CB Tuning

[Kacers]

Quick question. I hooked up my CB and I get a noticeable hum on it when the car is running. Sounds fine and quiet when the car is not running - the loudish hum only starts with the engine running but does not vary as the car is rev'd.

I switched antenna coax and it doesn't matter - same thing. I also switched from DC power to internal battery power and no difference. Just noise when the car is running.

Antenna was tuned (4' Firestik) with SWR meter and is mounted to rear tire carrier with coax routed thru rear door as others have done.

Do others notice this same issue on their CB installs? Any suggestions as to where the interference may be coming from or common sources of such?

AndrewT

 

[JamesWyatt]

Run a heavy gauge power wire through the firewall directly to the positive battery terminal. Use an inline fuse close to the battery. Make sure your ground is bulletproof. Solder all your connections.

On the 04, you have a good sized hole with a rubber grommet in the firewall on the driver's side. It's just above the pedals - you may need to pull back the carpet a bit. You can see the grommet from the engine compartment. I removed the grommet and cut out a little hole in the middle for the wire to pass through. I then cut a radius slit from the edge of the grommet to the center hole. Works great, and you can seal it with that black putty stuff from the engine side to keep water out when stream crossing. Also, there's a nice bolt on the firewall next to the grommet for the ground wire. Just make sure and scrape off all the paint.

 

[JamesWyatt]

To answer your question more directly, though, the noise is not your SWR or antenna. You can have the same problem with audio equipment if you jerry-rig into an existing power line.

 

[Joey]

I notice you said you even tried an internal battery source... i.e. ruling out bad electrical, sounds to me like you are getting some type of electrical interferance from the engine or electrics... try useing a ground wire from the radio to a know good ground as close as possible to the radio. If this doesn't work try picking up a power conditioner that conditions both the ground and the hot...

 

[rmuller]

I believe he has a hand held unit, which while he did hook up a power line, it may also be running on batteries only.

 

[Kacers]

Ryan is right. I have a handheld unit. So it can run off battery or DC power and it can use coax or stubby antenna. My first thought was bad ground on power or antenna so I checked that first. I have this issue with the unit running on internal battery power (no DC source from the car connected) and using the portable antenna (not connected to coax that runs to the firestik).

Joey - when you said "try useing a ground wire from the radio to a know good ground as close as possible to the radio" - what do you mean? I did have an aftermarket head-unit installed by Circuit City and maybe they did something incorrect. Were you suggesting to verify the radio is grounded completely or were you saying something else?

I tried turning all electrics off (radio, lights, fan, GPS, etc..) and it does not stop the hum.

AndrewT

 

[Joey]

I meant the CB, but as it is a handheld.... I am not sure a ground strap would make much difference.

Either way it sounds like someone has wired something wrong, you are getting electrical noise from something and since it doesn't increase with the engine I would be at a lose with out a tuner and a scope to find the frequecy...

 

[Kacers]

I narrowed the noise down to starting when the ignition is in the ACC psoition - the key position just before car starts to crank. So, the car does not need to be running to get the hum.

I will try and pull the radio fuse as thats the only circuit in there that I did not wire myself. I know they wired it wrong as I lose radio presets when the car is off and thats not supposed to happen so.........

AndrewT

 

[rovercanus]

I got some noise also when the truck is running, not speed dependent. To help eliminate the noise make sure your attenna is also grounded properly. Don't count on the mount to ground it, use a seperate wire or strap to a ground point on the truck.
Also from my experiments, the taller the attenna is the less noise I get.
I have a 4' Wilson Super Flex mounted to the rear D-pillar on a spring mount. There is a grounding point right below it that I've run a ground wire to.
Make sure you have at least 2/3rd's of the attenna above the roof line.
I have beaten the living shit out of this attenna on the overgrown woods around here and it still is in great shape.
Also have an almost perfect swr reading with it. It a very good option to the normal Firestiks that people use.

 

[Kacers]

My Firestik is mounted to the spare tire carrier on my '04 as many others have done and as EE site posted before (link seems to gone from there now). I don't think that set-up requires a separate grounding strap though I can run one if needed.

AndrewT

 

[rovercanus]

My Firestik is mounted to the spare tire carrier on my '04 as many others have done and as EE site posted before (link seems to gone from there now). I don't think that set-up requires a separate grounding strap though I can run one if needed.

AndrewT

The rear door is grounded but it's not the greatest ground. I had mine there at one time but moved it to improve reception. Remember, the truck is now part of the anttenna, a good ground for the anttenna is essential.

 

[rovercanus]

Forgot how to spell antenna!

 

[Kacers]

I just ran a 10 gauge wire direct from battery - and to the antenna mount point for direct ground and this did not affect the issue at all. That tells me its not an antenna grounding issue.

I pulled the radio fuses and this did not help either.

I am pretty sure that the antenna is picking up some other electrical interference. Maybe fuel pump??? When I turn key to ACC, the hum starts for a sec and then stops. It only starts again after I crank the ignition and then steady on with engine running. Does the fuel pump prime itself in the ACC position? I'm thinking I may try to ground the tank and see if that helps.

AndrewT

 

[rovercanus]

Try raising the antenna then. Actually, I have a mount that will raise it about 10" or so. You can have it if you like. It mounts on the tire mount and is made from machined aluminum.
Get as much antenna above the roof line as possible.

 

[Eric N.]

Does it do this with the stubby hand held antenna while inside the truck as well without the larger antenna attached? I have a Cobra handheld that picks up some noise (electrical interference/field) from the truck while it's in the truck and not hooked up to anything.. I just adjust the squelch till it's gone and everything is fine..

 

[ptschram]

It sounds like nosie from the ECU to me. Gonna need to bypass the ECU.

 

[Kacers]

Yes - it does this with the stubby antenna mounted inside the truck. Noise is not dependent on what antenna I use (stubby or firestik).

After reading some CB forums, I am leaning towards the fuel pump as likely source of interference. ANyone have any ideas on how I can determine this? And any good ideas on how to better ground that system? I think my tank on my '04 is plastic and not metal but not sure (too wet too crawl under there now). Curious how I would go about 'grounding' the tank better as many CB sites suggest.

AndrewT

 

[Kacers]

OK - I pulled the fuel pump fuse and noise goes away. So thats the cause of interference or atleast as close as I can get right now.

Anyone have any clue as to how I can better ground the fuel pump circuit? I have a Southdown gas tank skid plate on there and and wondering if that contributes to the issue in anyway as it mounts to the stock tank/frame strap.

AndrewT

 

[ptschram]

Sounds like you need to bypass the fuel pump wiring with some capacitors to ground-similar to the noise filters for stereos.

 

[Kacers]

Sounds like you need to bypass the fuel pump wiring with some capacitors to ground-similar to the noise filters for stereos.

Yeah - did some more reading on CB forums and Ford seems to have a known issue with fuel pump circuit and RF noise. Don't know if this extends over to Rover but late model F-150/F-250s have the same issue and Ford can put something in the fuel pump curcuit to resolve. I will keep reading or try the in-line capacitor fix or just keep raising antenna to try and resolve issue. Its weird as most fuel pump issues are said to be caused when the antenna is within line-of-sight of the fuel pump. Mine isn't really and many other Disco owners mount them the same as I did but who knows....

One other comment said the Wilson 1000 antennas reduce or remove fuel pump noise altogether. For $20, I may just get another antenna and check that out as its alot easier then opening up the fuel tank.

AndrewT