Why does live video from analog cameras sometimes display scrolling black bands on the monitor?

Issue

Why does live video from analog cameras sometimes display scrolling black bands on the monitor?

Product Line

Pelco Cameras

Environment

  • Spectra IV SE / SL
  • Camclosure 2 IS20/IS21/IS50/IS51 Series
  • Spectra Mini
  • Esprit SE
  • C20 Series

Cause

Black bands scrolling on the video image could be the result of a ground loop or voltage radiation into the video caused by circuit malfunction.

Resolution

Order Pelco part number GIT100 (Ground Loop Isolation Transformer) to reduce interference with CCTV signals caused by ground loop potentials. 

A ground loop is an electrical problem that happens when an AC current interferes with the ground reference level of the video signal. It occurs on the conductive path formed by the shield of the coaxial video cable and the chassis of the video equipment. A ground loop results from the difference between the voltage potential of the shield at one end of the cable, versus the voltage potential of the shield at the other end.

The electrical level of the shield is usually zero volts. When a ground loop is present, this level fluctuates above and below zero volts. The greater the difference, the more severe the video distortion or tearing. If the potential is too great, it can destroy the equipment.

Verify video at the source; if the issue is apparent repair or replace device.