CB Install help

[Morpheus]

So part of the new bumper was a CB anenna mount. I went with a 3 foot fibreglass whip with a clamp mount.



It doesn't seem to be working very well.

Lots of static, can't really hear anyone very well.

Before I start fiddling with it, I thought I'd ask for some input.

1st thing that came to mind, is that the antenna's not grounded properly, becuase the mount location got painted with the rest of the bumper, but before I go scraping paint off metal, I thought I'd ask for some advice...

What else should I be looking at?

[Simon]

The ground is a definite possibility. You can put a ring terminal on the base of the antenna, and run the wire down the swingarm to a ground location, or just scrape off the paint at your mount location.

[Snafu]

I also hear that you could tune your antenna (I need to do this). Is it "Just CBs" that can do it?

[medic]

You only need to tune an antenna if it's a custom job. Commercially purchased antenna and cables are good to go. If you made your own cable, or modified it, you may have some issues with that. That is why CB cables come in 3 ft lengths.

I had this issue before, and as mentioned had to do with the grounding. Like Simon mentioned, ensure the O ring is there and that the mount is in contact with the grounded vehicle.

Hope it helps

[Sgt_B]

Lemme guess - it receives ok, but transmits like crap, right? My first suggestion would be to move your antenna...

Antenna placement is (IMHO) probably the first thing overlooked - and your choice is something I see all too often (I always laugh at how jeepers with this setup can't talk to anyone in front of them, and all of us behind them can hear their frustration as they try to tell the trail-leader to hold-up) . If you look at military vehicles, most will have the antenna as high up as possible - which is great for comms. We'd love it to be otherwise, since a whip antenna bouncing around above the bushes, is also pretty good at attracting enemy fire, but it just isn't the case...

Receiving is pretty easy - any wave striking the antenna will cause it to oscillate, and the tuner simply "tunes into" the vibrations we tell it to care about. In order to set up a transmitting antenna however, we have to visualize wave propagation. If we imagine placing the whip through the hole of a donut (and then the donut grows to the size of an inner tube), you can visualize how a wave is radiated outward horizontally, from a vertical whip. So ideally, what you want, is an unobstructed, 360 degree view of the entire whip, with a flat surface under it to launch the wave.

Looking at your setup (again - not meant to criticize - lots of guys do this!) most of the front facing signal that your whip generates is going to be reflected back into the whip; same with a lot of the rear facing stuff (you've got a 36" antenna, and probably the lower half of it at least is blocked by a combination of thick rubber and steel). You might have a half decent signal out the sides right now, but I'd suspect the noise being generated elsewhere is enough to drown out those side lobes. Now, if your truck was a soft-top (Jeep, ILTIS, etc..) without a spare tire in the way, you'd probably have an acceptable signal, though not a great one through the canopy rigging to the front.

And for those of you with a similar setup who are thinking, "my transmission's not *that* bad - I'll just leave it where it is...", throw an SWR meter on your rig, and tune it properly. The amount of radiated energy being reflected back into your CB will shorten your amplifier's lifespan considerably.

So, where do you put your antenna? Well, if you take a look at where Nissan decided to put the factory stereo antenna, it's probably one of the best spots, given the tradeoffs we're dealing with. In a purely comms concerned world, the center of a vehicle roof would be the best spot, but in the real world it's either interfered with by the roof-rack, or it interferes with using the roof rack to carry large objects (for me - it's canoes, so not an option). Also, on an Xterra, the factory roof rack tubes are big enough that they interfered with signal launch when I had it set up back there; it was ok, but not great. Plus, with about 8" of lift, my 4-foot whip was constantly smacking into things, and being damaged. I've now moved it to mirror the factory stereo antenna, on the driver's side. Routing the thick coax cable was much easier, since I could bring it from under the dash, across the pedals and around the driver's door hinge, then up through the DS fender to the plastic covering the windshield wipers. Under the plastic was a perfect sized hole for the antenna mounting grommet. My rear-facing signal is (admittedly) not the best since i'm transmitting through the DS A-pillar, roof & rack, but since I'm the heavy SUV with the winch (surrounded by Jeeps and Zooks), I'm typically the tail-gunner for off-roading, so I want my best signal strength to be forward facing anyway.

