Sunday, December 20, 2009

On the importance of line of sight

Lesson learned:

Line of sight matters when choosing a spot for your TV antenna. A lot. TV signals don't penetrate buildings very well, so if you are living in an area with weak or difficult reception, it's incredibly important that the antenna has as much direct line of sight to the broadcast tower as possible.

A wile ago I climbed on the roof with a roof mount antenna in hand, sat down in the middle of the roof and measured reception quality using the hdhomerun_config_gui software. Reception quality was not great, but sufficient for HDTV at head height when sitting on the roof top. Since the mast that came with the antenna is only about 20 inches high, I replaced it with some bent leftover 1" EMT pipe to get the antenna to ~40 inches above the roof.

Then I mounted the antenna on one of the side eaves of the roof.

Turns out I put it on the wrong side of the house. From roughly the middle to the right-hand side of the roof, the line of sight to San Francisco's Sutro tower passes through a gap in the row of houses on the other side of the street. However, from the left hand side of my roof, there is a two story house in the way. Since Sutro tower is 50 miles away, it's not high enough to peek over the top of that house, and the signal is not strong enough to pass through my neighbor's house and make it to my antenna.

I could either mount the antenna higher above the roof, which will require a longer pipe and possibly some bracing and cross-wiring both to keep the antenna stable and to avoid overloading the antenna mount. Or I move the antenna to the right-hand side of the house ... which is what I'll try next.

As is I can receive several local independent channels, as well as PBS, but none of the other big broadcast networks.

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