Most antenna's are directional and must be pointed in the signal direction for best reception. Antenna's can pickup signals from all directions, but signals out of the main beam are greatly reduced compared to signals in the main beam.
Indoor antennas may be sufficient for receiving full power broadcast less than about 20 or 25 miles away, if there is a relatively clear line-of-sight. Attic mounted antennas will have greater range, but there is at least a 3 dB loss compared to outside antennas. Outside antennas work the best, but are more difficult to install and should be properly grounded for best reception and safety (see Installation). A preamp mounted on or close to an indoor or outdoor antenna will extend range in most cases (see Amplifiers).
Antenna size is proportional to wavelength. UHF antennas are smaller than VHF antennas because UHF wavelengths are shorter. UHF wavelengths vary from 1 to 2 feet, VHF varies from 5 to 17 feet. A VHF/UHF antenna is actually 2 separate antennas built into one. The smaller UHF elements are built-in or around the larger VHF elements, and the UHF and VHF signals are internally combined then routed to the connector. Additionally, VHF gain is typically less than UHF gain.
ANTENNA BANDS (VHF / UHF)
Television antennas are designed to receive up to 3 frequency bands; VHF-Lo, VHF-Hi, and UHF. Most stations are in the UHF band, and most areas have at least one VHF station. Antennas on the market are available in 4 common configurations.
|VHF-Lo||2 - 6||54 - 88|
|VHF-Hi||7 - 13||174 - 216|
|UHF||14 - 69||470 - 806|
|VHF||RF 2 - 13|
|UHF||none||none||RF 14 - 69|
|VHF-Hi / UHF||RF 7 - 69|
|VHF / UHF||RF 2 - 69|
VHF and VHF/UHF antennas will also pickup FM radio (just above RF 6), aircraft voice (AM), amateur radio, police, fire, ambulance, business, public services.Also see TV broadcast Frequency.
ANTENNA GAIN AND BEAMThe larger the antenna the more signal captured and;
Gains vary with antenna and frequency from around 2 to 15 dBi (0 to 13 dBD). Range doubles for a 6 dB gain increase.
|Indoor||2 - 4||20 - 25|
|Attic / Outdoor||5 - 10||30 - 45|
|Outdoor||11 - 15||50 - 85+|
Antenna gain is measured in dBi or dBD. Manufacturer's use a standard dipole antenna to measure gain in dBD. The dBi unit is used for calculations. Be suspicious of antenna gain expressed in "dB", this can mean anything. Also see Reception / Antenna Gain Calculator to estimate gain needed.
|dBi||-||decibels (dB's) compared to a lossless isotropic radiator.|
|dBD||-||dB's compared to a standard half wave dipole antenna with a gain of +2.15 dBi.|
Antenna beam width varies from less than 30° for a high gain antenna, to 120° for some indoor antenna. At the beam edge gain is down by - 3 dB, and drops rapidly past the edge. Also see Reception Factors / Beam Loss.
Stick antennas mount directly to the television connector and are mostly out of sight, but coverage is limited. Table top antennas are easy to place and angle for best reception. Thin flat antennas can be used as a table top or mounted on a window or wall for better reception. Gain is proportional to physical area (square inches), and varies from about 2 to 4 dBi without a preamp. Many indoor antenna's are designed to make it easy to install, or uninstall, an optional preamp.
Published antenna ranges are based on a Full Power station, 1000 kW for UHF and 185 kW for VHF signals. Antenna gain can roughly be approximated from range.
Distant and spread out broadcast headings may require;
Omni antennas require a preamp to compensate for low gain (wide beam). A rotor system has the advantage of good gain and full 360° coverage. A high gain antenna with a built-in preamp mounted on a rotor has the highest performance.
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