Antennas are a Critical Factor in Successful Over-The-Air Digital TV Reception

Viewers who use an antenna to receive television programming are currently being getting bombarded with messages that they need to convert to digital in order to continue receiving TV programming after February 17, 2009. These messages discuss the need for a converter box but mention little or nothing about the antenna required.

Some viewers have already converted and are very happy about the clear digital pictures, while others are having difficulties. Viewers that used rabbit ears and got a snowy or ghosty but watchable picture on analog are finding that when they switch to digital (DTV) with a new digital TV set or an inexpensive converter box on their existing analog set, their reception is unacceptable. A proper antenna can make the difference between perfect reception and an un-watchable or absent signal.

Many viewers purchase improper antennas, misled by the declarations advertised on the box or accompanying literature proclaiming them: “Ideal for Digital TV and HDTV reception.”

Retail sales clerks usually are not very knowledgeable about the technical features of antennas and what is really needed to adequately receive digital TV broadcasts. When the purchaser hooks up their newly-purchased antenna they are often disappointed with the results.

Some viewers use a set-top antenna with a built-in amplifier thinking that will solve their reception problems. The amplifiers come in various amplification strengths labeled 20dB, 40dB, and 50dB, etc. The rabbit ears receive a poor signal that cannot be improved with an amplifier no matter how powerful the amplifier is. The best thing is to start with a good antenna that can receive a good signal. Amplifiers can be overloaded by a strong nearby signal resulting in very poor or no reception at all. Some poor quality amplifiers make reception worse.

The importance of the antenna cannot be emphasized enough. The antenna must be adequate to provide continuous reliable and flawless reception with varying signal and weather conditions.

Ordinary rabbit ear antennas are probably the worst choice for digital TV reception. Most DTV broadcasts are on the UHF frequencies, channels 14 and above. Ordinary Rabbit ears are long to receive the wavelengths of VHF channel 2 through 13 and they are TOO long for use on UHF channels providing little or no signal strength gain.

Typical Rabbit Ear Antenna

The circular ring picks up the UHF signals and the straight elements (ears) pick up the VHF channels.

Reception of digital signals can be affected by terrain and obstructions such as tall buildings. Digital receivers have difficulty receiving a reliable signal in the presence of multipath. Multipath is when the broadcast signal is reflected off of an object or multiple objects such as a water tank or any building capable of reflecting TV signals—especially land features in the mountains.

The reflected signals take a longer path than the signals coming direct from the transmitter to the TV set. This is known as multipath. Multipath manifests itself as ghosts or multiple images in the analog reception of pictures on an analog TV set. Some reflected signals can be stronger or weaker than the direct signal and the results can severely interfere with DTV reception. Multipath in the received signal of a DTV set can result in no picture at all or a picture and sound that breaks up or comes and goes.

Newer designs of digital TV receivers design have improved the capability to receive digital signals in the presence of multipath, however they are still affected by severe multipath. Reflections off stationary objects results in static multipath and reflections off of moving objects results in dynamic multipath which is even more difficult for DTV receivers to deal with.

In order to minimize multipath, the use of a directional antenna is required. An omni-directional antenna that receives signals equally well from all directions is a poor choice for DTV reception. A directional antenna usually consists of multiple elements and has to be pointed directly at the transmitting station for best results. Rabbit ears pick up signals equally as poorly from the side and cannot reject reflected signals.

Another difficulty is reduction of the broadcast signal strength by nearby tall trees. Trees can severely attenuate the DTV signals and create multipath reflections.

Some indoor antennas are designed to be directional. An example of an indoor directional antenna is the Silver Sensor antenna sold under the Zenith or Phillips brand name. Many viewers that live in a strong signal area close to the station have seen very successful results with these small indoor antennas.

UHF Indoor Silver Sensor antenna

This antenna is directional and gives good results in strong signal areas. It is small in size, about 10 inches across.

A search on the web will provide numerous mail-order companies selling this antenna. Prices range from about $20 to about $40, plus shipping charges.

Typical Directional UHF antenna for outdoor use

This is a Channel Master model 4248. This antenna is very directional, helping to reduce multipath and improve signal strength.

Channel Master Model 4221

Combination UHF / VHF / FM Antenna

Combination antennas are a compromise and work well for many viewers.

VHF TV signals cover frequencies of 54 to 213 Mhz. (Megahertz) on channels 2-14. UHF TV Channels go from 406 Mhz to 890 Mhz on channels 14-69. The small elements and reflector on the front of the antenna pick up the UHF signals.

To get the best UHF reception, a dedicated UHF antenna is recommended. In some areas all DTV stations are broadcasting on UHF channels so a dedicated UHF only antenna can be used. If you are in a strong signal area, the UHF antenna will also pick up the higher VHF channels adequately.

It is important to use a good quality coaxial cable to bring the signal from the antenna to the TV set. The length of the cable is important also. Keep the cable run as short as possible and cut off any excess cable. If the cable is too long the signal will be lost in the cable or “attenutated.” High UHF channels are attenuated more than the VHF or low UHF channels. An amplifier mounted at the antenna can be used to overcome the cable loss if you have a long run to yourTV.

It is very important to use a high quality antenna pre-amplifier. Winegard and Channel Master are examples of good pre-amplifiers.

How do you know what antenna to choose and how strong the DTV signals are at your residence? You can call the station you are interested in receiving and talk to their technical staff and ask them to give you the information you need or ask them to recommend an antenna. UNC-TV will do a computer signal analysis of our predicted signal level at a precise location for viewers that request it or they can determine this information by using resources on the web.

Safety and proper installation are very important. Watch out for overhead electrical wires when installing an outdoor antenna. Follow good installation practices, including proper grounding of the antenna and downlead cable.

Recommended online resources:

Antennaweb
This informative site is provided by the Consumer Electronics Association and provides information about the stations you can expect to receive based on your location and what direction to point your antenna.

AV Science Forum
Home electronics discussion forum.

HDTV Primer
What you need to know when buying your first high definiton television.

HDTV Primer: Erecting a TV Antenna
HDTV Primer information on installing a home antennna.

TV Fool
Home for more signal analysis tools.

Antenna Manufacturer Web sites:

Antenna Craft

Channel Master

Winegard

Information provided by:

Wayne Estabrooks, Former Chief Engineer (Retired), UNC-TV