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Earthing for TV
distribution system

We recently had a room added to the house which then required a TV outlet. This and the purchase of an HD LCD TV prompted me to replace the motley collection of cable and splitters in my distribution system, which over the years had grown from the original single point to five. I rewired in RG6 cable with F connectors and cast alloy splitters. The improvement in reception is amazing.

One of the old splitters had failed on one output and the 5-year old Akai TV in that room had used a “rabbits ears” antenna. When I connected this to the new system, we had 50Hz hum on all radios in the house. When I unplugged the fly lead from the wall socket I felt a tingle when I touched the shroud.

I measured the voltage to earth with my Fluke DMM and it was 110VAC. As it could supply no current, the source was obviously high impedance. I have not had time the look at the TV yet to find the cause but it made me think about the lack of any earthing on the antenna system.

In the days before live chassis, switchmode supplies and 2-pin mains plugs, the shield on the antenna cable was earthed by its connection to the earthed chassis. Now the whole system floats above earth so that if a fault connects it to a dangerous voltage, there is no path to cause a protective device, fuse, circuit breaker etc, to operate.

I am planning to connect the metal housing of one of the splitters to my house protective earth, so as to provide this path.

Phil Andrews,
Adelaide, SA.

Comment: you would be better off earthing the whole system where the cable connects to the antenna. Earth the antenna as well. A separate grounding stake is desirable. This will also improve noise immunity on digital TV reception.

Possible flaw in
GPS-Synchronised Clock

With regard to the GPS-Synchronised Clock in the March 2009 issue, surely the fatal flaw is that the GPS receiver won’t be able to pick up satellites anywhere indoors. My relatively modern GPS receivers (a Garmin hand-held and Garmin car unit) don’t have a hope of getting satellite signal anywhere in my house where I would want a clock. Am I missing something?

Mark Stephens,
Brisbane, Qld.

Comment: the recommended EM-408 GPS module is extremely sensitive. It works fine in our building which has a steel roof. Even better, it continues to work when placed in a steel filing cabinet!

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