| CONTENTS | ||
| INTRODUCTION | ANTENNA THEORY | |
|
• Indoor Antennas
• Outside Antennas • Multi-Directional Antennas |
• Frequency Bands
• Antenna Gain • Reception Beam • Loss Factors |
|
INTRODUCTION
Indoor antennas can work when broadcast towers are within about 20 - 30 miles. In a cluttered environment an outside antenna may be required. An outside antenna can get signals up to 45 - 60 miles or more. An antenna preamp will improve a weak signal and reception range. A preamp can be added to any antenna. Some antennas come with a built-in or detachable preamp. Preamps require power, house current (110-120 Vac) or USB power.
Frequency Bands
Broadcast are in the VHF or UHF frequency band. Virtually all antennas today receive UHF signals, some get VHF / UHF (all FCC broadcast channels), and some get VHF-Hi / UHF. See Frequency Bands below and Tech section / Frequency Bands. Nationwide 80% of broadcast channels are in the UHF band.
Antenna Gain
Antenna gain measures the signal power an antenna captures. Gain is measured in dBi - decibels (dB's) with respect to a lossless Isotropic radiator. Many published antenna gains are in "dB", they really mean dBi.
See
below.
The larger an antenna the greater the gain, and the more narrow the reception beam. Also, symmetrical antennas
(looks the same from the front or back), have the same reception (gain) front and back.
| • | Indoor or Outdoor Antenna |
| • |
Frequency Band(s) UHF, VHF/UHF or VHF-Hi/UHF |
| • | Size: Larger has greater Gain |
| • | With or without a 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.
| INDOOR ANTENNAS |
Indoor antennas are designed to be window or wall mounted, or table top.
Flat Thin Antennas
Flat antennas at least 17 inches wide have good UHF / VHF-Hi reception (gain), and are the most popular. Antennas less than about 17 inches wide do not get VHF signals and have less gain.
Loop Antennas
Loop antennas at least 6 inches in diameter have good UHF reception and are the most efficient for UHF signals (no VHF reception).
Rabbit Ears
Rabbit Ears work well for VHF signals. These antennas are an adjustable dipole, and can extend from 6 to 52 inches long at different angles.
Other Configurations
There are many other configuration with varying options.
| Typical Performance | |
|---|---|
| Gain | 2 to 4 dBi |
| Reception Beam | 60° to 70° |
| Range | 20 to 30 miles |
ClearStream Eclipse Sure Grip Indoor HDTV Antenna Dim: 10" x 8.6" x 0.4"
|
 ClearStream Eclipse Amplified Sure Grip Indoor HDTV Antenna Dim: 10.1" x 8.6" x 0.4"
|
 ClearStream VIEW Wall Frame Amplified Antenna Frame: 14.25" x 18.3" x 0.8" Antenna: 12" x 16"
|
 ClearStream FLEX Ultra-Thin Amplified Indoor HDTV Antenna Dim: 14.25" x 18.3" x 0.04"
|
 ClearStream Horizon Amplified Indoor HDTV Antenna with Coaxial Cable Dim: 14.25" x 18.3" x 0.0.04"
|
| OUTSIDE ANTENNAS |
Most antennas are directional and come in 2 basic styles, vertical profile and horizontal profile. Vertical profile antennas are more efficient. Horizontal profile antennas are a little more wind resistant.
| Antenna |
High Gain |
Very High Gain |
|---|---|---|
| Gain | 5 to 10 dBi | 11 to 20 dBi |
| Beam | 60° to 70° | 15° to 35° |
| Range | 45+ Miles | 60+ Miles |
| Size | Moderate | Large |
 ClearStream 1MAX Indoor / Outdoor TV Antenna
|
 ClearStream 5 UHF VHF Ultra Long Range Outdoor DTV Antenna
|
 ClearStream MAX-V Long Range Indoor / Outdoor TV Antenna
|
 Antennas Direct Element Unidirectional UHF VHF Attic Outdoor HDTV Antenna
|
 ClearStream 2 RV TV Antenna
|
 ClearStream MAX-V PRO UHF/VHF Indoor/Outdoor HDTV Antenna
|
 Antennas Direct SR15 Unidirectional UHF Attic Outdoor HDTV Antenna
|
 91XG Uni-Directional Ultra Long Range DTV Antenna
|
 DB8e Extreme Long Range Bowtie HDTV Antenna
|
| MULTI-DIRECTIONAL ANTENNAS |
Rotor Antennas
These antennas can receive signals from all directions. The rotor requires a power / control cable run to the outside rotor motor. The antenna does take a little time to change directions. The rotation is plus or minus 180° (so the coax cable doesn't wrap around the mast).
