Need help picturing this chassis ground noise eliminator

GNRick

Retired member
Joined
Mar 21, 2004
Now that I have your attention, I can't figure out what this thing is supposed to look like. I guess it is more of a noise finder, not eliminator. You have a $13 Radio Shack amp/speaker and two pieces of wire. One is a RG58 cable and the other is just a 20 gauge wire. Do the pieces of wire get joined together? If so, how does that leave you with two ends for alligator clips when one end of the small wire needs a mini plug soldered on to plug into the amplifier? Maybe RC will help with the explanation. If somebody can draw a rough picture that would be great since it is worth a thousand words. Thanks.
http://www.davidnavone.com/heresHow/june2003-pt1.htm
 
Interesting set up. Basically it is measuring the difference in A/C voltage between two points on the car. Although instead of a digital read out (think DVM), it is an audible signal. Did a quick jot on some paper (click for larger image):

DSC00706.JPG

The shield of the coax and the other wire get tied together then to the ground (inner) ring on the 1/8" plug.

The coax inner wire gets tied to the tip connection of the 1/8" plug.

Solder the capacitor onto the center conductor. This cap can also be at the plug end. It doesn't have to be a crossover capacitor as stated, although it does need to be non-polarized.

To use it I would attach the 3' wire to the engine block, some may use the battery negative terminal. Then probe around the car with the coax wire. The louder the noise, the worse that part of the car provides for a ground.

Can check specific points on the car to see if they are providing a good ground. Such as the fuel tank to check it for the fuel pump.

Since the write up for this is from an car audio site, this type of set up makes more sense then just doing a voltage drop measurement with a DVM. They are looking for a 'quiet' ground to prevent noise from entering the audio system.

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Interesting set up. Basically it is measuring the difference in A/C voltage between two points on the car. Although instead of a digital read out (think DVM), it is an audible signal. Did a quick jot on some paper (click for larger image):

View attachment 176318

The shield of the coax and the other wire get tied together then to the ground (inner) ring on the 1/8" plug.




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The shield is the braded wire, correct? Do you do anything with the shield on the other side at the capacitor?
 
Not sure if its due to a stereo install ...but there is a suppression cap in the alternator that can go bad and cause noise.
 
The shield is the braded wire, correct? Do you do anything with the shield on the other side at the capacitor?

Isn't the ground the outer ring on the plug?

Yes, the outer braid is the shield. Nothing is done with it at the capacitor end. Just be sure that it doesn't contact the car when probing with the center wire. Can put some electrical tape or heat shrink around it.

By inner it is closer to the end cap where the wires enter the plug. It is the ring portion on the outside of plug, with the tip of the plug going to the center conductor of the coax.

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In a performance car, I could care less about an audio system, but I am most concerned about critical items like the fuel pump, computer, data recorder performing like expected, and needed.

The link posted clearly points out that the chassis/frame is not a good ground. Critical items must have a clean return circuit directly to the battery.

It is amazing how many owners only worry about getting more than enough power to a component, and are not diligent enough to also give it a proper ground path?

I was not smart enough to figure out some electrical gremlins in the early years, but with some research and help, we changed our method of wiring, and now have well performing and reliable systems in our street and race cars. :)
 
Nick- where have you found the best ground location to be, especially concerning the radio and an amp or two? I'm sure you've helped customers with this problem who don't care that much about racing. How about the fuel pump? Thanks.
 
Nick- where have you found the best ground location to be,......... Thanks.

When adding electrical items, we use an aux terminal board, usually 2, one for power, other for grounds.

Leads for these boards go directly to the battery.

Any GN that gets a pump hot wire kit also gets a 10 ga. ground wire from the pump connector back to the alt. :)

Race cars have power and ground direct to the battery.
 
Wow, went off topic here. GNRick, same as running power to audio amps , CD decks and stuff. Run a good ground cable back to the engine block. It is best if the audio equipment is located in the same area. This way they can 'star' off the same ground point.

That is there is an local single ground point that goes back to the engine block. And that local single point is where each piece of audio gear is grounded. This way every piece of audio equipment is referenced to the same ground.

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Wow, went off topic here. GNRick, same as running power to audio amps , CD decks and stuff. Run a good ground cable back to the engine block. It is best if the audio equipment is located in the same area. This way they can 'star' off the same ground point.

That is there is an local single ground point that goes back to the engine block. And that local single point is where each piece of audio gear is grounded. This way every piece of audio equipment is referenced to the same ground.

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Ok thanks Richard. Just for fun I put together that ground gizmo, will see how it works tomorrow. I did it just like your picture showed, with a little help from a friend. So you would run a ground wire from the trunk to the engine block? I assume you would also ground the radio at the same point?
 
If the equipment is in the trunk, yes, run a large ground back to the engine block. Can use the passenger side wiring chase, easy to access it by removing the door sill plate. It is right there under the carpet. A little tricky getting it open, as it clips together the entire length.

The other thing about all of this is to isolate the equipment cases from the car body. Most audio gear has the ground to it also connected to the outer case. The case should only be grounded via the ground cable, not also to the body.

This can make it tricky to isolate the radio case. As usually they get bolted right the dash frame, which actually provides the ground for it (stock radio). Can use a separate ground to it that goes to the same point on the engine block.

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Today I connected a ground wire from the amp to the test cable with the alligator clip. I tested different areas of the frame, body, firewall, top bolts on engine, alternator bracket, pass. front of engine where the ground cable is bolted on.....got the same loud sound out of the speaker in every spot. I'm thinking maybe because the radio is grounded with the factory wire and there is a ground loop? Tomorrow I'll disconnect the radio ground and connect it to the amp ground and see what happens. I wonder how the antenna ground figures into this?
 
If you connect the test box ground to the coax cable test probe what kind of noise/sound is there? It should be quiet.

The radio antenna coax should only be grounded at one end. Most likely the radio end. With the mast end not being connected to anything.

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