Baluns and Ground Loop issues

[empak 0]

I know there have been threads around about baluns and ground loop problems, but I haven't found any understandable explaination of the problem.

 

 

koolmer

 

You did not state if the systems were active or passive baluns, I have found that Interference ground loops are more comon on passive systems running 12v DC,over the ones with 24vAC, even the AC systems can be a victim of the loop or hum bar. Interference is the addition (superposition) of two or more waves that results in a new wave pattern. Cable path seems to play a big part in this, wireing runs that are close to large AC runs, AC Motors and lighting balast. try turning off all the power in the building if you can, execpt for the video eqipment, if you still have a loop its your equipment, if not turn the breakers on one by one at see what causes your interference loop. I always have a four way Acitve receive Balun to test to signal on, most cases it seems to remove the humbar and bad video from the loop.

[Soundy 1]

I know there have been threads around about baluns and ground loop problems, but I haven't found any understandable explaination of the problem.

 

 

koolmer

 

You did not state if the systems were active or passive baluns, I have found that Interference ground loops are more comon on passive systems running 12v DC,over the ones with 24vAC, even the AC systems can be a victim of the loop or hum bar.

 

With AC cameras, it's more likely the existence of an additional ground path, particularly if the cameras are mounted to something metal that's also grounded.

 

Interference is the addition (superposition) of two or more waves that results in a new wave pattern. Cable path seems to play a big part in this, wireing runs that are close to large AC runs, AC Motors and lighting balast. try turning off all the power in the building if you can, execpt for the video eqipment, if you still have a loop its your equipment, if not turn the breakers on one by one at see what causes your interference loop.

 

That's not typically related to a ground loop. EMI (electro-magnetic interference) is INDUCED noise from another energy source.

 

One CAN exacerbate the other, but they're not the same cause.

 

I always have a four way Acitve receive Balun to test to signal on, most cases it seems to remove the humbar and bad video from the loop.

 

That's because the active balun inserts electronics into the path that physically breaks the ground path.

[Kiwi 0]

Perhaps there's a "luck" component too

 

I have 2 cameras at home at the front door, both cheap board cams with a common (-) and video shield, both on the same 12V power supply (over the Cat5E) and both running passive baluns.

 

The 30 yards of Cat5E runs directly alongside the 240VAC (flat cable) mains feed to my apartment for about 3 yards.

 

Despite breaking all the rules we have discussed, no problems at all, although they are monochrome so no high-freq color component.

[Soundy 1]

Yes, there's always an element of luck involved, as well as a bit of voodoo magic - sometimes you can follow all the "rules" to the letter and use only the best components,and still have problems.

 

I have a rough idea of how video baluns are wired internally, but I've never delved into the exact design or WHY they're done that way... but I do know how audio baluns and balanced lines work, and I know they're done differently.

 

In a balanced audio line, you can run right beside high-voltage, high-current AC without a problem - because of the way the balanced line works, any noise (EMI) that's induced in the line, is induced equally in both sides of the line, and gets "canceled out" when it hits the transformer at the receiving end. The transformer also provides physical isolation of the signal source from the receiving equipment, so you avoid ground loops in the signal line. A typical balanced audio also includes a shield, so the two devices are grounded to each other via that, but the signal line itself is isolated.

[Kiwi 0]

The problem with passive video baluns is that they don't isolate the two ends so you have to provide that yourself or accept the consequences. The immunity to common mode interference should be equally as good as balanced audio however, as the same principle applies. Same with all other data communications that use a balanced pair - it's certainly becoming a major player these days in computing, SATA, etc.

 

No doubt the video application is further complicated by the fact that an RS-170C (video) signal technically has a DC component, unlike most other signals.

[protech90 0]

Just to add to this subject.. we had the noisy - rolling type problem on a 4 camera (detached) building combining them to a 16channel dvr in the main building on cat-5 passive; 12vdc power supply with 4 outputs, Like everyone else if we power them one at a time or use individual 12vdc power supplies problem solved.. We ended up removing 2 or the cameras from the metal building and mounting them on the wood (non-conductive) part of the building and it cleaned up all problems.. so if isolated from the building ground has something to do with the issue as well??? what's up with that?