i have a cobra 29 , and i have to wired to the battery of the truck ,but when i turn on the A/C i can hear the fan though the CB , and sometimes the motor

im sure its something i have set up wrong on the CB ...? or is it normal

 

Bad ground!

 

...... its all to the battery, ?

 

would running the ground to the frame help

 

Could also be interfernce with the coax cable. Run the ground as short as safely possible, and the power/antenna wire as far away as possible from fuel pump/blower fan, etc. as possible.

 

ok the wires are nexted to the frame with the battery and the coax cable is under the bed running up the fame up the cab passed the fuse box and in to the cb

 

Where's your ground for your radio?? As said above, it needs to be as short as possible. Mines a whopping 2" and it's got a ton of slack.

I don't know where your radio is located in the cab, but a place I've used for a ground is the bracket that the RCM bolts to. The RCM is under the plastic thing on the floor w/ the cupholders. This is a good ground location if your radio is in that general area.

Also, possibly move where you're taking power to a cigerette lighter or AC outlet.

 

the ground is on the neg side of the battery on the batttry and i have a tone of ground wire slack , and the radio is under the temp controls , .....i could run the ground under the floor ???

 

and my antenna its on my tool box ,

 

mines nothing like this , i just have a firestick with screw on adapter

 

That right there is thge problem that most jumps out at me. Your ground wire is probably 6 foot long. Find somewhere steel and use a self tapping screw and crimp on a small ring terminal. You want the shortest ground wire possible for your radio.

Where your radio is located, is a PERFECT spot for the ground I suggested in my earlier post. Upon finding a pic for you, you don't even have to use a self tapper....there's a ground bolt already there. Just get the correct size ring terminal(1/4" I believe), crimp it on your ground wire, and bolt it in place. This area is under your shift bezel/cupholders or if you're an auto, it's under that goofy cubby thing on the floor.

(green bolt... green = ground)







Yes, you can route wiring under carpet.

 

Other suggestions:


Toolbox mounted antennas SUCK in my experience. It's the whole reason I have the fender mount. Getting a good ground for the antenna was the main issue.

I noticed less interference when I moved the radio's positive from the battery to one of my constant hot cig lighters.

It's too late now, but like I said in the other thread, I use crimp on coax and antenna studs because they are highly suggested by all who deal with radios. Sure the screw on works okay, but eventually corrosion internally happens and that style stud/coax takes up alot of real estate.

 

that me be it , im going to try it here in a bit , i was wonderiing if it was how i had my antenna hooked up , but ill try this first

 

Try that out yeah. It's an issue that needs resolved anyway. Shorter the ground for the radio, the better.



The antenna... I could barely get it tuned to the radio....the SWR. Thankfully I run FirestikII's that have an adjustable tip for tuning, but even then, I was about maxed out on adjustability on the antenna. This was back in the toolbox mount days.

 

that did the trick , what ever i do i can not get my truck to come though the cb , even with the gain all the way up

and im going to put it on my side panel , when i get somemore time

 

@#%^&%^$#@$^% i take that back it didnt help , maybe the anntenna cord is to close to the fuse box or something

 

i think im going to have to move it off the tool box , to not get my truck to pickup though the radio , ....

 

bump

 

Run a wire from the one of the cb mounting screws (the ones on the side) to a ground. The negative power lead may be going to ground , but the radio chassis also needs to be grounded.
Years ago radio chassis began to be designed for either positive or negative grounded vehicles.
If you connect an ohmmeter between the radio frame and either power lead it will show infinite resistance.
With this isolated chassis and newer ignition systems , the noise problem has been amplified.

edit to add
I'll try to find the site again , from I believe was an Explorer forum , detailing the problem with wideband RF noise common to Fords from the fuel pump.
It showed how to construct a filter with parts from Radio Shack to help eliminate or at least allieviate the noise.

 

HF Mobile Noise Abatement

Not the one I was looking for , but may be of some help.

 

Mine was doing the same thing, and I just turned the squelch up. Maybe the simple fix is the best? hah

 

Noise is inherent to a CB because it is receiving AM Frequencies and everything electrical put out noise that is picked up on AM.

First, find out where the noise is coming from.
Start the truck, take the antenna connection off the rear of the radio, if the noise is gone then it is coming in the antenna, if the noise is still there it is coming in the power wires.

If it is antenna noise you will need to filter the noise at the source by adding power filters to each component that is causing noise.
Other than that there is not a lot you can do.
a) Add better grounding to the Antenna mount, maybe an added ground wire from the Mount to the Frame and get to bare metal.
b) Reroute the Coax
c) Move the antenna mounting location.

If it is coming in the power wires you have a few choices.
a) Re-route the power/ground wires going to the battery.
b) Add a DC Power Filter to both Power wires.
c) Add a capacitor across the speaker wires, reducing the response frequency and cutting down the noise.
d) Add an External Speaker with a Noise Suppression built in or switchable.
e) Twist the power wires together approximately 10 turns per foot and add a braided shield over both wire grounding the shield at the battery end only.

Remember these are theory ideas only, some work some of the time, some don’t work some of the time but all of them may not work at all; that is why it is called THEORY.

Luck,