ANTRC170 Training Unit 1 Basic Troposcatter Theory Basic
AN/TRC-170 Training Unit 1 Basic Troposcatter Theory
Basic Troposcatter Theory Overview • Earth’s Atmosphere • Troposcatter communications • Factors affecting • • Take-off angle Diversity Basic Tropo Theory AN/TRC 170 Training 2
Earth’s Atmosphere • Troposphere: lowermost portion of the atmosphere • Weather occurs in this layer of atmosphere • Weather and atmospheric changes affect the troposcatter signal Basic Tropo Theory AN/TRC 170 Training 3
Troposcatter Communications • Uses microwave radio to communicate through the atmosphere “Over-the-Horizon” • Signal can be scattered • Signal can be diffracted • Equipment can also be used in “Line-of-Sight” Basic Tropo Theory AN/TRC 170 Training 4
Troposcatter Communications Transmission of the signal is affected by: • Scattering: loss of signal into space • Fading: Short or long term variations in signal level Basic Tropo Theory AN/TRC 170 Training 5
Factors Affecting Troposcatter Links Scattering • • • Main part of signal is lost Random phenomenon Only the refracted portion is useable Basic Tropo Theory AN/TRC 170 Training 6
Factors Affecting Troposcatter Links Long Term Fading – Variations in Signal Level • Caused by weather, seasonal changes Basic Tropo Theory AN/TRC 170 Training 7
Factors Affecting Troposcatter Links Short-Term Fading: Sudden, unpredictable drops in signal for 0. 03 – 3 sec • Ex: Frequency Selective Fading Basic Tropo Theory AN/TRC 170 Training 8
Take-off Angle • Take-off Angle is the angle the antenna has to be set at in order to transmit over the horizon. • Normal take-off angles for troposcatter links range from 0 -5 degrees. Basic Tropo Theory AN/TRC 170 Training 9
Diversity • • Diversity helps to overcome fading Combines two or more signals Signals have independent paths The signals may arrive at different times or arrive stronger/weaker Basic Tropo Theory AN/TRC 170 Training 10
Angle Diversity • • Diversity reception in which beyond-the-horizon troposcatter signals are received at slightly different angles. The equipment combines the paths in order to prevent signal loss or degradation. Basic Tropo Theory AN/TRC 170 Training 11
Space Diversity • Uses 2 antennas at each end of a tropo link • Improves the receive signal over any single path • Requires 100 wavelength separation • One antenna is used for transmit and receive, and the second for receive only. Basic Tropo Theory AN/TRC 170 Training 12
Frequency Diversity • Uses one antenna at each end • Uses two frequencies at each end. Receiving Rx 1 & Rx 2 Transmitting Tx 1 & Tx 2 Transmit & Receive Transmit Signal Basic Tropo Theory AN/TRC 170 Training Transmit & Receive 13
Questions? Basic Tropo Theory AN/TRC 170 Training 14
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