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GROUND LOOPS IN MOBILE INSTALLS
- Thread starter loosecannon
- Start date
See my problem with that is that they are all tied together to the vehicle ground so why does it matter where it is connected?
And then this would be where bonding with braided strap would come in.
RF can be a fickle critter.
Capacitors do pass AC, do not pass DC. There's almost always some AC component in DC charging systems, so using capacitors to 'pass' that AC to ground rather than to equipment isn't a bad idea. Commonly called 'by-passing', and to some ridiculous point, bigger is better.
Capacitors are also used in 'matching' impedances/antennas. That's a completely different thingy. The value of a particular capacitor determines the capacitor's 'reactance', which means how it will react to RF at some frequency. That characteristic is taken advantage of when capacitors are used to change an antenna's characteristics (tuning it).
Each and every installation is different. Some require more 'effort' than others, different 'strokes' for different 'folks' sort of thingy. Doing something one way doesn't work well? Try it another way. From there, I'm not beating on that 'dead-horse' grounding issue.
Something that you also have to take into account is that some vehicles are not as susceptible to RF 'poisoning' as are others. The manufacturer just didn't do as good a job as they could have, or they just didn't figure it was needed. If the motor dies, or other weird things happen, it's probably RF getting into the vehicle's CPU. The first thing to try is lowering power output. If that helps, then shielding, by-passing, yada yada yada some of that. Most automotive manufacturers have information for that. Finding it is the 'trick', good luck!
- 'Doc
Capacitors are also used in 'matching' impedances/antennas. That's a completely different thingy. The value of a particular capacitor determines the capacitor's 'reactance', which means how it will react to RF at some frequency. That characteristic is taken advantage of when capacitors are used to change an antenna's characteristics (tuning it).
Each and every installation is different. Some require more 'effort' than others, different 'strokes' for different 'folks' sort of thingy. Doing something one way doesn't work well? Try it another way. From there, I'm not beating on that 'dead-horse' grounding issue.
Something that you also have to take into account is that some vehicles are not as susceptible to RF 'poisoning' as are others. The manufacturer just didn't do as good a job as they could have, or they just didn't figure it was needed. If the motor dies, or other weird things happen, it's probably RF getting into the vehicle's CPU. The first thing to try is lowering power output. If that helps, then shielding, by-passing, yada yada yada some of that. Most automotive manufacturers have information for that. Finding it is the 'trick', good luck!
- 'Doc
LC -
"Ground loop" is the term used to describe situations occuring in ground systems where a difference in potential exists between two ground points. Ideally, a ground is a ground is a ground. But for this to be true, ground wires with zero resistance are necessary. Real-world ground leads have finite resistances, and the currents running through them will cause finite voltage drops. If two ground returns tie into the same line at different points there will be a voltage drop between them. These voltage differences can cause phase-shifts, feedback, and other problems. The solution to ground loop problems is to always use a single-point ground system.
To avoid ground loops in any mobile installation, it is imperative the power connection ground lead for each piece of the radio equipment be tied to the same central grounding point. In vehicles with on-board ECM control, the ground point that you use has to be the same as the ground point for the ECM system. Otherwise you will have ground loop problems, and the operation of the ECM will be adversely affected. In your mobile, Freecell pointed out that the engine block was the ground point (reference ground) for your ECM system, so the grounds for the radio equipment DC power lines should be attached there. On vehicles made by other manufacturers, the reference ground point may be different. A good rule to follow for all mobile installs is to connect all power leads to the same points: i.e. hot leads to battery positive terminal, and ground leads to central ground point (reference ground). Always keep the leads as short as possible. A final rule is to make all ground leads low resistance and low inductance by using large diameter wire.
Also, I always install bypass capacitors across the power leads as close to each piece of radio equipment as possible. I use two caps for each piece of equipment. A high value electrolytic to knock down the noise on the positive dc lead, and a 220 pf npo to shunt any stray rf on the positive lead to ground. The electrolytic's value depends on the equipment. For CB radios I use at least 10,000 uf or more. On linears, I use a one-farad cap available at car stereo stores for use with high power car stereo boosters. The electrolytics filter out general noise on the power lead, quiet down the receive, and act as current sinks which help hold the vehicle system voltage steady under peak current draw.
