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Mounting CB/ FM antennas on light bar? Better reception?

Plays For Jeeps

NAXJA Forum User
Location
Allentown PA
I have a FM modulator which combines my CB and Radio antennas into one single mast.

Reception sucks.

I was wondering if I could expect any better reception switching to a lightbar mounted antenna. This isn't a tiny flimsy light bar either, its a 2in square tubing ex- ladder rack from the Junkyard that I took 7 inches out of, grinded, cut, and undercoated. Its beefy.

How about a steel 101" whip antenna?

Thanks guys!
 
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from my CB research on various sites dual purpose antennas lick donkey nuts. I would run a second antenna for your CB. 102" would probably yeild the best reception but if that is mounted on top of your jeep on a light bar... thats going to be close for a power line smacker.... I'd hate to see you try and pull some back to the future shit at 88mph :looser:
 
^Agreed, the dual purpose came on the XJ when I got it.

I was thinking about the 102" on the rack running the dual purpose and plugging the hole on the pass. fender.

But I guess Ill just run two antennas. Stock for the radio and a steel whip off the rear bumper for the CB.
 
Run two antennae. You're better off using a quarter-wave or a half-wave on any radio, rather than using a 'multiband' whip. (Either a quarter of the wavelength/band you're operating on, or half of the length.)

Also, rather than putting them on the roof rack, put them directly on the roof. The roofline would provide a ground plane that will actually increase the efficiency of your antenna slightly (but measurably) - unless you're going to stick it in the middle of the roof rack.
 
^I was going to stick it on the actual light bar. Do you think I would better off mounting on the actual roof though? Would you reconmend running both antennas onto the roof, radio and CB for branch reasons?

Thanks
 
You can leave the BFM antenna where it is on the fender - it's just receiving signals, and shouldn't have any trouble there.

The CB antenna would be better mounted directly on the roof, since you are transmitting through it at times. The ground plane helps with transmission stability, and keeps RF away from you (using the roofline for a ground will help that rather more than just having the roofline between you and the antenna - use a PL/SO-250 socket and plug assembly for that. As I recall, it works well in the CB band, you can get them weathertight, and that will ground the socket to the roof plane.)

Using a PL-259 and SO-259 will allow you to remove the antenna for whatever reason, should you need to (garages, carwashes, ...) and, as I recall, you can find a "weather cap" for the SO-259 for when you have the antenna off (put it in the glove box on centre console when you have the antenna mounted.) A quarter-wave CB whip would probably fit neatly down the side somewhere when you're not using it.

Now you've got me thinking...
 
^ That would explain the Nylon plug in my roof near the rear I found today.

Would it be best mounted in the middle of the roof or the rear? I guess I would have to cut a hole in the headliner huh?

And when you say quarter whip, do you mean a 4 foot steel whip? I currently have a 4foot Firestik in the fender.
 
Ideally, you put the antenna in the centre of the ground plane - but it's not totally necessary. You don't need to cut a hole in the headliner tho - just pull the board, run your cable and mount the socket, and reinstall the board. The cable can go up behind trim somewhere convenient (Usually the A-pillar, but the B-pillar may have more room behind it.)

CB is, as I recall, the "eleven metre" band. So;

11 x 39.4 (convert to inches) = 433.4"
433.4 / 4 (get quarter-wavelength) = 108.35
108.35 / 12 (convert to feet) = 9.02

An "eighth-wave" would be about 4.5" long (assuming I'm remembering right - I may need to get out my radio reference...) which could also serve well - you typicallly want either a whole wavelength or an even fraction (1/2, 1/4, 1/8, or 1/16 for really low frequencies!) of the wavelength in order to tune your antenna to that band. While it may not matter so much for receiving (unless you're looking for a particular signal,) it's important for transmitting.

I may have to dig up a radio book or two to solidify those numbers (or you could get out an Amateur Radio licence handbook, or go check out arrl.com for more info,) but I'm going to be busy to-day, and it would have to wait a day or two before I could dig into it any further...
 
AM/FM + CB combined antennas are pretty much useless for CB.

Go to www.Firestik.com and read the Tech and FAQ sections for all your antenna mounting questions. Read about SWR also, you will need to check your installation when done.

102" whips fling all around on the trail and most organized trail runs do not allow them. They can bust out a window or hurt someone on the trailside watching you. Stick with a 3 or 4 foot antenna.

Get your antenna stuff at the local truckstop or from www.walcott[COLOR="Purple"]cb[/COLOR].com
 
^Thanks!

I was wondering about the reception on the steel whip. I would replace the whip with my 4' firestik when on the trail.

Do you think it would be worth my time to swap them out? Is the difference in reception worth it?
 
The difference in reception is next to nothing. A good, brand name, 3 to 5 ft antenna will met your needs. Add the height of your XJ plus 102". A 102" antenna on the roof will clank and scrape on every drive thru in town and may even hit low bridges.
 
I love my 9ft steel whip! I get better reception than any 4-5ft antenna does. The only thing I hit it on are the drive-thru's. And they are cheap...like $20.
 
Concerning the location, as mentioned, center of the roof is the best ground plane but consider spring loading the antenna because you will, at some time, forget to remove it before entering a garage or other low overhang. When installing, any extra coax should be loosely coiled as a tight coil can result in an RF choke and will impede transmission. Finally, fine tune the antenna with a SWR meter on the channel you intend to use the most; Wilson Silver Stick antenna, for example, has an adjustable tip for minimizing SWR.
 
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