OTA HDTV Reception Q&A

Updates on the DTV transition and how to receive over-the-air digital television for free.

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Location: Richmond, IL, United States

Hello there! I created this blog to share the information about over-the-air HDTV reception you have been wearily searching the Web or calling technical lines for, whether you have decided for less expensive means to get your favorite TV shows, or still adjusting from the over the air broadcast DTV transition that occurred on June 12, 2009. After working for a leading antenna manufacturer for almost 5 years, during which time I've shared my expertise with those who asked on the phone and by email at work, I decided to do the same in the Blogosphere! Confused about getting your local HD channels? Just click through the archives, some of the most useful information is in the early posts from 2005-06. If you want to get in touch with me with antenna related questions, just leave a comment anywhere on this site.

Sunday, November 06, 2005

SO I GOT AN OUTDOOR ANTENNA, WHERE SHOULD I PUT IT?

This week I wish to share a couple tips on how to position an outdoor antenna. For DTV reception, positioning the antenna is very critical, as I mentioned in my first post, available for viewing in the archives. Not only could lack of signal break up a DTV picture, but also anything that would cause visible interference on an analog TV picture, which cannot be seen on a digital picture. Unfortunately, when a DTV picture breaks up, it is too easy for the average consumer to assume that there is a lack of off-air signal causing this, so that consumer gets an amplifier only to find that the so-called "digital signal strength" has either not improved at all, or got even worse.

So if there is a problem with the signal, before you spend money on an amp from a place with a strict return policy (or lack thereof), check for these little pitfalls. If the antenna is inside an attic, some of these issues could apply as well.

1) Is there anything metallic in the presence of the antenna? If there is metal, even meshed metal, in front of the antenna, then the metal is blocking the signal, leaving not much for the antenna to collect. Also, if there is sheet metal within five feet or less below the antenna, then the metal is either loading some received signal, or reflecting some signal, which would result in "multipath", a condition where undesired reflected signals are being collected in addition to the line-of-sight signal, resulting in ghosts in analog pictures, or reduction of the DTV signal.

2) Are there any obstructions to the line-of-sight, such as trees, tall buildings, or hills? These items may block signal collected by the antenna. Heavily wooded areas may require a stronger antenna to pull i off-air signals. In other cases, you may want to get a little open-minded and try pointing the antenna off the line-of-sight and aim it at a tall metal structure that is visible, like a water tower, cell tower, or skyscraper with a metallic frame. Here multipath may actually become BENEFICIAL since there is more multipath signal and little line-of-sight. A directional antenna would be very helpful in such cases; "directional" being an antenna with at least 10 dB front-to-back ratio on the channel you are trying to receive. In addition, the curvature of the earth between your area and the transmit towers may also result in having you turn the antenna off the line-of-sight angle only to find more signal! You can determine the line-of-sight angle for your area by visiting http://www.antennaweb.org/ or http://www.checkhd.com/ (locate the "Antenna Guide" link after entering in your location information).

3) You might also find that raising or lowering the antenna by at little as a foot could shoot up the digital strength meter on difficult channels. It is possible that by doing this an undesired signal interfering with the digital signal will miss the antenna, improving the integrity of the digital signal being sent to the tuner. In "fringe" areas, at least 50 miles from the transmit towers, the signals start having strong points and nulls as the field strength becomes weak. So, raising or lowering the antenna a foot could allow reception of a stronger signal where a null otherwise would be.

4) If after doing all that, the amplifier should be put into place, and if there is no change, then maybe you might want to find someone with an RF field meter to actually see the digital signals received by the antenna. Seeing the signals will allow you to see if there is an interfering analog signal either causing a "spike" or a "valley" in the response, which would complicate the ability for the tuner to decode the signal. If you are a professional installer, I would strongly recommend you get such a meter. Good manufacturers are Sadelco (http://www.sadelco.com/) and Sencore (http://www.sencore.com/); Sadelco offers more affordable solutions.

Other little tricks is to check the cable; there may be a break in it inside that you can't notice. If you have an amplifier with a plug-in transformer that sends voltage up the cable line, hook one end of the cable to the transformer, plug in the transformer, and then check the other end of the cable with a voltmeter. The red lead would touch the center conductor/wire of the cable, and the black lead on the nut. If ample voltage is read by the meter, the cable is okay; if there is low reading, there may be a break or short in the cable, and should be replaced. Also, if the cable run is going to be close to electrical wiring or conduit, quad-shielded RG-6 cable should be used to contain the signal in the cable without the electrical wires introducing interfering noise in the signal.

Last but not least, CHECK THE INSTRUCTIONS OF THE ANTENNA, INCLUDING THE SAFETY WARNINGS. The antenna should be grounded and free from power and phone lines. Not only do such items introduce unwanted noise into the signal, it could introudce a hazardous condition. If you do not understand the warnings or need information, you could check with an electrician or your municipal government office dealing with electrical or building codes.

If you are planning to get an HD tuner, do some research to see if it has a 4th or 5th generation ATSC/8VSB chipset. These tuners are more capable of decoding off-air digital signals affected by multipath than earlier DTV tuners, which would allow a little more leeway in positioning an antenna. These tuners have also made it easier to use an indoor antenna to receive off-air DTV -- there could be several sources of blockage or multipath in your living room area.

Hopefully these little recommendations will help improve your off-air DTV reception a lot faster than spending time or money and getting you nowhere. Also if you are ordering an antenna and an external preamp or inline signal booster, position the antenna first, and add the booster later. That way you can use the tuner's so-called digital strength meter to optimize the antenna position for the best signals, and then you give the best possible signals collected by the antenna the boost needed to get you the most consistent DTV/HDTV experience. Again, go back to my first and earliest post for more details, with pictures, on how DTV signals work.

1 Comments:

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2:48 PM  

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