Choosing & Installing an HD Antenna part 2
TV antenna basics
There is no one magic antenna or antenna type that will deliver excellent TV reception in every location. The main factors determining reception are the distance and direction from the TV station transmitters to your home. Other factors include the transmitter's power and the height of its tower, the terrain between the tower and your antenna, and the size and location of any large buildings in the path of the transmission.
If you live within a few miles of the transmitter, and the signal path is relatively unobstructed, you may be able to get adequate reception using a small set-top indoor antenna. But as you move farther away, getting usable signal strength becomes trickier. This is where careful antenna selection and installation become essential.
The information below will help you zero in on the type(s) of antenna that should work best for you. Keep in mind that even in the same neighborhood reception conditions often vary from house to house. For that reason, it's best to purchase your antenna from a dealer who offers no-hassle returns with a money-back guarantee.
VHF and UHFLike analog signals, digital TV signals can be broadcast over two different frequency ranges: VHF (Very High Frequency) and UHF (Ultra High Frequency). The VHF channel range is 2-13, while the UHF range is 14-83. Over 90% of digital stations currently broadcasting are in the UHF frequency band, meaning you can receive them with a UHF antenna. If some of the local stations you want to receive are below 14, especially in the 2-6 range, you may need a VHF/UHF antenna.
This can be trickier than it sounds because the FCC requires digital stations to embed a "reference" to their analog channel so viewers won't have to memorize a whole new set of channel numbers. So, your TV might identify a digital station as being in the VHF range when it's actually in the UHF range. For example, Richmond's CBS station is known as "Channel 6," but its true digital channel is 25.
What is the difference between UHF and VHF antennas? Mainly size. Antenna elements are based on the size of the waves they're designed to receive, and VHF frequencies are lower so the waves are longer, requiring a larger antenna surface to receive them. It's possible to build a much more elaborate UHF antenna with more elements for stronger reception while keeping the antenna size physically manageable.
Uni-directional vs. multi-directional TV antennasAntennas described as "uni-directional" or sometimes just "directional" are designed to receive signals from one direction. "Multi-directional" or "omni-directional" antennas are able to receive signals from all directions.
The illustration on the left shows the typical narrow, focused reception pattern of a uni-directional antenna; the pattern on the right shows the broader pattern of a multi-directional antenna. Images from hdtvprimer.com
Directional antennas are able to pull in signals from greater distances, and because they "see" in only one direction they are resistant to noise and "multipath distortion" (a problem created when an antenna receives reflections of the desired signal). Because multi-directional antennas "see" in many directions they are more likely to pick up noise, interference, and multipath distortion.
If you used the tools on the previous page to locate your desired stations, you should have an accurate picture of their direction in relation to your home. If all of those stations are transmitting from an area covering a range of 20 or less, you can probably receive them using a uni-directional antenna. If the transmitters are positioned more than 20 apart, try a multi-directional antenna. As an alternative to a multi-directional antenna, you might consider combining a uni-directional antenna with a "rotor," which lets you remotely rotate the antenna to pick up stations in multiple directions.
Indoor vs. outdoor antennas
Two antennas from Terk. On the left is the HDTVi indoor antenna, with compact receiving elements that are under 12 inches long. On the right is the outdoor roof-mount TV36, which has 33 elements and measures over 8 feet long.
Indoor antennas are generally small, designed to be placed on or near your TV. Outdoor antennas tend to be significantly larger and are intended for roof- or attic-mounting. In general, the larger an antenna's surface area is, the stronger the signal it will provide. The relative strength of the signal an antenna can deliver to a tuner is referred to as "gain" and is measured in decibels (dB). The higher the dB rating, the greater the gain.
Nearly all outdoor antennas perform better than even the best indoor antennas. Along with their size disadvantage, indoor antennas have a height disadvantage, and are adversely affected by the walls of a house and even by movement of people in the room. Other sources of household interference include fluorescent lights, computers and cordless phones.
Amplified vs. non-amplified antennasOne way to help antennas overcome size or height disadvantages, or otherwise enhance signal gain, is through the use of electronic amplification. The amplifier can be built in as it is in many indoor antennas, or it can be a separate device that installs in-line between the antenna and TV. An amplifier that installs on an outdoor antenna or mast is often called a preamplifier or "preamp." Most experts recommend only using an amplifier if you need to. The potential drawbacks of amplifiers are that they amplify noise along with the signal, and they can be overdriven by strong signals, which can make reception worse.
Other good antenna info resources
If you know of any neighbors who are using an antenna, find out what type/model it is and how well it performs. You could also try calling local TV stations with your antenna questions. It's definitely in their interest to help their viewers improve reception.
Another excellent source for info on digital TV reception is the AVS Forum's local HDTV message boards, which are loaded with great suggestions and solutions to particular reception problems in locations ranging from big cities to small towns and rural communities.
Finally, the Antennaweb site mentioned on page 1 also has wealth of general antenna info in its antenna FAQ.
Whether you're considering installing an antenna yourself or having one professionally installed, the next page offers basic tips on roof- and attic-mounting, and cabling.