Why is my CB making noise when in reverse?!?!

[fireball]

Expo- this is driving me nuts! I've got a Cobra 75 handheld CB. I had it tied into the 12V outlet in the center console, but was getting a loud static sound when the truck was in reverse. So I added a 2nd ground to a nearby bolt. Still got the noise! Last night I wired the CB into my aux battery panel. Thought that would lick it, turned the truck on and still get the terrible squeak/squalk/whatever when in reverse. What's the deal?!?!

Please help. This is super annoying!

 

[cruiseroutfit]

I'm suspecting your getting some feedback from the lightly shielded reverse switch wiring that is right in that neck of the woods. Potentially compounded by pulling wire from a place that could have noisy power via fuses and other items on the same circuit. I generally recommend going direct to the battery or to a dedicated aux. fuseblock for communication gear as engine noise and interference seems common with tapped setups. Even direct to the battery I got a little wiper motor feed back in my Tacoma with the 75WXST, it wasn't enough to prevent legible comms but enough to notice. My FJ40 had bad engine RPM related noise with the same CB as well. I'm a big fan of the 75WXST for simplicity and a zero real estate approach in the cab however they seem more sensitive to noise and interference than others?

 

[4x4junkie]

Hard to tell in your pic what it's mounted to... Is that screw holding the radio chassis grounded directly to the truck body? (and the radio's ground (-) lead also to the body?) If not, maybe that can help.
Agreed, best to get your (+) power for the radio directly from your battery (at the battery if possible).

I've never been a fan of the 75 myself either. All it's circuits crammed into that tiny little box tends to compromise the radio's performance in several areas.

 

[fireball]

Thanks for the quick responses. The photo above shows the current mounting position but the original wiring. I just tapped into the power and ground wires that go to the 12V socket inside the center console. Step#2 was to add an aux ground under the bolt you can see on the left side of the first photo. Step #3, which I did yesterday, was to run a power and ground wire directly from the aux battery sub panel in the cargo area to the CB. I also still have the aux ground strap under the bolt. And yes, I do believe the chassis of the CB is screwed to the metal bracket of the car which is grounded.

Any other ideas or suggestions? I really have to move it as I'd then have to move the antenna wire and mic mount area.

FWIW it seems to function perfectly fine at all other times. No other interference that I noticed. But boy, that loud squalking in reverse is terrible! I've been trying to pick really good lines and make it over every obstacle the first time so I don't have to listen to it

 

[wrcsixeight]

I am not familiar with CB's or their connectors, but I thought they are BNC connectors.

Perhaps the following product, or similar, could help?

http://www.smarthome.com/70431/Enforcer-In-Line-BNC-Ground-Loop-Isolator-VG-1C12AQ/p.aspx

I have A GLI on my 3.5mm stereo mini plug for my mp3 player. It used to Humm when charging and listening to music. The GLI eliminated it. Now I use my Smartphone as an Mp3 player through my stereo. Never any buzzing or humm when charging.

Tapping the nearby circuits for hot or ground is almost a guarantee of a ground loop. Twisting the power leads if they run in parallel can help too, as well as ferrite cores.

 

[4x4junkie]

http://www.smarthome.com/70431/Enforcer-In-Line-BNC-Ground-Loop-Isolator-VG-1C12AQ/p.aspx.

That won't help for a CB, it's made for a video feedline (completely different frequencies of operation).

Thanks for the quick responses. The photo above shows the current mounting position but the original wiring. I just tapped into the power and ground wires that go to the 12V socket inside the center console. Step#2 was to add an aux ground under the bolt you can see on the left side of the first photo. Step #3, which I did yesterday, was to run a power and ground wire directly from the aux battery sub panel in the cargo area to the CB. I also still have the aux ground strap under the bolt. And yes, I do believe the chassis of the CB is screwed to the metal bracket of the car which is grounded.

Any other ideas or suggestions? I really have to move it as I'd then have to move the antenna wire and mic mount area.