Oftentimes, ground loops are mistakenly blamed when a vehicle runs rough, dies, or whatever when a high power rig is keyed up. In many vehicles, the electrical system can barely supply enough current to keep the vehicle and all of its accessories running. Add a two-way radio and a current-hungry high power linear and you have real problems. If the battery/alternator combo can't keep up with the needs of both the vehicle and radio, the electrical system voltage will drop and both vehicle and radio performance will suffer. The problem is compounded if you're working sideband as the voice signals will draw "bursts of current" from the vehicle electrical system and the system voltage will fluctuate all over the place. These voltage fluctuations can drive an ECM system crazy. Remember what you said about there not being a problem when you dead-keyed, but only when you modulated?
The ultimate is to install a complete auxuillary charging system (alternator, voltage regulator and battery) just to power the radio stuff.
- 399
"Ground loop" is the term used to describe situations occuring in ground systems where a difference in potential exists between two ground points. Ideally, a ground is a ground is a ground. But for this to be true, ground wires with zero resistance are necessary. Real-world ground leads have finite resistances, and the currents running through them will cause finite voltage drops. If two ground returns tie into the same line at different points there will be a voltage drop between them. These voltage differences can cause phase-shifts, feedback, and other problems. The solution to ground loop problems is to always use a single-point ground system.
To avoid ground loops in any mobile installation, it is imperative the power connection ground lead for each piece of the radio equipment be tied to the same central grounding point. In vehicles with on-board ECM control, the ground point that you use has to be the same as the ground point for the ECM system. Otherwise you will have ground loop problems, and the operation of the ECM will be adversely affected. In your mobile, Freecell pointed out that the engine block was the ground point (reference ground) for your ECM system, so the grounds for the radio equipment DC power lines should be attached there. On vehicles made by other manufacturers, the reference ground point may be different. A good rule to follow for all mobile installs is to connect all power leads to the same points: i.e. hot leads to battery positive terminal, and ground leads to central ground point (reference ground). Always keep the leads as short as possible. A final rule is to make all ground leads low resistance and low inductance by using large diameter wire.
Also, I always install bypass capacitors across the power leads as close to each piece of radio equipment as possible. I use two caps for each piece of equipment. A high value electrolytic to knock down the noise on the positive dc lead, and a 220 pf npo to shunt any stray rf on the positive lead to ground. The electrolytic's value depends on the equipment. For CB radios I use at least 10,000 uf or more. On linears, I use a one-farad cap available at car stereo stores for use with high power car stereo boosters. The electrolytics filter out general noise on the power lead, quiet down the receive, and act as current sinks which help hold the vehicle system voltage steady under peak current draw.
Oftentimes, ground loops are mistakenly blamed when a vehicle runs rough, dies, or whatever when a high power rig is keyed up. In many vehicles, the electrical system can barely supply enough current to keep the vehicle and all of its accessories running. Add a two-way radio and a current-hungry high power linear and you have real problems. If the battery/alternator combo can't keep up with the needs of both the vehicle and radio, the electrical system voltage will drop and both vehicle and radio performance will suffer. The problem is compounded if you're working sideband as the voice signals will draw "bursts of current" from the vehicle electrical system and the system voltage will fluctuate all over the place. These voltage fluctuations can drive an ECM system crazy. Remember what you said about there not being a problem when you dead-keyed, but only when you modulated?
The ultimate is to install a complete auxuillary charging system (alternator, voltage regulator and battery) just to power the radio stuff.
