Digital TV antenna orientation

by Matthew Gast


Last September, I started getting my TV from digital broadcasts (as described in an article at the time). One of the consistent problems since then is that channel 2-1 has consistent audio drop-outs, often coupled with severe pixellation or total loss of the video. The problem seemed to be worse at night.




In the course of fiddling with the antenna, I noticed that if the antenna were pointed up slightly, the signal from channel 2-1 was significantly more stable. I placed a TV Guide under the front of the antenna to tilt it slightly up. There's a hill between Sutro Tower and my location, so it's not surprising I got slightly better results by pointing the antenna up slightly towards the crest of the hill.




Even with the slight tilt, the signal still dropped out a few times per hour. With some more experimentation, I discovered that if the antenna elements were vertical, rather than horizontal, channel 2-1 was flawless.




Improving the picture by turning the antenna vertical was a bit of a surprise for me. Antenna elements should line up with the polarization of the broadcast signal. Most TV stations in the U.S. transmit with horizontal polarization. (As far as I can tell, this is a historical tactic used to avoid interference, since most human-caused electromagnetic noise has vertical polarization). In fact, the FCC records for the station show that the digital signal is transmitted with horizontal polarization. Perhaps there is something about my particular geographic location or construction of the dwelling that causes vertical polarization.




If I moved the antenna to a vertical orientation, however, I lost all the other stations (4, 5, 7, 20, and 44) from the same tower. Fortunately, electromagnetic waves are vectors. By tilting the antenna to one side, I could get a combination of both the vertical and horizontal signals, and get all the channels without signal dropouts.




In the end, I wound up propping up one side to get the antenna orientation I wanted. It now points slightly up towards the transmission tower, and is tilted to one side. All the local channels off the transmission tower have been rock-solid since I made the change a week ago.


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3 Comments

Gene1206
2005-02-06 12:02:13
Pixilation
Do you have any experience with consistent signal interruption problems when using a large rooftop antenna, new coaxial cable, and a signal booster. My signal comes into a Samsung HDTV tuner box and I have a Sony 30" Wega XBR CRT TV set. I am only about 20 miles from towers, and have several strong local stations, but my house is in a bit of a valley with some semi-tall office buildings nearby in more or lesss the direction of the towers.
mgast
2005-02-07 08:32:51
Pixilation
Gene,


A couple of questions for you:


1. Which Samsung tuner do you have? There are several generations of chipset on the market, and they perform differently.


2. I assume you're using RG-6 cable, which is much lower loss than RG-59.


3. I assume the preamp ("signal booster") is mast mounted up near the antenna. Which model is it?


4. You may get better results by fiddling slightly with the height; see the HDTV Primer antenna siting guide.

reciprocate27504
2005-02-09 06:23:13
Pixilation
In response to tilting your SilverSensor HDTV antenna I have one of these just by accident I laid it down on its back. Unbelievable I was able to receive channels clearer than in a horizontal standing Even some Vhf channels were sufficient