FWIW it seems to function perfectly fine at all other times. No other interference that I noticed. But boy, that loud squalking in reverse is terrible! I've been trying to pick really good lines and make it over every obstacle the first time so I don't have to listen to it

Do you know what is turning on in reverse that's creating the noise? (I can't see how backup lamps would cause interference... unless you have LED ones mounted or something)...

Maybe try to narrow down where or how the noise is getting into the radio...

1. Does the noise go away when the volume control is set to minimum?
2. Does the noise go away if you disconnect the antenna cable at the radio?
3. Does the noise go away if you remove the antenna at it's outside mount (cable still connected between mount to radio)?
4. Is the noise not present if you touch only the ground (outer part) of the antenna cable connector to the radio's chassis?

Answers to these questions should help in determining further suggestions...
If the answer is yes to all 4 then you'll need to find the actual source of the noise, as the noise is being picked up by your antenna and not the radio's wiring. It's also possible relocating the antenna itself may help, depending on where it's currently mounted.

 

[fireball]

4x4, thanks for the quick and helpful reply! I was hoping you'd have a quick and easy answer though

Will have to dig into this one night this week, fun wrench turning time is over for the weekend!

 

[pidge]

Funny this topic comes up. I posted the very exact question an hour prior on my local nissan board ( http://www.cdn-ntc.ca/phpBB3/viewtopic.php?f=7&t=5412 ). 4x4Junkie can you elaborate more with the LED theory please. I asked about those possibly attributing to the noise, but don't know for sure. Thanks Pidge.

 

[fireball]

I do have LED back up lights that I installed awhile back. I also have an aux halogen fog/backup light but it can be switched off and I don't think it effects things.

Also, the noise occurs the same when the antenna is installed vs. not.

Incidentally I had this same CB installed in a similar location in my 4R with no noise issues.

 

[4x4junkie]

Also, the noise occurs the same when the antenna is installed vs. not.

Ok, so this indicates there's some possibility your antenna mount may not properly grounded, and/or you have a bad coaxial cable (shield not grounded at the radio connector).

Have you checked your SWR and is it good? Where & how is the antenna's mount mounted (got a picture?)?


On the LED light thing... Most, if not all, LED lamps use an electronic high-frequency DC-DC switching circuit to drive the LED chips at a constant current. These switching circuits can create radio frequency interference (squealing noise or even just plain static) if they are not shielded well. If a radio receiver (or it's antenna) is located near the lamp or it's wiring, noise can be picked up, interfering with received signals. There are ways to reduce or eliminate this interference (aside from relocating the antenna away from the light), though in more cases than not it requires disassembling the lamp to install a filter of some sort inside the housing. Sometimes you can also put a filter choke right on the lamp's wire next to where it enters the housing, however this tends to be less effective than something inside the lamp itself (you'll need some knowledge of electronics to know where in the circuit to put say, a couple 0.01µF disc capacitors).
It might be easier to just put an auxiliary (or disable) switch on them so you can switch them on only when you absolutely need then (or swap over to halogen lights, as they don't produce any interference at all).

 

[ExploringNH]

The guy above me is correct. To put it simply, LEDs are powered by current and not voltage. They use an electronic "driver" to create this steady current. The driver creates noise in the electrical system. Unplug your LED reverse lights and I can almost guarantee that the problem will go away. Even wiring directly to the battery does not fix the problem in many cases.

 

[fireball]

Awesome. I'll start by removing the led reverse lights and go from there.

 

[pidge]

Gheeze thanks a lot for your insight 4x4Junkie and Expor.NH. I wasn't aware that those lights do that at all. And I hope the OP dosent mind the thread jack. Thanks again.
Pidge.

 

[cruiseroutfit]

Yup, 99% chance your LED's are the culprit. Oddly enough my PFran LED's don't cause any noise nor do my ARB LED spotlights however I have a lightbar that causes a pretty horrid noise on both the CB as well as 2M and standard AM/FM as well. Bad enough that I don't run it if I need radio comms.

 

[fireball]

I have pfran LEDs inside and the Cree reverse lights.