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Gounding question

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Gounding question

Post by Kaos » Monday, 09 December 2013, 14:08 PM

Are CB radios and linears/amps as sensitive to grounding as car audio amps and stereos? I have wired up several car audio systems and know how finicky amps can be when it comes to grounding. Are CB's and linears/amps the same way? Do the grounds need to be as short as possible? What about grounding locations....can I ground a CB radio, linear/amp, and wattmeter(illuminated) in the same place or will I have noise? TIA.
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Re: Gounding question

Post by zygoma » Monday, 09 December 2013, 14:15 PM

If you're talking about the DC ground that all of them need as a return path to the battery for operating voltage, then single point grounding is fine. Large enough conductors from each device to the battery's ground terminal should cause a small enough difference in their paths so as to serve as a single point ground (after all, not all the devices mentioned are exactly the same distance from the battery in the first place, right?)

The SWR/wattmeter shouldn't need any ground at all, unless you're using DC current from the vehicle's electrical system to power a lamp or something. Otherwise, it's probably just a passive device and no more needs a ground than a barrel connector in the coax. Similarly, the radio and RF amp shouldn't need any other grounds besides a solid DC return path; the mumbo-jumbo about having to install RF grounds on every cotton pickin' thing from the mic to the antenna mount are wasteful of $$$ and install time, with the caveat that your antenna mount is adequately grounded to a sufficient counterpoise ("ground plane") surface on the vehicle, and the antenna is resonant.

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Re: Gounding question

Post by Kaos » Monday, 09 December 2013, 14:34 PM

zygoma wrote:If you're talking about the DC ground that all of them need as a return path to the battery for operating voltage, then single point grounding is fine. Large enough conductors from each device to the battery's ground terminal should cause a small enough difference in their paths so as to serve as a single point ground (after all, not all the devices mentioned are exactly the same distance from the battery in the first place, right?)

The SWR/wattmeter shouldn't need any ground at all, unless you're using DC current from the vehicle's electrical system to power a lamp or something. Otherwise, it's probably just a passive device and no more needs a ground than a barrel connector in the coax. Similarly, the radio and RF amp shouldn't need any other grounds besides a solid DC return path; the mumbo-jumbo about having to install RF grounds on every cotton pickin' thing from the mic to the antenna mount are wasteful of $$$ and install time, with the caveat that your antenna mount is adequately grounded to a sufficient counterpoise ("ground plane") surface on the vehicle, and the antenna is resonant.

73
Thanks for the input. Here is what I am planning. I already have a 102" whip installed w/ a ball mount. The antenna is grounded to the chassis of the truck. I am soon going to add a radio, amp, and watt/swr meter (it's a Workman HP201s w/ backlit display). Everything will be in the same area so I was going to run a wire from the battery (4 ga.) to a fused distribution block and mount it near the radio, amp, meter. That way I wouldn't have 3 different wire runs to the vehicles battery. There is also a good grounding point near the place I plan on putting the radio, amp, and meter. This vehicle already has an aftermarket audio system installed so I want to keep from running any more wires than needed (hence the distribution block and nearby ground point).

Other than the fuses for the radio, amp, and watt/swr meter not being as close to the battery as they could be do you see any problems? When I installed the audio system I ran new speaker wires down one side of the vehicle and the main power wire down the other. I have managed to keep my coax away from the speaker and amp power wires. But w/ all the wires already installed I want to keep the new ones to a minimum so I thought the fused distribution block would work.
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Re: Gounding question

Post by zygoma » Monday, 09 December 2013, 16:21 PM

Sounds like you're doing fine. I use a similar fused DC distribution block (with Anderson PowerPoles for individual loads). Each branch has its own fuse appropriate to the load of the device hooked to it. Way back at the battery end of the "big red", one huge fuse, rated for the maximum current of the capacity of the feeder from the battery to the panel is installed right next to the battery, to protect against a catastrophic short to the big wire at the firewall or someplace else along its route.

As long as your coax is well shielded, there shouldn't be any substantial problem with RF leakage from the coax into the stereo speaker cables. If there is, you can always install low value bypass capacitors from each speaker lead to ground to bleed off any RF that does get induced into the speaker wires.

Don't cheap out on the power distribution hardware -- tight connections, low resistance metal plating on fasteners & cable connectors, etc., a light treatment with De-Oxit as a prophylactic against future corrosion and/or other high resistance (and therefore noise inducing) stuff happening.

Sounds like you're on the right path. BTW, by "ground at the antenna", I assume you mean the part of the mount that's attached to the shield of the coax, and not the hot side ("radiator"). Actually grounding the antenna, assuming you don't have a shunt fed antenna, is a good way to waste all that energy (RF and otherwise) by just dumping it back into an RF dead short.

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Re: Gounding question

Post by Kaos » Monday, 09 December 2013, 16:38 PM

zygoma wrote:Sounds like you're doing fine. I use a similar fused DC distribution block (with Anderson PowerPoles for individual loads). Each branch has its own fuse appropriate to the load of the device hooked to it. Way back at the battery end of the "big red", one huge fuse, rated for the maximum current of the capacity of the feeder from the battery to the panel is installed right next to the battery, to protect against a catastrophic short to the big wire at the firewall or someplace else along its route.

