At the writing of this article February 17, 2009 is the projected date when all television stations in the United States of America will switch to digital television (DTV). Anytime a new technology becomes available to the general public there are those who will try to take advantage of people who do not have the technical knowledge to discern fraud from fact. These shysters try to sell people products they claim will give improved performance when, in fact, their product is no better than something else that is on the market for a much lower price or these products may do nothing at all. There are some of these so called improvements that even cause damage to existing equipment when used.

Do you remember the TV advertisements for the little stick-on device designed to go on the back of a cell phone with the promise it would improve the performance of the phone? To prove it worked one ad showed a lady holding two cell phones in an elevator. The phone with their product worked but the other did not. These worthless stick-on gadgets must have sold like hotcakes because while I was working as a technician for a major cell phone company I saw hundreds of them but they did not change the operation of the phone not even a little.

Similar things are surely to be made available to enhance your DTV experience and I predict, based on experience not prophecy, that DTV antennas will be the number one scam. A little knowledge about antennas and how they work may save you some money and grief.

This is not meant to be a full antenna course. Antenna, though they look simple, can be very complex in their operation.

A receiving antenna works by changing the electromagnetic signals (radio waves) broadcast from a transmitting station into radio frequency alternating current which is conducted to the input of the television via a feed line (twin lead, ladder line, or coax). (That may sound deep but hang in there for just a little bit and it should become clearer.)

Radio waves (Television signals are sent on radio waves) are similar to sound waves. The two big differences in sound waves and radio waves are: one, sound waves are mechanical vibrations while radio waves are electromagnetic vibrations. That is why sound travels a little over 330 meters per second while radio waves travel approximately 300 million meters per second. The second major difference between the two wave forms is sound waves are lower in frequency than radio waves (that means sound vibrate slower.)

You may have experienced a tuning fork after it has been started vibrating and giving off a tone (frequency) start another tuning fork of the same frequency to vibrate when it is brought near the first tuning fork. The second fork vibration is caused by a process known as "sympathetic vibration." The vibrations of the tuning forks are mechanical vibrations which cause the sound to be produced by compressing and decompressing the air molecules. The air molecules vibrate mechanically (physically) in waves from the tuning forks

An antenna produces sympathetic vibration electrically when in the presence of an electromagnetic wave (an electromagnetic wave is an energy wave). The frequency of a tuning fork is determined by its physical construction, mostly the length and thickness of the forks. This operating frequency is known as the resonant frequency. An antenna also has a resonant frequency which is determined by its physical construction, length being the most dominant factor.

The antenna is an extremely important piece of equipment because it is antenna that connects the television receiver to the transmitting station's signal. If the antenna is designed to be resonate at the transmitting station's operating frequency it will operate much more effectively than it will if it is not resonant. A resonant antenna will deliver more energy to the TV set than a non-resonant antenna. The old saying "the bigger the antenna the better it will work" is not necessarily true.

An analogue television broadcast consists of a picture which is amplitude modulated (AM) and audio which is frequency modulated (FM). If you don't understand the difference between AM and FM it doesn't matter they are just two different formats used to place the television picture and audio on the radio signal. With DTV all the information is sent digitally. As far as the antenna's operation is concerned it doesn't matter whether the signal is AM, FM, or digital. All that really matters is the channel frequency is the same as the antenna's resonant frequency.

Before the switch to DTV television channels 2 to 13 were transmitted on Very High Frequencies (VHF - 30 to 300 MHz). All the other channels were transmitted on Ultra High Frequencies (UHF - above 300 MHz). The new DTV channels will all be on UHF so if a television set is connected to an antenna that has a UHF antenna, whether or not it is combined with a VHF antenna, the antenna should work fine on DTV by using the UHF portion of the antenna whether it is connected to a new DTV or to a converter box.

DTV does not have "snow," "ghosts" (double images), or a wavy picture. It also does not have static in the sound. For the most part it is either in or it is out. This means to consistently receive a DTV station an antenna upgrade may be necessary if the current antenna system is strictly for VHF (there are not many of those around anymore) or if an indoor "rabbit ears" antenna is being used.

The rabbit ears antennas are subject to several problems. First the long adjustable ears of the antenna are for VHF and the UHF portion can not normally be changed with frequency changes which occur when the channels are changed. To accommodate the various channel frequencies a quality antenna must be wide band. The process of making an antenna wide band is far beyond the scope of this article but any antenna that claims to receive all the UHF or DTV channels will have several elements (the rod or wire that picks up the signal) of varying lengths. Small wideband indoor antennas are available for reasonable prices.

Another problem with indoor antennas is the loss of signals due to something or someone moving in the room with the antenna and sometimes even in other rooms near the antenna. This movement may be people or pets walking around in the room. These moving bodies can change the pattern of the signals in the room because of their reflection and absorption of the signal. A simple directional indoor antenna may reduce this problem and in the right conditions perform satisfactorily. Fancy indoor antennas with lots of loops, spikes, and gadgets are probably not going to help just like those silly stick on things used on cell phones didn't help.

Radio waves do not see color so it does not make any difference what color a TV antenna is. In the 1960's a company was selling a black and white TV antenna made of bare aluminum for a price and they were selling the exact same antenna with gold color coating they said was for color TV at more then double the price of the other antenna. The gold coloring was not gold and cost almost nothing to put on.

Most outside TV antennas are directional and thus need a rotor if they are used to receive signals from various transmitters in different directions from the antenna's location.

If an outside antenna is already in use and has been in use for several years it might help to replace the feed line. Feed line deteriorates from weathering and the line loss which is not be noticed at VHF frequencies may not work well at UHF frequencies.

If you still need help with your installation talk to a professional you can trust. Stick with the conventional antenna systems and stay away from hyped gimmicks.