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TV Antennas

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INTRODUCTION
An indoor antenna works when broadcast towers are within 20 to 25 miles. An outdoor antenna can get signals from 60 miles or more. An antenna preamp will pull-in weaker signals, and can be added to any antenna. Some antennas have a built-in preamp.

Digital vs Analog Antenna
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 in the VHF or UHF band, carrier modulation (digital or analog) does not effect antenna reception.

FUNDAMENTALS

The larger the antenna the more signal captured and the greater the antenna gain. As gain increases beamwidth narrows. Signals not in the main beam are greatly reduced. VHF antennas have longer wavelengths and are larger than UHF antennas. A VHF/UHF antenna combines a VHF and UHF antenna into a single arrangement. A built-in coupler is used to combine VHF and UHF signals to the antenna output connection.

FREQUENCY BANDS

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 antennas do not get the lower VHF channels RF 2 - 6 (VHF-Lo Band).

TV Antenna Configurations
Band(s) RF Channels Frequency
VHF 2-13 54-216 MHz
UHF 14 - 69 470-806 MHz
VHF-Hi / UHF 7 - 69 174-216 MHz
470-806 MHz
VHF / UHF 2 - 69 54-216 MHz
470-806 MHz

Also see TV broadcast 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
Antenna 3D Plot
RECEPTION AREA
antenna coverage
BEAM SPREAD (d)
Beam Spread


Beam Spread Calculator
Beamwidth: ° (Degrees)
Range:

Beamwidth
Range

Beam Spread



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ANTENNA GAIN

Antenna gain is expressed in 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.

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


ANTENNA TYPES

INDOOR ANTENNA

Indoor Antennas

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. Many have a built-in preamp, some are detachable. The preamps are powered by 110-120 Vac (house current) and/or a USB connection.

Indoor Antenna Pattern
Flat Thin Rectangular Antenna
- Efficient, Light Weight
- Size: ≈ 4x4 to 12x12 inches
- Mount: Stand, Wall, Window
Table Top Antenna
- Variety of Styles
- Some use Rabbit Ears for VHF,
- Some use a Loop for UHF


Typical Performance
Gain
2 to 4 dBi
Range
20 - 25 Miles
Beam
≤ 120°

Stick and some loop antennas connect directly to the back of the TV. This makes the antenna virtually hidden, and limits reception.

Note; flat indoor antennas pick up UHF broadcast better than VHF broadcast. The size limits VHF reception.



OUTSIDE ANTENNA
Outdoor Antennas

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 pre-amp. The preamp gets DC power through the coax cable.

ANTENNA Gain
dBi
>Range
Miles
Beam
Degrees
Size
Attic / Outside 5 - 11
High Gain
30 - 60 60° - 90° moderate
Outside 11 - 15+
Very High Gain
60 - 85+ ≈ 30° Large

Range vs Antenna Gain
Moderate Gain Antenna Pattern High Gain Antenna Pattern

MULTI-DIRECTIONAL ANTENNAS
A multi directional antenna system is required for distant and spread out broadcast headings. Most of 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.

  • Multiple Antennas
  • Omni Directional (360°) Antenna
    • relatively small.
    • requires a preamp.
    • well suited for marine or RV use.
  • Rotor Antenna
    • 360° coverage.
    • takes a little time to change angles.
    • Highest performance.

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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

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. 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.

Summary

Antenna Loss
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

-2 to -6 dB loss is not uncommon.
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TV Antennas