Television Antenna
Types and Options

CONTENTS
INTRODUCTION		ANTENNA THEORY
• Indoor Antennas • Outside Antennas • Multi-Directional Antennas		• Frequency Bands • Antenna Gain • Reception Beam • Loss Factors

INTRODUCTION
Indoor antennas can work for towers within about 20 miles. In a cluttered environment an outside antenna may be required. A preamp will improve weak signals. An outside antenna can get signals up to 45 - 60 miles or more. An antenna preamp will improve a weak signal, and can be added to any antenna. 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, many also get VHF or VHF-Hi signals. Nationwide 80% of TV channels are in the UHF band. Only 15% are in VHF-Hi, and 5% in VHF-Lo.

TV Broadcast Frequency Bands

Also see

-- Frequency Bands (below). -- Tech / Frequency Bands.

Antenna Gain
Antenna gain is the signal power captured and is measured in dBi. It is sometimes expressed in dB, but they really mean dBi. Gain is a better measure of antenna performance than published range (often exaggerated). See Antenna Gain below.

Reception Beam
Most antenna are directional with a reception beam width that varies with antenna gain. Symmetrical antennas (looks the same from the front and back), have the same reception beam and gain in the front and back. See Reception Beam below.

Size
The larger an antenna the greater the gain, and the more narrow the reception beam.

Summary

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 are relatively low gain. Most are symmetrical and have front and rear reception. Walls will reduce a signal, metal obstructions block a signal. A preamp can improve a weak signal.

Antenna Location
As High as Possible
In or Near a Window
Pointed at Towers

Typical Specifications
Antenna Gain:	2 - 5 2 - 9	dBi (UHF) dBi (VHF)
Range:	20 - 30	miles
Reception Beam:	60 - 90	degrees

Common Configurations
MOUNTING	-- Window -- Wall (Higher Better) -- Table Top
BAND	-- VHF / UHF -- VHF-Hi / UHF -- UHF
PREAMP	-- Optional -- Built-in -- Detachable
Preamps require USB power.

Basic Antenna Types
Loop Antenna -- UHF -- Gain: 4 to 5 dBi -- 6 to 9 inch diameter
Flat Thin Antenna -- VHF-Hi / UHF -- UHF (< 17 inch wide) -- Gain: 2 to 4 dBi
Rabbit Ears - Dipole -- VHF -- Gain: 2 to 9 dBi -- Extends 13 to 52 inches -- Adjustable angles

Combination Antennas
Some antennas combine VHF and UHF
elements to get both frequency bands.

Outside antennas have greater gain and are mounted higher and in the open where the signal density is greater.

Antenna Profiles
There are 2 basic antenna profiles, horizontal and vertical. Vertical profile antennas are a little more efficient. Symmetrical vertical antennas have both front and rear reception unless they have a reflector. Antennas with a reflector have more gain.

Horizontal Profile
Yagi (VHF)
Log-Periodic (UHF)

Vertical Profile
Loop Array / Dipole		Bowtie Reflector
Front & Rear Reception		Higher Gain

High Gain and Very High Gain Antennas
Most outside antennas are High Gain. Very High Gain antennas have greater range, are larger, and have a more narrow reception beam. Antenna types include Yagi, Lop Periodic, Loop, Bowtie, Dipole, or a combination of types.

Some antennas have a built-in preamp for weak signals. See Hardware / Amplifiers.

Rotor Antennas
These antennas can receive signals from all directions. The rotor requires a power and 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.

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.

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.

All antenna receive UHF signals, some also get VHF or VHF-Hi.

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 (VHF-Lo) reception.

Also see Tech / Frequency.

Television antenna gain is measured in dBi, sometimes shorten to dB. Some manufacturers measure gain dBD's, which is about 2 dB lower than dBi. Both dBi and dBD use a base 10 logarithmic scale.

ESTIMATE UHF ANTENNA GAIN FROM SIZE
UHF Antenna gain can be estimated from antenna dimensions and efficiency . Efficiency can be estimated from antenna type. Gain also depends on signal frequency, the higher the frequency the greater the gain.

Most antennas are directional and have a specific reception area (main beam).

RECEPTION PATTER

BEAM SPREAD (d)

Beam Spread Calculator
Beamwidth:		° (Degrees)
Range:		Miles kilometers
Beamwidth Range Beam Spread Calculate / Re-calculate

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

OTA DTv Antennas