22 Kb
The Humbug must be installed in the video cable that has come directly from the camera, but before the cable has been connected to anything else.
The shield of the coaxial cable between the Humbug and the camera must not touch any metal surfaces between the camera housing and the Humbug. (This is unlikely with a standard insulated cable.)
If several video cameras come from the same area, fix a Humbug in every cable, or a ground loop will still remain.
Picture distortion occurs in many installations. This can be caused by the following: Ground loops, mains pick up and cross talk.
Ground loops occur when the earth potential at the camera is different from the potential at the monitor. This difference may only be a small voltage but it can cause large currents to flow through the shield of the coaxial cable. The Humbug breaks this circuit only allowing video and camera control signals through. These large currents will cause picture distortion and safety problems if they remain.
Mains pick up occurs when coaxial cable runs in parallel to a power cable. A sinusoidal voltage develops on both the shield and the video core. This is often seen as a "hum bar" passing down the screen. Because the Humbug only sees the difference between signals connected to it, the video is passed without the hum.
Cross talk occurs when a cable carrying high frequency signals lies next to the video cable. This is often seen as diagonal lines passing across the screen. Sometimes they come and go, the Humbug eliminates most of these as it only sees the difference between signals connected to it.
The Humbug was developed because existing "ground loop transformers" we measured performed badly. We only found one good one, and the Humbug was better! Most transformers we measured had low bandwidth and often distorted the video image and caused loss of colour.
The Humbug is not a transformer in a box, it is an example of high quality magnetic engineering using the latest ferrite materials which allow high bandwidth and compact size to be achieved. We suggest our customers issue them to their installation and service teams to deal with problems as they occur. It is preferable to design the Humbug into each system, one per camera.
