CB Issues

[NJFJ40]

I have a portable Cobra 38 WXST CB and am having some issues. This unit can run on internal battery power or via DC-hardwire (I tapped into dome light). It can use its stubby portable antenna or the coax I ran from a firestik mounted on the rear tire carrier. Issue is a humming noise I get when the truck is running. It happens regardless of whether its using the DC-source or running on internal batterys and whether or not its using the stubby-antenna or firestik remote antenna.

This leads me to believe its not necessarily the DC ground or the antenna ground since problem exists when used portable and goes away as soon as engine is turned off. Seems like something is 'leaking' into the radio from the engine or electronics. I tried shutting off the fan, radio, lights, GPS, etcc... and no difference.

Anyone have any ideas where some common sources would be to cause this interference?

AndrewT

 

[CDN_Cruiser]

Tends to be quite common especially with lower quality receivers (most CBs) which are prone to interference. It is likely parts of the engine electronics / distributor / wires / plugs, etc. You can usually buy filters from radio stores that are typically wired into the power leads (from the battery). No real easy / cheap solution - eg better quality radio, working to shield various parts of the engine ignition system, etc.

Sorry, as I look at your sig - is this the 40? Likely still engine electronics, but not fuel injector! Same problem on all the trucks?

 

[BC_FJC]

There are normally 2 sources of noise one being power(easily solved) and the other electrical interference(Harder to fix). From what I understand you are getting the noise when the radio is not using the trucks battery. there for you are looking for electrical interference.

Try moving around the truck with the radio running on it's own DC power with the rubber ducky antenna and see if you can find the source of the noise by moving it close to different electrical items. Once you identify the item that is leaking noise you have to find a way to correct it... The hard part. check for lose cables proper grounding bad brushes in motors... the list go's on and on.

I know my wiper motor is a big source of interference that I have been working on minimizing. I have now installed a choke just before the motor to minimize the feed back when the wiper motor is running. I think this has been about 80% effective for me.

If you have a local radio shop they could probably help you identify and correct the problem. both CB and HAM radios are affected by this so go ask the HAM shop they have all the cool stuff.

Some humming noise is normal and you will need to adjust your radio to compensate.

Hope this helps a bit

 

[NJFJ40]

Thx for the input. I did notice that the noise starts at the ACC position on the ignition - the last position before the car starts to crank. So, car DOES NOT need to be running - just key in ACC position where all the electronics start but before the car actually cranks. I assume that narrows down things a little.

Only wiring I did not do on this thing is the aftermarket headunit that CircuitCity monkeys installed. I already know they wired it wrong as I lose all presets after the car is off for a while. I am now concerned they did other things wrong though I have no noise in the stereo which is common if you have bad wiring/ground. I may pull the radio fuse and see if that does anything. I will also try it in the wife's Honda and see if it does the same thing.

AndrewT

 

[NJFJ40]

No noise when used in my wife's car or my in-law's rental thats out in the driveway right now. I also pulled the radio fuse and no impact so I don't think thsts it either.

Must be something from the engine. Maybe fuel pump or alt.

AndrewT

 

[BC_FJC]

just move the antenna around and listen to see where the noise is most intence. Happy hunting

 

[NJFJ40]

just move the antenna around and listen to see where the noise is most intence. Happy hunting

Yup - good idea. I moved it around within the cab and very big differences in noise level just depending upon where the radio is in the cab. Its definitely noise leakage into the antenna as it does it via the coax lead and via the stubby to a lesser degree (portable antenna is weaker). When I remove the antenna, no noise which means its not via the power source (which I kind of knew anyway since noise happens also when I run on internal battery).

I also ran a 10 gauge cable from my battery ground direct to the antenna mount point and no difference so don't think its the antenna ground point.

I'm thinking fuel pump. Maybe need to find a way to ground the tank or something. When I turn key to ACC, the noise starts for 1 sec and stops - then starts again when I crank the engine.

Will keep trying.

AndrewT

 

[MoJ]

When I turn key to ACC, the noise starts for 1 sec and stops



AndrewT

Fuel pump priming itself.

 

[NJFJ40]

Fuel pump priming itself.

Dude - you got it. I pulled the fuel pump fuse and noise goes away. This is on my '04 Disco. The fuel pump is in the tank.

Any ideas how I can eliminate this noise? Is this a grounding issue? If so, how do I better ground the tank assembly (I think the stock tank is poly and not metal - so not sure how you ground them).

AndrewT

 

[BC_FJC]

you can try putting a chock on the power feed as close to the tank as posible this will stop it from acting like an antenna... it helped me with my wiper motor but didn't fix it 100%... after that is when the real fun starts and it normaly starts to cost $$$

 

[NJFJ40]

you can try putting a chock on the power feed as close to the tank as posible this will stop it from acting like an antenna... it helped me with my wiper motor but didn't fix it 100%... after that is when the real fun starts and it normaly starts to cost $$$

Great - whats a chock?

 

[BC_FJC]

ferrite chokes, RFI filters.... here are a few pics. Most electronc stores and radio places should have these...