electrically ground the metal that it is hooked to at the mount.
And this will work, after a fashion.
But among other things, it tends to cause an RF current in the braid, and that is normally not a good thing.

The thing is, the antenna you put up and looks so pretty there, is only half the antenna.
The ground plane, the metal under it that it is mounted on, is the other half.
And the amount of it, and its shape, helps determine the radiation pattern.

IN GENERAL, the antenna transmits and receives best in the direction of the most metal.
In other words, if you have a metal top, and you mounted a whip on the left rear of the top, then the signal would be strongest towards the right front.
Mounting it on the left rear bumper, would seem to do the same thing, but having it run right past the metal body and top makes for some strange differences.

You get all kinds of weird reflective wave problems coming back to the radio, and there is sometimes some "backscatter" off the metal roof and body that causes a small lobe of RF energy in the opposite direction.
But, just in general you just lose power as its absorbed by the metal and by warming up the coax slightly.

In one of those cases, I usually recommend a top loaded antenna. Firestick makes them I think.

http://www.firestik.com/CatalogFrame.htm

There are lots of others.
If you go with Firestick, I suggest the Firestick II series.
It has a tunable tip where you adjust your antenna with a screw in the tip of it.
Some of the others have those too.
Usually they are worth it.

The top loaded antenna transmits most of it signal from the top. Look at one, and you will see the larger coil at the top.
Electrically, this is where most of the antenna is, so that is where most of the signal goes out.
If you have one of these mounted on the back bumper, and its tall enough to get that coil above the roof, it will work better.
 
Damm Fordum, that was pretty good right there. You lost me a couple times. When on my last wheelin trip, out of 16 rigs, I was the only one without one. Theyy were on them quite often. I need ed it a few times. People would stop, get out and come over to tell me what was going on. So, for the most part, it will be used on the trail with other rigs close to me. I also wanted this for camping and in the backwoods if in case I needed help or something.

The antenna I got was from the local Freightliner dealership. It is an Alliance 48" fiberglass antenna. It has a "Freightliner" logo in a couple spots. It says if tuning is necessary to trim the top 1/8" at a time. I didn't need to, so far. It also says its a CB/WB antenna. I don't know what WB stands for though. It is 2.5ft above the roof line. This should work for what I need it for, but if I could make it better, I would.

Thanks for the info!!!
 
Yep, WB is weather band.
A lot of the CBs have the national weather band built into them now, and so some of the antennas have a wb designation.

If I had to guess, and I would because I have not done any research into it, I would say that most likely there is no difference between an antenna marked WB and one that is not.
Most probably a marketing idea.

ALL mobile antennas mounting setups are compromises.
The best thing to keep in mind, is the higher the better, the less metal above the mount the better, and the more metal and the more even distance around under the mount the better.

If you had a 102/108 inch whip mounted in the center of a round piece of steel about 36 feet across, you would have very close to an ideal setup.
This would give you a nice even pattern all the way around.

Of course, you would have zero "gain". If you want "gain", you have to give up something.
FWIW, antennas do not increase power. There is no actual gain.

What is called gain, is just taking the power from a direction you don't need and adding it to the direction you want.

But, we are starting to get into the deep water of antenna theory.
I don't mind answering questions, so fire away, just don't be upset if I don't come back with a really detailed answer.
Because sometimes the details get really detailed<G>.

Also, absolute answers are few and far between. I have seen antenna setups that could not work under any circumstances, but do.

Munepit, your setup sounds ok.
But, if you start realizing that you can hear a lot farther than you can talk, or you start hearing your transmitting in the am/fm radio, or the filings in your teeth, try a ground strap from a good ground to the door and then to the mirror mount.

Actually, if you start hearing it in the filings of your teeth, do the grounding, but check your SWRs and consider turning off that amp.........:D.

BTW, I mentioned this in another post, but if anyone has small kids, you have to do this.
Try it first to make sure it works, but grab a fluorescent light bulb.
The bigger the better. It does not have to be a good bulb as long as its intact.
Have someone key the mic and hold it down while you hold the bulb by the glass at one end and touch it to the antenna.

The whole bulb should light up. Depending on how much power you are getting out, you should be able to move it away a short distance after you fire it.
Looks cool, and really impresses the little ones.
Of course, it needs to be at night..
 
Fordum said:
Have someone key the mic and hold it down while you hold the bulb by the glass at one end and touch it to the antenna.

The whole bulb should light up. Depending on how much power you are getting out, you should be able to move it away a short distance after you fire it.
Looks cool, and really impresses the little ones.
Of course, it needs to be at night..
Click to expand...


I'm trying this when I put my antenna back on. :D
 
When a friend of mine and I used to do a lot of night runs around town while holding discussions on the CB, we each had a little NE2 neon bulb from Radio Shak
hooked on the top of our steel whips by its lead wires.

When one of us was talking, the little bulb would light up orange.
If the other needed to say something real quick, he would key his mic and the flash would let the other guy know to unkey.

I left it on there when I went to college.
One night, I was making a night run from Coco Beach back to Orlando, and got in a conversation with another guy making the same run.
Since he was behind me, I ran his front door so he could catch up.

When he came up behind, he commented on my little flashy bulb. I thanked him as he was passing me.
He got by me, keyed his mic, and asked how I liked his.
The whole back end of his car lit up!

He had taped a small F5 six or 8 inch flouresent bulb to his short fiberglass whip which was on a truck mount.
It was taped top and bottom lengthwise along the top of the whip, on the back side.

Wasn't real practical, he said he went through one every couple of weeks.
Sometimes it was a limb or something, but sometimes he suspected just a really big bug.

Of course, I tried it on mine, but my small base loaded steel whip was just not stiff enough to hold it up at speed.
 
You may not need it, but when I mounted my antenna on the mirror of Krusty, I had to run a wire from the mount to metal to get a good ground. Nothing I did before doing this would allow me to tune the antenna and get a low enough SWR. As soon as I ran this wire to a solid chassis ground I was able to lock in the SWR at slightly less than what was needed and got good clean signal. It might have just been the rust on Krusty though.
 
I used to tape those small camping lantern fluorescent bulbs to the tops of my fiberglass CB antennas when i drove truck cross country, they really only lit up when i had the heater turned on to a minimum of about 75 watts, and even then it was real dim, when i cranked it up to 250 they would really glow.

Then i heard one day that doing this light bulb show, really messes with the SWR, didn't have any proof of it, but i took them off anyways, and besides, sometimes i didn't want anybody knowing it was me talking :whistle: :D
 
Here are a few pics of the install. Thnks guys for all the input. Im going to try out that lightbulb trick!

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