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Hum Irony

451 Views 1 Reply 2 Participants Last post by DMF, Feb 23, 2005

Matt_Doug

Discussion Starter · Feb 21, 2005

Grounding the cable or satellite feed at the house ground (as required by NEC) has been touted here as a solution to ground loop. According to this link:
http://www.broadband-pbimedia.com/ct...99/ct0599d.htm It maybe the cause. here's the summary:
Quote:

...the cable shielding, and consequently also the splitter housing, is bonded to the buildingâ€™s "grounding electrode" as specified by the National Electrical Code (NEC) or other requirements? The shield and splitter housing are placed at the same ground potential as the buildingâ€™s electrical power neutral conductor.

This is done to minimize potential differences between cable and power grounds. It also means that power company or in-house neutral fault currents will be shared between the neutral conductor and cable shield.

Neutral fault currents that exist on the outer surface of cable shielding can enter a subscriberâ€™s drop wiring via the toroidal transformers found in drop splitters.

This will, under some circumstances, cause an electrical current to flow on the cableâ€™s center conductor. If the electrical current is large enough, it will saturate the splitterâ€™s toroidal transformer ferrite core and cause hum modulation.

The initial fix was to install a voltage blocking coupler (VBC) on the splitterâ€™s input port, which prevented the unwanted electrical current from flowing in the drop. This success led to the use of drop splitters with built-in blocking capacitors on all of the splitter ports, a low-cost and effective fix to this potentially serious problem.

So if you're cable is properly grounded and you're still experiencing significant hum, make sure your slitters are equipped with blocking or "port protection" caps. This article is 5 + years old, So maybe its not an issue now - but you never know.

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