The purpose of this Guide is to provide information for improving UHF television reception in the home. The installation techniques below have been proven with our customer's installations over the past ten years. If followed, you should have a high quality installation that will deliver good TV reception for many years.
History and Future of UHF TV
Before television first began, the Federal Communications Commission allocated twelve channels for television broadcasting. These channels, 2 through 13, are in the "very high frequency" or VHF band. (Originally Channel 1 was also included, but was soon reassigned to other purposes.) The tremendous growth in television broadcasting following World War II made it obvious that 12 channels were not enough. So in 1952, the FCC allocated 70 additional channels above the VHF television band and called them "ultra high frequency" or the UHF band. These were channels 14 through 83. Then in the early 1980's, channels 70-83 were reassigned and became cellular telephone frequencies. By the year 2010, channels 52 through 69 will be reassigned to uses other than TV broadcasting, due to the rapid growth in portable communication services. The UHF band will not lose 18 TV channels though. These TV channels will be incorporated into the new high definition television (H.D.T.V.) broadcasting standard, which can broadcast up to six digital channels in the same space as one analog channel. Using high definition television, TV stations will be able to broadcast a picture quality that is twice as sharp as the analog broadcasts of the past. Digital broadcasting will also allow adjacent channel spacing of TV channels without creating interference between the two channels, making the broadcasting spectrum more efficient. To see what TV stations in your area are currently broadcasting a digital signal.
UHF Reception
UHF signals, due to the physics of radio frequency transmission, are inherently less efficient in the conversion of radio waves to the electrical signals used by the television receiver, and are subject to more losses from some environmental conditions than VHF signals. Good UHF TV reception therefore requires more attention to antenna installation and tuning (on older TV's and VCR's) compared to VHF TV reception. On the other hand, some VHF channels are subject to certain types of interference to which UHF channels are generally immune.Perfect reception for television signals can't be guaranteed simply because there are too many variables involved. However, by following the recommendations in this guide, the chances for clear reception will be greatly improved.Improving UHF reception can be a do-it-yourself job. Even if the work is given to a professional, the information in this guide will provide a better understanding of what is needed and what can be expected.
Poor Reception and Poor Antennas
If UHF reception in general is bad, how it's bad can help determine the problem. "Snow" is visual noise caused by a weak signal, poor antenna system, the set itself, or a combination of these. "Ghosts" or multiple images are caused by a signal arriving from two or more directions simultaneously reflected off buildings, trees and hills. A good antenna system often solves these reception problems. An outdoor antenna is better than an indoor antenna, and an indoor antenna is better than no antenna at all. If an outdoor antenna is needed for good VHF reception, you'll almost certainly need an outdoor antenna for good UHF reception. But if good VHF reception can be obtained with an indoor antenna, a bowtie or other UHF antenna on the TV may also work. Indoor antennas:All indoor antennas can be adversely affected by the walls of a house, inadequate height, and by movement of people in the room-as may be noticed with VHF "rabbit ears". Loop or single bow tie UHF antennas are usually not satisfactory. They are difficult to adjust for maximum signal pick up or for elimination of ghosts. Most indoor combination VHF/UHF antennas have a multi-position switch that can be adjusted to help get the best picture quality and some even have a built-in amplifier. As a rule, these antennas are not good for UHF. Most portable TV's have a VHF/UHF telescoping rod antenna, or "monopole", and normally UHF reception is poor with it, but can be enhanced when the antenna is shortened to a length of 7 to 12 inches. The best indoor antennaIf an indoor UHF antenna must be used, the Radio Shack model 15-623 double bowtie with reflector screen (pictured) is the best choice. But, keep in mind that nearly all outdoor antennas are always better than even the best indoor antennas. Make sure the antenna wires are connected to the UHF terminals on the back of the TV and/or VCR.
Outdoor Antennas
There are many different types of outdoor antennas available in a wide price range. The type selected is determined primarily by the geographic location of the receiving TV.4-bay bowtie UHF TV antenna (8-13dB gain) for suburban to fringe reception areas with medium signal.
Television signals are strongest when the TV station's broadcasting antenna and the home receiving antenna are in line-of-sight. If the line-of-sight is blocked or weakened by hills, buildings or trees, the signal, likewise will be weakened or lost. The signal will also get weaker as it travels farther from the broadcast antenna. "Gain" is the measure of an antenna's sensitivity-- and its ability to pick up signals. It is measured in decibels (dB). As you move farther away from the TV stations broadcasting antennas, the size of the TV antenna that you will need will increase. Lower quality antennas that claim to be for fringe reception areas often have a long boom, but do not have as many elements as higher quality antennas do. These elements are the actual part of the antenna that capture the incoming signal. The more elements that an antenna has, the more gain it will have, and the more signal it can receive.Gain can also vary from channel to channel on the same antenna and it can also vary between different antennas. For example, an antenna's gain at Channel 14 may be 8dB, but the gain at channel 69 may be 13dB. These are just a few reasons why it is very important to compare antenna specifications and get the right antenna for the area that you live in.Where buildings or other obstructions cause "ghosts", an antenna with good directivity is recommended. Directivity is the ability to receive only those signals at which an antenna is pointed. Highly directive antennas have narrow receiving angles (measured in degrees) and high "front to back ratios". These ratios represent the antennas ability to receive signals from the front of the antenna compared to receiving the same signals from the back of the antenna. The higher the front-to-back ratio is on an antenna, the more it will try to reject any unwanted signals from the rear of the antenna. This is especially helpful in areas where adjacent channel interference is a problem or where there are two channels on the same frequency and only one channel is desired. This is called "co-channel interference".If already have good TV reception on the VHF channels, it will probably be less expensive to add a good quality UHF antenna on the same mounting mast. The separate UHF antenna also will permit pointing to VHF and UHF TV stations which may have their broadcast antennas in different directions from your location. If all television signals are coming from the same direction, both VHF and UHF reception can be improved. Choose an antenna according to the distance to the most distant UHF station for which reception is desired by installing an "all-channel" combination antenna. This is the most common type of outdoor TV antenna. There are several good quality "all channel" VHF/UHF TV antennas available. If the UHF stations to be received are located in different directions from your house (more than 30 degrees apart):
· Either use an antenna rotator
· Or combine two antennas together using either a mast mounted combiner or a backwards 2-way splitter.
