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GROUND LOOPS IN MOBILE INSTALLS

loosecannon

loosecannon

Sr. Member
Mar 9, 2006
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hello to all that followed me here from the other two threads.

for anyone who just showed up here by chance; here are links to the two prior discussions that led to this thread.

http://www.worldwidedx.com/cb-band-cb-radios/29263-what-best-worst-vehicles-run-power.html

http://www.worldwidedx.com/amplifiers/30314-question-about-davemade-amps.html

please read through them in their entirety so that you are all caught up on how and why we got here, and also to avoid restating things that have already been restated after they were already stated. LOL

so, in my car, i have a cb radio going to a linear amplifier going to an antenna that is hard mounted to the roof of the car.

i have been experiencing ground loop problems since i installed the linear, in the form of the engine dying and the vehicle's computer displaying an error message.

the purpose of this thread is to learn about ground loops as they apply to two way radio mobile installs, and to hopefully get my setup working along the way.

we are basically talking about where to run the ground wires for certain pieces of equipment, and what effect the placement of these wires has on the system performance.

in the next post, i will relate what i think i have learned about ground loops so far.
(most of the info about them are for audio gear, and i think there is and will be a great need for understanding these concepts as they relate to two way radio installs in the coming years)

thanks! and read on!
 

From what I gather, you need to have all devices taking the same path to ground.

Multiple paths are bad.
 
I might be wrong, but a bus for all devices and the bus to ground is good.

Just my observation, that's how base station grounding is.
 
here is a quote of a post that Freecell made, and in it lies the answer.
our task is to apply the principles he speaks of to a specific installation, and we can begin to bridge the gap, so to speak.

Freecell said,

"(eliminate any and all instances where MORE THAN ONE GROUND CONNECTION PATH exists between any two pieces of equipment. the vehicles in question ARE NOT the problem.) the propensity of many here to grounding everything in sight is the cause of the problem. the solution is to use a central grounding point or "sink" and isolating all equipment with more than a single ground path connection between any two pieces of equipment using the engine block as the central grounding point connection.

duplicate ground paths form the equivalent of a loop antenna which gathers interfering currents and cumulative path resistance transforms these currents into voltage fluctuations. because of these loop induced voltage fluctuations the intended ground reference in the system is no longer at stable voltage potential so signals ride on the noise. the noise becomes part of the program signal and upsets the voltages used to control the ECM and hence the rough idle and stalling of the engine.

isolating these duplicate ground return paths then becomes mandatory in any effort to provide a solution for the problem that is the topic of the current thread.
to effectively deal with the problem the loop coupling created by multiple ground return paths between the several pieces of equipment must be eliminated allowing only the rf component to remain. right off hand i can think of two basic electronic components capable of this function, those being capacitors (dc blocking) and transformers (isolation) which are able to break up the paths responsible for the induced currents and the voltage fluctuations created by them.

the understanding of these basic principles and their practical application is all that is required for the flawless execution of high power installations in vehicles equipped with CPU/ECM regulated fuel, ignition, sensor, timing and other control functions."



so, from this, and the subsequent searches on the internet for info on "ground loops", i have gathered (at least i think! LOL) that we are talking about RF ground.

the part about using capacitors to isolate the equipment intrigued me, because caps will pass the RF component, but not the DC component.

so, where should we isolate what from what?

inside each piece of equipment? (seems to me that isolating the circuit ground from the chassis ground in the davemade amp wont be too simple LOL)

or do i remove the shield of my coax from where it meets the antenna's base and install a disc cap in series with it?
(this may sound dumb, but there are many things about ground loops that seem idiosyncratic to me. LOL)

ok guys, lets get the discussion started.

where should the grounds go in my install of radio-amp-antenna go to, to eliminate any possibility of creating any ground loops?

lets try to discuss this only as it applies to the actual installation, as that is what will be most helpful to future readers.

ready go!
LC
 
Well, I'd guess the antenna groud is different, being a RF ground and the others being DC grounds.
 
the part about using capacitors to isolate the equipment intrigued me, because caps will pass the RF component, but not the DC component.
Click to expand...
THen why do caps have use in DC applications?