As long as your coax is well shielded, there shouldn't be any substantial problem with RF leakage from the coax into the stereo speaker cables. If there is, you can always install low value bypass capacitors from each speaker lead to ground to bleed off any RF that does get induced into the speaker wires.

Don't cheap out on the power distribution hardware -- tight connections, low resistance metal plating on fasteners & cable connectors, etc., a light treatment with De-Oxit as a prophylactic against future corrosion and/or other high resistance (and therefore noise inducing) stuff happening.

Sounds like you're on the right path. BTW, by "ground at the antenna", I assume you mean the part of the mount that's attached to the shield of the coax, and not the hot side ("radiator"). Actually grounding the antenna, assuming you don't have a shunt fed antenna, is a good way to waste all that energy (RF and otherwise) by just dumping it back into an RF dead short.

73

Thanks for the help. I'm not sure I understand what you are saying about grounding the antenna. Below is a picture of what my mount looks like. I ran a ground wire to my chassis from the same bolt that the black wire in the picture goes to. I thought that's how it was supposed to go....was that right?

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Re: Gounding question

Post by De_Wildfire » Monday, 09 December 2013, 16:55 PM

It looks like you are on the right track here. I have a base and all my radios are grounded including my tube amp, antenna tuners, coax switch box, and MFJ current DC outlets. I don't have my computing SWR/PWR meters grounded though. If I had do do it in the car, I would hook up all my equipment to a DC high current outlet with fuse protection and then go to the batttery and I think it was mentioned already. Then I would find a good ground and connect my equipment to it if it were mobile. On the base, I have little two inch braded ground strap bridges from equipment connecting to a longer braded ground strap that goes to a 8 foot copper rod below the foundation of the house.

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Re: Gounding question

Post by MDYoungblood » Tuesday, 10 December 2013, 12:27 PM

Grounding the case of the radio would not be needed if the mounting bracket is in a place where it is fastened to metal, if it is in plastic then it would be a good idea to add a wire to a case screw. If you look inside most radios they only have a small capacitor from the negative side of the PCB to the case just to bleed off stray RF but is not really good enough to make a clean ground. The negative wire lead is not a case ground unless it is physically attached to the case. Same thing goes for an amplifier. Grounding your radio in the vehicle and at home can help in reducing man made noises likes transformers for furnace, doorbell, engine noises, and can help in reducing bleedover on some other electronics in the house. Grounding is a matter of opinion, some do and some don't, I am one that does.

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Re: Gounding question

Post by Kaos » Tuesday, 10 December 2013, 12:39 PM

MDYoungblood wrote:Grounding the case of the radio would not be needed if the mounting bracket is in a place where it is fastened to metal, if it is in plastic then it would be a good idea to add a wire to a case screw. If you look inside most radios they only have a small capacitor from the negative side of the PCB to the case just to bleed off stray RF but is not really good enough to make a clean ground. The negative wire lead is not a case ground unless it is physically attached to the case. Same thing goes for an amplifier. Grounding your radio in the vehicle and at home can help in reducing man made noises likes transformers for furnace, doorbell, engine noises, and can help in reducing bleedover on some other electronics in the house. Grounding is a matter of opinion, some do and some don't, I am one that does.

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Greg
Thanks for the info. The radio (General Lee) will be mounted in a steel Workman adjustable base that will be screwed to the body of the truck. Do you think that will be sufficient? The Workman base is painted.

With a lot of experience in car audio I know the frustrations improper grounding can cause. But just about all of my experience is trial and error so if I have the option I like to ask others that may know more.
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Re: Gounding question

Post by MDYoungblood » Tuesday, 10 December 2013, 15:37 PM

When painted surfaces are involved I use this type of washer, they dig into the metal through the paint.
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Re: Gounding question

Post by 721HACKSAW » Tuesday, 10 December 2013, 16:52 PM

I'm an old Industrial Electrician, yet I still remember the words of my old trade teacher years ago... He taught you did not use the term "ground" in this situation, it is an electrical "bond"

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Re: Gounding question

Post by MDYoungblood » Wednesday, 11 December 2013, 12:35 PM

Yes you are right and that is a very good term to use in automotive installations because there is no physical connection an earth ground. Thing I will start using it , "bond". Thanks 721HACKSAW.

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Re: Gounding question

Post by rickk » Wednesday, 07 May 2014, 14:40 PM

I'm sure you will get many opinions on this...

Mine would be to run both hot and ground as directly to the battery terminals as possible.

If you are running an amp, run the amp wires separate from the radio wires for the entire run.

If you combine them, as the amp draws current, any voltage drop that it creates in the wiring will show up at the radio's power wires. At modulation peaks, when the current will be the highest, the radio input voltage will be the lowest. That is not what you want to happen.

Run separate wires so that voltage drops are independent. The radio will have a more stiff voltage source to at least drive the amp hard on peaks.

Rick

-- Friday, 27 June 2014, 10:37 AM --

One other thing... if you run a ground wire to the battery, make sure there is a fuse in it.

You will often see a fuse in the ground lead of automotive equipment. At first glance, it doesn't make sense for it to be there.

However, if you have some ground issues in your vehicle (like a bad battery ground cable), you may suddenly find something weird happening like some to most to all of the engine starter current trying to make it's way back to the battery under cranking conditions via the ground wire on your amplifier. That wont work well and in fact there would probably be a fire. A fuse in the negative power lead will save a lot of grief if this was to happen.

Rick


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