Your home location and your antenna size and placement are the main factors that determine which broadcast you can receive. An indoor antenna works when broadcast towers are within 15 to 25 miles. An outside antenna can get signals from 45 miles or more. The larger the antenna the more signal captured and the greater the antenna gain (range). As gain increases beamwidth narrows. An antenna preamp can increase effective gain. Preamps are low noise amplifiers designed to pull in weak signals. A preamp can be added to any antenna, some antennas have a built-in or a detachable preamp.
DIGITAL vs ANALOG ANTENNAS
There is no difference between a digital antenna and an analog antenna, except the name. Digital and analog TV signals both use the same carrier frequencies. Carrier modulation (digital or analog) does not effect antenna reception.
Television stations broadcast in either the VHF or UHF Frequency Band. Most stations are in the UHF band, and most areas have at least 1 VHF station. All home antennas get UHF channels, some also get VHF channels. Some indoor antennas do not get the VHF-Lo band (RF channels 2 - 6). It's not uncommon for an antenna to get signals outside it's frequency range. The signal strength is reduced, but may be strong enough to receive.
|UHF||14 - 69||470-806 MHz|
|VHF-Hi / UHF||7 - 69|| 174-216 MHz
|VHF / UHF||2 - 69||
VHF antennas are larger than UHF antennas because the wavelengths are longer (lower frequencies). A VHF/UHF antenna combines a VHF and UHF antenna into a single configuration. A built-in coupler is used to combine VHF and UHF signals to the antenna output connection.
Also see TV broadcast Frequency.
Indoor antennas are low to moderate gain, and come in a variety of styles. Symmetrical antennas (look the same from the front and back) have identical reception areas in the front and back.
2 to 4 dBi
20 - 25 Miles
Flat Thin Rectangular Antenna
- Efficient, Light Weight
- Size: ≈ 4x4x1 to 12x12x1 inches
- Mount: Stand, Wall, Window
Table Top Antenna
- Variety of Styles
- Some use Rabbit Ears for VHF,
- Some use a Loop for UHF
Many indoor antennas have detachable preamps, some are built-in. The preamps are powered by house current (110-120 Vac) or a USB source.
There are other configurations for an indoor antenna. Some antennas have a coax connector instead of hard-wired. Some antennas have a detachable or permanent preamp.
Stick and some loop antennas connect directly to the back of the TV. This makes the antenna virtually hidden, and limits reception.
Most outside and attic antennas are directional and come in 2 basic styles, vertical profile and horizontal profile. Vertical profile antennas are a more efficient, horizontal profile antennas are more wind resistant. Some antennas have a built-in preamp. The preamp gets DC power through the coax cable, see Hardware / Amplifiers / Preamps.
|5 - 11||30 - 60||60° - 90°||moderate|
Very High Gain
|11 - 15+||60 - 85+||≈ 30°||Large|
To receive distant and spread out broadcast headings you can use an Omni Directional antenna, multiple antennas, or a rotor antenna. All of these systems use a preamp. These systems require 110-120 Vac power (house current) to run a preamp and/or rotor. A rotor system has the advantage of full gain and full 360° coverage. A high gain antenna with a built-in preamp mounted on a rotor has the highest performance.
Antenna gain is expressed on a log scale with unit dimensions of dBD or dBi. The dBD unit is used to measure gain, the dBi unit is used for calculations. Antenna gain expressed in dB usually means dBi. Most antenna gains are expressed in dBi units.
|dBi||-||decibels (dB's) above or below a Lossless Isotropic Radiator.|
|dBD||-||decibels above or below a Standard Half wave Dipole antenna with a gain of +2.15 dBi.|
Convert to dBi or dBD
ESTIMATE UHF ANTENNA GAIN FROM SIZE
UHF Antenna gain can be estimated from antenna dimensions and antenna efficiency. Efficiency can be estimated from antenna type. Gain also depends on frequency, higher frequencies have higher gains.
|G||-||Gain (dBi)||c||-||Speed of Light|
|Antenna Type||Efficiency (η)|
|Indoor Flat Antenna||20 - 30%|
|Horizontal Profile||50 - 60%|
|Vertical Profile||60 - 75%|
Estimate UHF Antenna Gain
from Efficiency and Length & Width
Most antennas are directional and have a specific reception area (main beam). The beams are relatively wide, some wider than others.
|BEAM SPREAD (d)|
|Beam Spread Calculator|
Antenna Gain Varies
Antenna gain varies with frequency. The higher the frequency (higher RF channel) the greater the gain. Advertised gains are usually for the highest frequency, and the highest gain. The gain maximum to minimum difference can be 2 dB or less for a low gain antenna, around 4 dB for a high gain antenna, and up to 6 dB or more for a very high gain antenna.
An antenna has maximum gain when the main beam is directly aligned (0°) to the signal direction. Gain decreases slightly from the beam center (0°) to the beam edge. At the beam edge the antenna gain is down by -3 dB. Past the beam edge (the -3 dB point) gain drops dramatically. Side and back lobes have a negative gain, from -10 dBi to -30 dBi or more.
Polarization is the broadcast antenna signal electric field orientation. Polarization loss occurs when the transmit antenna does not match the receive antenna polarization. Virtually all home antennas and many broadcast antennas are horizontally polarized. Some broadcast use circular polarization for better signal propagation in a cluttered and/or bad weather environment. When a mismatch occurs, the receive antenna loss is -3 dB.
Broadcast Pattern Loss
Broadcast antenna patterns can be omni directional (broadcast equally in all directions - 360°), or directional. Receive antennas outside a directional broadcast main beam will receive less power. The loss can be a few dB to 10's of dB's.
|Main Beam Loss:||0 to -3 dB|
Low Gain Antenna:
High Gain Antenna:
Very High Gain:
0 to -2 dB
0 to -4 dB
0 to -6 dB
|Polarization Loss:||0 or -3 dB|
|Broadcast Pattern:||0 to -10+ dB|