The Federal Communications Commission requires all broadcast television stations to transmit digital transmissions only. To decode these transmissions you must use a digital television or have a digital-to-analog converter box connected to your TV and antenna. As for analog TVs, you must have an antenna in order to receive over-the-air channels. For information on digital television signals in your area, visit the FCC website.
Digital Television Antennas
When seeking to receive digital television signals from all stations, the only necessity is that your antenna receive both Very High Frequency channels and Ultra High Frequency waves. Even if you have a digital-to-analog converter box, an antenna is still necessary to receive the signals. Often, digital or "HDTV" antennas are advertised as receiving both VHF and UHF signals, but do not perform very well with VHF channels. Indoor antennas typically need amplification, such as an additional wire loop or bowtie antenna in order to pick up all channels.
Antennas for Different Conditions
In many areas, including metropolitan areas and nearby suburbs, over-the-air television signals are strong and may require only an indoor, TV-top antenna set-up. This usually includes rabbit ears, which receive VHF signals and an amplifier to receive UHF. Combined, this setup should offer strong channel signals, including high definition channels. In smaller cities or in suburbs a moderate distance away from the nearest metropolitan area, signal strength may be less than ideal and require a high-quality indoor antenna, or possibly an outdoor antenna. For rural areas and far away suburbs, where signals are weakest, a large, outdoor antenna is probably necessary to receive strong channel signals.
Analog vs. Digital Antennas
In truth, there is no difference between an older TV antenna and a newer "digital" antenna. A TV antenna is a TV antenna. If you received strong reception with your current antenna in the past, you will probably receive the same reception of digital channels with the same antenna. This may not be true if the range of the broadcaster's signal has changed since the switch to digital-only. It is vital to note, however, that your antenna must receive both VHF and UHF signals to receive all channels.
Many factors can affect the strength of the TV signals you receive and thus the antenna you buy. Two of the most important considerations to take into account when choosing an antenna is your distance from the transmitter, and the type of terrain between you and the transmitter. It seems reasonable that the farther a signal travels, the weaker it will be received. Also, if you are located in a valley or behind hills, it may be necessary for larger antennas or outside directional antennas. As a rule of thumb, the further you are from the transmission source, the larger your antenna needs to be, and outdoor antennas get better reception than indoor antennas.