I thought it turned DC to pulse DC. Charge, discharge, repeat.
 
loosecannon said:
i have been experiencing ground loop problems since i installed the linear, in the form of the engine dying and the vehicle's computer displaying an error message.
Click to expand...

Probably when "ground loop" is mentioned, they are talking about DC where two points on the same ground can have different voltage. In the case of RF amplifier, if high current is running thru the vehicle chassis, then the DC resistance various metal parts between the battery and the connection point of the amplifier become a problem. This is why both (+) and (-) power to the amplifier should come directly from the battery.

As far as whether RF power or DC current is causing your engine to die... probably the best way to eliminate one or the other is to run your amplifier into a dummy load instead of an antenna. Since the dummy load absorbs all RF energy, you will only be left with the DC power draw. If your engine still dies when transmitting into the dummy load, then you have some kind of DC wiring problem with your amplifier. If you have no problems with engine while running the dummy load, then your have RF energy messing with your vehicle computer.
 
dudmuck,

thanks for the reply.

i currently have the positive and negative cables from the amp running right to the battery.
the problem exists with the amp wired this way.

the dummy load idea sounds like a great test.
i currently only have a 60 watt dummy load, and my amp is a 4x2879, so i think i will have to buy a higher power dummy load to try that test.
i will have to wait a little while before i can buy one of those.


74IN,
i am talking about using disc caps to block DC buy leave the RF component intact.
this is what is done to isolate the PC board ground from the chassis of our cb radios.

im off to read more about this on the net.

later,
LC
 
74IN,
i am talking about using disc caps to block DC buy leave the RF component intact.
this is what is done to isolate the PC board ground from the chassis of our cb radios.
Click to expand...

But I have seen Wilsons using a cap as you said for matching.
 
i do not think that cap in the wilsons is for matching.

i think it is for RF isolation.
you are talking about a mag mount right?

LC
 
are you sure your problem isnt simply a poorly shielded car computer ? if everything was fine b4 the amp and then you started having problems that would be one of my suspects . computer error can stop the engine depending on the error . in my experience (a drop in the bucket compared to some on this forum) the only problem i ever has as a result of a ground problem was noise/static from the engine .

ive read in forums about people using copper flashing to make a shield to cover their autos computer to help "protect it from the RF signal............sometimes it helps and sometimes it dont . :(

another reason i like to run both hot and ground to components is you never know how the vehicle was constructed and if paints or protective coatings or even plastic/rubber bushings/components in the construction of the vehicle will cause grounding issues or even complete lack of ground . ground (like hot) will follow the least path of resistance .
 
[QUOTEi think it is for RF isolation.
you are talking about a mag mount right?
][/QUOTE]

Yes, but what RF isolation works for an antenna?

Of all devices in TXing, why isolate the antenna from RF?
 
TO ALL:

PLEASE!!!

if you do not have something to add about ground loops, and want to post an opinion about what else the problem might be, PLEASE go back and read ALL of the previous posts in the other two threads.

this is the third thread on this subject and i DO NOT want this to be another three page thread where everyone jumps in with their two cents without reading what has already been tried.

i do not mean any offense to anyone, but after you see what has already been tried, you will see why i say that we dont need to go over that ground yet again.

the problem i am having is because of ground loops.
that is what this thread is about, and that is where we need to keep the focus.

if you have ideas about what is contained in the other threads that does not have to do with ground loops, please reply to those threads.

thanks,
LC

PS-74IN, the caps DONT pass DC. they DO pass RF.
i am no antenna guru, so questions raised by this are best answered in the antennas section.
 
PS-74IN, the caps DONT pass DC. they DO pass RF.
i am no antenna guru, so questions raised by this are best answered in the antennas section.
Click to expand...

So forgive the F out of me.:rolleyes:
 

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