CB Antennas and mount points

[Kejtar]

Well, I kind of need to mount a new antenna on my XJ to replace one I ripped off on a friendly rock/tree stump (not really sure which one finally took it off my jeep).
In any case, what I'm looking to do is 2 antenna setup: One front and one in the rear. I know radio shack sells a 2 antenna setup with 2 short fiberglass whips, but here's what I'm thinking:

Short 2 foot whip on the front bumper and my long metal whip on the rear bumper. There are only two things I don't remember (I got someplace antenna book and theory, but I can't find the damn thing):
1. what are the repercussions of two mismatched antennas? Would the waves interfere with each other? cancel each other out? amplify each other? or would it depend on the dispersal pattern of each antenna?

2. that cable that they use in the 2 antenna setups: is it just plain T or is it something special?

 

[8Mud]

I´m not a radio engineer, but owning a good SWR meter and playing with it since 1964. I´ve learned that any way you can reduce the variables the better and more consistant the SWR.
It changes when you park next to a building, it really changes when you park next to a chain link fence, it changes when the doors are open, somebody is walking past or whatever.
A second antenna is just another variable to mess with and would probably end up being pretty directional.
A good rule of thumb, is to try and mount it as close to center of mass as practical and on a flat metal surface (the roof) and make sure you sand to bare metal (have a good ground). Antennas are another, can of worms, some work well, some don´t, price is often not the deciding factor on how well they will work. What works on one guys Jeep and his radio isn´t necessarily gonna to work well on yours.
I´ve broken off dozens of fiber glass whips, haven´t broken of an antenna since 1988 and after switching to a K-40 and a six inch washer under the sheet metal on the roof (though I have bent the sheet metal roof a bit and had to straighten the antenna a few times).

 

[sportsguy]

The second folder in the list has my CB & antenna set up:

http://community.webshots.com/user/sports_guy

I've had it tuned and I'm at under 1 on the SWR on ALL channels (I really have no life...LOL). Some are slightly higher than others, but under 1 across the board - I'm happy.

The antenna bracket is folded steel and mounts to the fender via an existing fender bolt. Heavy Duty cable ensures no worries with the ends (soldered).

I had a mag-mount for the roof and gave up on that.

The current antenna is a 3' K-40 - it's great; highly recommended. The only difference between those pics and today's set up is the addition of a quick-disco for the antenna. I sometimes need to park down-town in garages, so rather than bang my K-40 off crap, I simply remove it.

One of the guys in my club runs a dual 3' set-up on top of his roof-rack - really, really tall, but no better or worse than mine RX/TX wise. Don't know his SWR numbers, but he did get them tuned (they came as a kit). I just don't care for that much antenna - I'll throw my money into a decent CB - that's where most folks notice the biggest difference after tuning their antennas.

One of the TJ guys in our club is running a fully tuned whip - and he can't hear me when I'm in line behind him...his radio is a POS. He tried another brand one day to see what was up - night & day...

 

[Jeff 98XJ WI]

It is my understanding that the truckers that have the dual antennas do this because it makes the field an oblong lobe long to the front and back of the rig. This concentrates their signals in front of and behind them on the highway and not off to the side where there aren't many other trucks. An omni-directional pattern is better for fourwheelers since they are NEVER traveling is a long straight line. You'll get the best omni pattern with a single antenna in the center of the roof. I used a Larson semi professional type whip/coil NMO 27B with an NMO mount. The mount uses a 3/4" hole and o-rings to seal everything up. I also purchased a cap for the mount for when I don't want the antenna up there. Jeff

 

[sintax]

Sportsguy: If I buy you a plane ticket will you please come tune my setup? :badpc:

I'm almost done playing with it, I just cant get it right. :smsoap:

-Scott

 

[xjrugger]

There must be something wrong with his medulla oblangotta. I seem to have troubles with my cb not picking up signals on the highway, but when i get on the trail it's fine. Could it be that i have it mounted to a tube rear bumper with the radio shack metal whip (the bumper being the issue i think)? Plus the radio was bought by an ex girlfriend years and years ago so i think the radio could be short of great. I pick up a lot of interference or it will give nothing on the highway, but on the trail i make good contact.

 

[PhatXJ]

I built my own bracket and mounted it up near the radio antenna. The antenna is an adjustable 3' Valor Halfbreed stainless whip. My radio is a $40 RadioShack mini digital.

I have no idea what my SWR is but I get an excellent, clean and clear signal either on the highway or on the trail.

 

[ladywolf]

i cant say much about cbs, but all i ask is that you mount the antennae somewheres where it isnt gonna smack someone if ya bounce of something. i've been on the receiving end of a madly flailing 15 ft whip and it left a pretty good welt.

 

[PhatXJ]

15 foot whip?!?!?!

 

[RichP]

15 foot whip?!?!?!

Yea, they come that big, we had big two piece fiberglass ones on military vehicles on spring loaded bases and they have been known to break collar bones and fracture skulls. I had one break my hummers windshield when the driver that was parked angled away from me released his from the hold down, plastic tip broke off and 8 inches of antenna itself came thru and nicked the steering wheel...

The two antennas that truckers use are to eliminate the dead spot that fans out from behind the triailer. Best setup is either a hole thru the roof with a permanent mount or a good mag mount. For a few years I had a gutter mount that would fold down along the gutter, that thing worked great. Been looking for another one on and off but have not found one since radio shack stopped selling them.
There is also a z shaped mount that goes between the hood and fender on the drivers side. it will take a standard antenna and I have even seen one that will fold down across the top of the motor after you open the hood almost straight up [you do know that jeep hoods open pretty far right ?] then close the hood and its out of sight, downside is you are limited to about 38 inches or so. It ends up about even with the factory am/fm antenna.
Me, I just use a mag mount on the roof, when not in use I take my maxtor all in the mike radio an the antenna out and put it in the cellar or move it to another of our jeeps if the kids are going out to play

 

[ladywolf]

Rich, dont even get me started on military whips (you ever shock a newbie out playin w/ an antennae? (major evil grin) i'm talking about the old style ones that almost look like the skinny ones you'd put a marker flag on top for people on ATV's....i've gotten nailed w/ that before. i've gotten bopped w/ the plastic end of a military one cuz one of the guys was messin around w/ it....he pulled it back and let it go, and i happened to be walkin by....i was NOT happy!

Kris

 

[Kejtar]

i cant say much about cbs, but all i ask is that you mount the antennae somewheres where it isnt gonna smack someone if ya bounce of something. i've been on the receiving end of a madly flailing 15 ft whip and it left a pretty good welt.

I know what you mean and that's why my tall steel whip was always strapped to the XJ to prevent it from flapping around.

 

[greentowtruck]

The best place to mount an antenna on just about any rig is right in the middle of the roof with just a single whip. that gives you the best multi directional capability. dual antennas should be mounted straight across from each other but tend to be directional to the front and rear of the vehicle unless you can get them 8 feet apart although the middle of the roof is hard when you run a roof rack or anything else on top pf your jeep. I am currently in the design and buid stages of my 90 xj but i am probably going to put an antenna mount on my roof rack to mount a wilson 5000 roof mount antenna

on another note if an antenna is mounted on the front right of a vehicle its best reception and transmitt power will radiate towards the left rear if mounted to the left front it will radiate to the right rear and so on

 

[sjx40250]

108" whip is the longest I have known about. I beileve it is a full 1/4 wave length for CB's and is the optimum tuned length. Shorter antenna are usually "loaded" some with a coil to emulate the 108" performance. Have to be careful when I say this but, the best performance is straight up. Clipping it to the gutter, etc. acutually degrades performance.