A rotor can be added to any antenna, some antennas come with a rotor.
|
Rotor Antenna
• 360° coverage. • ± 180° rotation. • Takes a little time to change angles. • Power / Control Cable to outside rotor. |
Omni Directional Antennas
These antennas can receive signals from all directions simultaneously. They are relatively compact and widely used in marine and recreation vehicles, and homes. Most have built-in preamps. Overall performance is modest, a strong to high normal signal is required.
|
Omni Antenna
• 360° simultaneous coverage. • Modest range. • Small and compact. • Most have a built-in preamp. |
| ANTENNA THEORY |
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.
Your home location and antenna are the main factors that determine reception.
| Placement | -- | Relatively clear line-of-sight to towers. |
| Height | -- | The higher the antenna, the greater the signal density and the lower the ground reflection loss. |
| Size | -- | The larger the antenna the more signal captured (the greater the gain) and the more narrow the reception beam. |
| FREQUENCY BANDS |
Most stations are in the UHF band -- more RF channels. The VHF band is sometimes subdivided into VHF-Lo and VHF-Hi.
| Band(s) | RF Channels | Frequency | ||
|---|---|---|---|---|
| VHF | 2-13 | 54-216 MHz | ||
| UHF | 14 - 51 | 470-698 MHz | ||
|
VHF-Hi / UHF |
07 - 13 14 - 51 |
174-216 MHz 470-698 MHz |
||
|
VHF / UHF |
02 - 13 14 - 51 |
54-216 MHz 470-698 MHz |
||
UHF antennas with a preamp and close to a Cell tower (4G/5G) may get strong signals that interfere with the preamp. You may lose some or all TV signals. Some preamps have a Cell signal (4G/5G) filter to reduce or eliminate interference.
VHF antennas with a preamp and close to a commercial FM tower may get strong signals that interfere with the preamp. You may lose some or all TV signals. Some preamps have an FM Trap to reduce or eliminate interference. The Trap may slightly reduce RF channel 6 reception.
Also see;
-- Tech section / Frequency Bands,
-- Hardware section / Amplifiers.
| ANTENNA GAIN |
Antenna gain is expressed on a logarithmic scale with unit dimensions of dBD or dBi. The dBD unit is used by manufacturers to measure gain, the dBi unit is used for calculations and publications.
| 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. |
| dBi | = | dBD | + | 2.15 |
| dBD | = | dBi | - | 2.15 |
|
Convert to dBi or dBD |
Also see Tech section / The Decibels (dB) Scale
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.
| Variables | ||||||
| G | - | Gain (dBi) | c | - | Speed of Light | |
| A | - | Area | π | - | Pi (3.14159...) | |
| f | - | Frequency (Hz) | ||||
| η | - | Efficiency (%) | ||||
| 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 |
||||||||||||
Frequency |
| RECEPTION BEAM |
Most antennas are directional and have a specific reception area (main beam). The beams are relatively wide, some wider than others.
| RECEPTION PATTERN |
|
| RECEPTION AREA |
|
| BEAM SPREAD (d) |
|
| Beam Spread Calculator | ||
|---|---|---|
| Beamwidth: | ° (Degrees) | |
| Range: | ||
|
Beamwidth | ||
| LOSS FACTORS |
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.
Beam Loss
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 Loss
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. A home antenna that is outside a directional broadcast main beam will receive less power. The loss can be a few dB to 10's of dB's.
Summary
| SOURCE | Loss |
|---|---|
| Main Beam Loss: | 0 to -3 dB |
| Gain Variation: 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 |
|
TV Antennas |