Have you ever been watching television when, suddenly, horizontal bars appear and slowly start rolling up your screen? Sometimes they are merely a shadow that minimally distorts your picture. Other times, it is a black bar that completely blocks out a small portion of the picture as it rolls along.
Well, if you have frustrated yourself by trying to adjust the horizontal hold on your TV set and not seeing any improvement, its likely the problem is caused by an electrical current abnormality. These types of bars are known as 60Hz bars and are caused by an electrical abberation called ground loop. CCTV installers also come across this problem more often than they’d like.
While the occurrence of 60Hz bars is simple to detect, often it is much more difficult to locate the source of the error. It’s always best to design a new installation to ensure against ground looping.
However, whether it’s on a new install where you want to ensure that ground loop doesn’t happen or on a service call where the problem already exists, there are some simple solutions.
Ground Loop Causes 60Hz Bars
When video ground loop problems occur, a 60Hz bar will appear on your video monitor. Often, these bars can be barely noticeable. Sometimes, though, they can be so bad that the monitor loses its lock, and the bars break up the picture.
Simple Solutions Make Installs More Precise
The simple solution to ground loop and 60Hz bars is to never connect both ends of a video cable to local grounds. Any cable can be grounded at one end without inducing the ground loop current. When you run coax cable from one building to another, it is acceptable to install it through connection points. However, do not allow the shields to come into contact with one another or the local ground.
Pre-Existing Problems May Have Many Causes
If you already have an installation that has 60Hz bars, there are some steps you can take to solve the problem. If coaxial cable shields are connected together anywhere in the system, separate them if possible. Similarly, remove all but one ground connection on each coax if possible. The ground should usually be at the monitor end of the coax, because the monitor equipment plugs into the 60Hz main power supply, which is grounded.