- 399
Last edited:
74IN,
my use of caps was not meant to be offensive.
they were just for emphasis.
i am not assuming this is a DC ground loop.
i am saying for certain that this problem has to do with stray RF getting into the vehicle's computer system.
how that is happening is the topic of discussion.
i do appreciate the interest!
and before anyone starts going off about using ferrites and common mode currents, please read the previous threads to find out what i have already tried.
if, after reading through them, you think you have something that i did not try, then by all means mention it here.
please go back and read the previous two threads, and i think you will see where i am at.
unit 399,
grounding the amp to the engine block is one of the first things i am going to try when my amp gets here.
i am trying to find out a bunch of things to try before it gets here.
one thing though, is how would you ground the antenna to the engine block?
the amp will have one ground path from the engine block, and another from the roof of the car.
i still do not fully understand all the ways in which ground loops are formed, but to me, this seems like it might create one.
TO ALL!!!!
do any of you really think that if the answer were simple, like "just ground everything to the body, duh!" that this subject would have gone on for so long?
give me some credit for having half a brain. LOL
anyone that wants to contribute an idea that does not specifically pertain to the practical application of the principles of ground loops NEEDS to read ALL of the posts in BOTH of the previous threads.
only then will you understand what i am dealing with and why the simple solutions are not going to cut it in THIS installation.
everyone is welcome to comment here, but if you havent read through the other threads, you are just re-stating what others have already said.
thanks to all, and no offense is meant to anyone,
i have but one goal. that is to get this setup working.
i know its possible, we just have to get there.
LC
my use of caps was not meant to be offensive.
they were just for emphasis.
i am not assuming this is a DC ground loop.
i am saying for certain that this problem has to do with stray RF getting into the vehicle's computer system.
how that is happening is the topic of discussion.
i do appreciate the interest!
and before anyone starts going off about using ferrites and common mode currents, please read the previous threads to find out what i have already tried.
if, after reading through them, you think you have something that i did not try, then by all means mention it here.
please go back and read the previous two threads, and i think you will see where i am at.
unit 399,
grounding the amp to the engine block is one of the first things i am going to try when my amp gets here.
i am trying to find out a bunch of things to try before it gets here.
one thing though, is how would you ground the antenna to the engine block?
the amp will have one ground path from the engine block, and another from the roof of the car.
i still do not fully understand all the ways in which ground loops are formed, but to me, this seems like it might create one.
TO ALL!!!!
do any of you really think that if the answer were simple, like "just ground everything to the body, duh!" that this subject would have gone on for so long?
give me some credit for having half a brain. LOL
anyone that wants to contribute an idea that does not specifically pertain to the practical application of the principles of ground loops NEEDS to read ALL of the posts in BOTH of the previous threads.
only then will you understand what i am dealing with and why the simple solutions are not going to cut it in THIS installation.
everyone is welcome to comment here, but if you havent read through the other threads, you are just re-stating what others have already said.
thanks to all, and no offense is meant to anyone,
i have but one goal. that is to get this setup working.
i know its possible, we just have to get there.
LC
LC -
There is a difference between RF ground and DC ground. Put one ohmmeter probe on the ground lead of your radio, and the other on the ground side of the antenna connector. They are not connected. The RF output is isolated from DC ground, as is the case of the radio. Grounding the antenna to the vehicle is to make certain that the antenna sees a good ground plane to work with for maximum performance.
- 399
There is a difference between RF ground and DC ground. Put one ohmmeter probe on the ground lead of your radio, and the other on the ground side of the antenna connector. They are not connected. The RF output is isolated from DC ground, as is the case of the radio. Grounding the antenna to the vehicle is to make certain that the antenna sees a good ground plane to work with for maximum performance.
- 399
Okay, I checked again. Got 2 ohms on one radio, all of three ohms on another. Checked chassis ground to power ground, same resistance. Figured that was from length of the power lines and not exactly calibrating the meter to absolute zero. Just for grins I also checked voltage from chassis ground to power ground. Zero in both cases.
- 'Doc
- 'Doc
If the body of the vehicle is used as counterpoise then bonding each body part together is very important for the rf path as well as shielding rf from dc ground.
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@ kingmudduck:So I have a cobra 138xlr and the meter dose not work... It dose not key up and signal dose not work.... It is not stuck it the meter moves freely. now wires are resoldered on both ends...So now that do I look at. Could it be a diode or a transistor?
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...runna pile-up on 6m SSB