Essential TV Antenna and Satellite Concepts
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Antenna Amplifiers
Number of amplifier types: Two main types for typical antennas: Monochannel (single channel) and Wideband.
Noise Figure: Indicates the noise level entering the amplifier's signal input.
Signal Quality
Ideal Signal-to-Noise Ratio (S/N) for a perfect image (dB): 57 to 80 dB, with 46 dB being the minimum for acceptable TV viewing.
Standard TV Antenna Impedance: Typically 300 ohms.
Types of Amplifiers
Single-channel amplifiers:
- Amplifier with one input and two outputs.
- Amplifier with two inputs and two outputs.
Power Amplifier Function: Amplifies the signal, allowing for small variations in channel amplification.
TV Antenna Installation
Essential Elements for Successful TV Antenna Installation:
- Antenna
- Cable
- Amplifiers
- Filters / Separators / Attenuators
- Equalizers
- Distributors
- Splitters
- User Outlet
Signal Management Components
Types of Filters:
- High-pass
- Low-pass
- Band-pass
- Band-stop (rejects a specific band)
Antenna Coupler Function: Used to join signals from two antennas.
Distributor Function: Distributes the signal to different outlets.
Bypass Function: Distributes the signal to different branches while maintaining impedance matching.
Masthead Amplifier: A power amplifier placed near the TV mast to boost the signal before it travels down the cable.
Extension Attenuation: Signal attenuation between the antenna and the amplifier.
Bending Moment: Flexure experienced by a metallic element fixed at its ends when a force is applied.
Signal Levels
VHF Signal Level at User Outlet: 57 - 80 dB.
FM Signal Level: 40 to 70 dB.
Digital Signal Thresholds (dB):
- QPSK: 47-77 dB
- 64-QAM: 45-70 dB
Satellite Systems
Fundamentals
Physical Basis of a Parabolic Antenna: Concentrates the signal onto the dish and directs it to the LNB (Low-Noise Block).
Clarke Orbit: Geostationary orbit.
Geosynchronous (Satellite): Rotating at the same angular velocity as the Earth.
Geostationary Satellite Altitude: Approximately 35,806 km.
Satellite Orbit Perturbations: Mainly due to the Sun's gravitational pull and Earth's elliptical orbit.
Sun's Angle of Eclipse on Satellite and Duration: 17.36°, lasting 69' 15".
Pronounced Eclipse Phenomenon: During equinoxes, March 21st and September 22nd.
Frequency Bands and Signal Management
Satellite Frequency Bands: C-band (4 GHz) and Ku-band (12 GHz).
Geosynchronous Satellite Uplink/Downlink Frequencies: Uplink 14 GHz, Downlink 12 GHz.
Frequency Differentiation: To avoid interference.
Interference Avoidance Technique: Change polarization.
Satellite Frequency Changer: Transponder.
Satellite Coverage Area: The area where the satellite signal can be received, also called "footprint".
Satellite Dish Types
- Prime Focus
- Offset
- Cassegrain
- Flat Prime Antenna
DTH and DBS
DTH (Direct-to-Home): Satellite with medium power.
DBS (Direct Broadcasting Satellite): Satellites with high power.
Earth Geometry and Satellite Alignment
Earth Parallels: Divisions of land parallel to the Equator, including the Equator itself.
Terrestrial Meridians: Divisions of land from pole to pole; the Greenwich meridian is 0°, and there are 180.
Azimuth: Horizontal angle to rotate the dish to locate a satellite.
Elevation: Angle to raise the dish to locate a satellite.
Polarization Skew: Angle to rotate the LNB to receive the satellite signal correctly.
Calculating Alignment Angles
Methods for Calculating Alignment Angles:
- Mathematical calculations
- Tables and graphs for each satellite, cable provider, and country
- Abacus or nomogram
Magnetic North and Inclinometer
Magnetic North Pole Location: Approximately 5 to 6 degrees to the right of the geographic North Pole.
Inclinometer Use: To measure elevation.
Inclinometer Function: To adjust antenna elevation, polarization, and skew.
LNB (Low-Noise Block)
LNB Function:
- Receives the signal
- Converts it to Intermediate Frequency (IF) (950 to 2150 MHz)
- Amplifies the signal
LNB Characteristics:
- Sensitivity
- Operating frequency
- Polarity
LNB Types:
- Single (Universal)
- Double / 4 outputs
- Monobloc (Two satellites)
IF Signal Purpose: To reduce cable attenuation and signal losses.
Frequency Bands
B-II VHF Band: Used for FM radio.
B-IV Band: Includes TV channels 21 to 69.