That said, if you're getting interference on reception, then you need to figure out if it's the set, the vehicle or atmospheric. Is the static present only when the vehicle is running? Yes - it's probably be the truck. No - it could be atmospheric, the antenna, the cable, the power to the radio, or even the radio itself. Try turning off the engine, disconnecting the antenna coax cable at the CB; if the noise stopped, it's likely coming from the atmosphere (that, or you've got vehicle power entering your antenna cable somewhere). One of these days, I'll make up a good flowchart for troubleshooting this stuff, but until then Cobra's website has some good tips here:http://www.cobra.com/index.cfm?fuseacti ... ort.FAQ#39; in the end, the best place to draw interference-free power for the CB is the battery, and you must ground everything. Try to run the radio's power along the firewall, away from coils, motors and solenoids. The radio should have a ground wire from it's outer housing into the vehicle's frame or bare sheet metal. The base of the antenna should likewise be grounded to bare sheet metal or frame, and in the case of your bumper (if you choose to leave it mounted there), you should consider having a separate ground lead running from the bumper to a frame ground. Plus, keep in mind that any extra antenna coax cable should always be snaked - never coiled.

Lots to think about...

[Sgt_B]

You only need to tune an antenna if it's a custom job. Commercially purchased antenna and cables are good to go. If you made your own cable, or modified it, you may have some issues with that. That is why CB cables come in 3 ft lengths.

I had this issue before, and as mentioned had to do with the grounding. Like Simon mentioned, ensure the O ring is there and that the mount is in contact with the grounded vehicle.

Hope it helps

I have to disagree, Medic. That's a fairly accurate statement for receiving, but if you plan to transmit, tune your antenna to your set.

Here's a good primer on the topic, thanks to the good folks at Firestik: http://www.firestik.com/Tech_Docs/TUNABLE.htm

[Rev]

is your antenna adjustable?

[Morpheus]

I've read a bunch of stuff on the net before posting here, so this is what I've come up with so far

1) my problem is with recieving, I haven't tried transmissing, becuase I've read that you can damage your radio if you have an antenna problem

2) I read that usually, you only need about 60% of the antenna above the roof. Although my 3 foot antenna is probably closer to 30%, I figured I could try it out this way first, and always go to a bigger one if needed.

3) I read a bunch about tuning the antenna, I don't believe this antenna is tuneable, I don't see any adjustment screws on it

4) It's not engine noise, I know what that sounds like

5) The cable is a pre-made 12 ft cable, just bought it, shouldn't be a cable problem

I know the bumper is grounded well, as the lights are grounded to it and they work fine, so I think I should start by grounding the antenna mount...

[Jayman]

Can you tell that Sgt_B was a Comms. guy in his former life?

GREAT post...



As for the tunability of your fiberglass whip, chopping bits off the tip with a fine toothed saw is how you do it....

[HolidayNation]

Your bumper may be grounded, but is your swingarm and therefore your ant. Mount insufficiently grounded.

[Bender]

I told you to run a separate ground wire from the antenna to the body as I knew this would come up. I had my whip on my roof basket, and ran a ground wire to the body full well knowing it would cause problems. I have also heard you can't tune fiberglass whips.

[Morpheus]

Your bumper may be grounded, but is your swingarm and therefore your ant. Mount insufficiently grounded.

The light for the plate is on the swingarm, and it's ground works fine. The mount point has about 3 coats of paint and 2 coats of primer on it. I think that's more likely my ground problem. I'm going to fix that on the weekend and go from there.

[mookie]

Your bumper may be grounded, but is your swingarm and therefore your ant. Mount insufficiently grounded.

The light for the plate is on the swingarm, and it's ground works fine. The mount point has about 3 coats of paint and 2 coats of primer on it. I think that's more likely my ground problem. I'm going to fix that on the weekend and go from there.

Be aware not to confuse RF grounding (plane) with 12v DC ground.

[Morpheus]

The light for the plate is on the swingarm, and it's ground works fine. The mount point has about 3 coats of paint and 2 coats of primer on it. I think that's more likely my ground problem. I'm going to fix that on the weekend and go from there.

Be aware not to confuse RF grounding (plane) with 12v DC ground.

Ask me to tear down an engine and change a wrist pin and I can do it with my eyes closed....

You lost me with your above statement. What's the difference.

[mookie]

Be aware not to confuse RF grounding (plane) with 12v DC ground.

Ask me to tear down an engine and change a wrist pin and I can do it with my eyes closed....

You lost me with your above statement. What's the difference.

Hi, I'm heading out the door for some long weekend camping so I can answer when i get back into town. Or perhaps someone else will chime in. Sorry about that.

[keith]

found this 2nd post in this thread
http://www.jeepforum.com/forum/showthread.php?t=716645" onclick="window.open(this.href);return false;

[mookie]

found this 2nd post in this thread
http://www.jeepforum.com/forum/showthread.php?t=716645" onclick="window.open(this.href);return false;

Yup, that should clear it up.

[mookie]

http://www.k0bg.com/ground.html" onclick="window.open(this.href);return false; - this is where I went for my HF and VHF radios. Applies to CB as well.