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Does a CB radio chassis need to be grounded?

Lo/Dx Frontier

Lo/Dx Frontier

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May 28, 2023
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Saw a video where a guy demonstrated noise being reduced simply because he touched the radio with his hand. He said the body of the radio needs to be grounded and it will help reduce noise. He suggested just removing one of the screws from the sheet metal of the cover and use a ring terminal under it to run a wire from that screw to the frame of the vehicle. I’m planning to do this on my radio when I install it. Does anyone else do this or recommend it?
 

groundwire said:
Not really necessary. But if you do (and its good practice), it needs to be an earth rf ground, not a common dc ground. Dc ground the cabinet will set you up for all kinds of ground loop problems.
Click to expand...

Right. He said that in the video also, and I plan to do it. I just want to understand it better.

What I comprehended from the video was not to simply fasten the chassis ground to the DC power ground, but instead run it to the vehicle frame. What I don’t understand is what difference it makes. Eventually all the grounds in the vehicle end up at the same place anyway, at the negative side of the battery. So if I run the radio’s DC ground to a nearby screw in the dash, and run the radio chassis ground way down to the frame somewhere, far away from the DC ground connection, electrically this is still the same. I could read continuity between those two points on a DMM. So how is that better than simply fastening the two together on the same screw in the dash? What makes the difference?
 
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Lo/Dx Frontier said:
Right. He said that in the video also, and I plan to do it. I just want to understand it better.

What I comprehended from the video was not to simply fasten the chassis ground to the DC power ground, but instead run it to the vehicle frame. What I don’t understand is what difference it makes. Eventually all the grounds in the vehicle end up at the same place anyway, at the negative side of the battery. So if I run the radio’s DC ground to a nearby screw in the dash, and run the radio chassis ground way down to the frame somewhere, far away from the DC ground connection, electrically this is still the same. I could read continuity between those two points on a DMM. So how is that better than simply fastening the two together on the same screw in the dash? What makes the difference?
Click to expand...
Ok mobile is a whole other deal. In a mobile setup there is no need at all to ground the chassis of any radio equipment. The rf ground is happening via the transmission line braid to the body ground. In a mobile installation, if you start running ground straps from cases to ground, you will 100% start causing ground loops. In a mobile, pos /neg pwr, mount radio, install transmission line and make sure antenna mount is grounded good and thats it. Roll with it. Broadcast station (base station) rf grounding is a whole other ballgame and it must be done right or it wont work. Which is for static electricity drain and lightning strike avoidance. Nothing more
 
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Lo/Dx Frontier said:
I’m planning to do this on my radio when I install it. Does anyone else do this or recommend it?
Click to expand...

https://www.k0bg.com/

K0BG's site is full of great info on just about all things mobile. It says for "Mobile Amateur Radio Operators", but RF is RF and the info is relevant to 11m too. It may help you to do things right the first time, saving you time, money, headaches. And have a better mobile set-up to boot.

Good luck and 7 3
 
Lo/Dx Frontier said:
Right. He said that in the video also, and I plan to do it. I just want to understand it better.

What I comprehended from the video was not to simply fasten the chassis ground to the DC power ground, but instead run it to the vehicle frame. What I don’t understand is what difference it makes. Eventually all the grounds in the vehicle end up at the same place anyway, at the negative side of the battery. So if I run the radio’s DC ground to a nearby screw in the dash, and run the radio chassis ground way down to the frame somewhere, far away from the DC ground connection, electrically this is still the same. I could read continuity between those two points on a DMM. So how is that better than simply fastening the two together on the same screw in the dash? What makes the difference?
Click to expand...
The difference is you are trying to create a path for RF to ground (or in this case the vehicle chassis). DMM's use DC to test resistance not RF. If you google "RF skin effect" you will find the RF travels on the surface of a conductor not through the middle of it, so a wide copper strap or braiding will provide more surface area for RF to travel along, and therefor a lower resistance path, than your DC ground wire.

Your radio is already DC grounded twice (unless using a mag mount) so adding another is not going to achieve anything. If you touch your radio and the noise level changes, that is indicating an antenna issue that needs to be addressed. If you are picking up extra noise when the vehicle is running compared to when the engine is off then that is an interference issue. Some ferrite chokes on the power cable or antenna lead can help with that sometimes. Lots of info on the k0bg site to read up on regarding that.
 
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