SA1 prt 2

RF propagation - 2 types Space radio propagation, Terrestrial

Ground wave - which bands MF, HF, VHF, UHF

Ground wave components Surface wave, Space wave (Direct, Ground reflected)

Sky wave - which bands High MF, low VHF

Sky wave components Ionospheric, Meteor Burst

LOS - which bands VHF, UHF, SHF

LOS component Microwave

Scattered wave components Tropospheric scatter (VHF, UHF), Ionospheric scatter (high MF, low VHF)

4 Parts of an antenna Driven element, Load, Transmission line, Ground/earth

Isotropic source (definition) Theoretical source emitting EM waves uniformly in all directions/intensity, forming a sphere

Directivity (definition) Ratio of radiation intensity in a given direction to the radiation intensity averaged over all directions; expressed as Gain (dBi)

Radiation patterns (3) Omni-directional, Bi-directional, Uni-directional

Impedance (definition) Relationship between voltage and current at any point in an AC circuit

Polarisation (definition) Property of an EM wave describing the orientation of the electric field vector

Linear polarisation types Horizontal and vertical

Circular polarisation types Right/Left hand circular

Resonant antenna Works effectively on all frequencies

Non-resonant antenna Works on specific frequencies efficiently

Grounding methods Earth, equipment, chassis; counterpoise, GND screen, GND rods and straps

VSWR (definition) Measure of impedance mismatch between transmission line and load - lower is better; imperfections cause reflections

4 Types of Fading Interference, Polarisation, Absorption, Skip

Fading - Interference cause Multipath, variations in ionosphere

Fading - Polarisation cause Polarisation changed by change in medium

Fading - Absorption cause Atmospheric anomaly

Fading - Skip cause Edges of skip zone

Dipole antenna polarisation Horizontally polarised

4 Mechanisms of propagation Reflection, Refraction, Diffraction, Scattering

Reflection (definition) Bouncing back when it collides

Refraction (definition) Bending through mediums (free electron)

Diffraction (definition) Bending past an aperture

Scattering (definition) Loss in strength from splitting apart

Terrain effects - Trees/foliage Attenuate, scatter, reflect

Terrain effects - Hills/valleys Limit range, reflect, diffract

Antenna sighting considerations (3) Correct selection, Height, Polarisation

Man-made effects - Tunnels Channelling, high absorption

Man-made effects - Buildings Reflect, diffract, limit LOS

Man-made effects - Wire lines Absorb power, induce noise

Man-made effects - High travelled road Noise/electrical interference

Man-made effects - Generators Noise/electrical interference

Man-made effects - Radio stations Noise interference

Ionisation process (order) Sun emits ionising radiation -> radiation strikes atom -> electron ejected -> imbalance creates free electron + positive ion -> recombination

Ionosphere layers (3) Troposphere, Stratosphere, Ionosphere

D region 60-80 km, absorbs or attenuates

E region 80-160 km, refracts but still attenuates

F1 region 160-210 km, refracts

F2 region 210-500 km, refracts and combines at night

Regular ionospheric variations (5) Solar cycle, Daily, Seasonal, Latitude, Height

Irregular ionospheric variations (2) Solar flare, Sporadic E

MUF Maximum Usable Frequency

OWF Optimal Workable Frequency

ALF Absorption Limiting Frequency

Skip modes (2) Skip distance, Skip zone

Sat uplink process (order) Uplink baseband filter -> Low noise amp -> Translator (Local Oscillator) -> High power amp -> Downlink baseband filter

Sat antenna types (3) Parabolic, Array, Horn

LEO Low Earth Orbit - Data, comms, email

MEO Medium Earth Orbit - Nav, GPS

HEO High Earth Orbit - Polar coverage

GSO Geosynchronous Orbit - Earth obs, comms

GEO Geostationary Orbit - Earth obs, comms

Sat footprint types (3) Global, Regional, Spot

Scintillation (definition) Undesired transient charges in carrier frequency arising from the modulation process

Depolarisation - cause Rain

Sun outage effect Sun directly behind satellite, degrading the signal

FEA Field Expedient Antenna

FEA characteristics (3) Lightweight, Height advantage, Redundancy

FEA cable type RG58/u

FEA connector types (4) BNC, TNC, N Type, SMA

HCLOS High Capacity Line of Sight

HCLOS key factors (3) Height, LOS, Industrial noise

7th Signal Regiment subordinate units (4) 71 SQN, 72 SQN, 73 SQN, OSS

71 SQN troops 120 TP NRT, 122 TP TECHSIGINT

72 SQN troops 693 TP Field EW, 643 TP Field EW, 222 TP Field EW

73 SQN troops 547 TP Scout, 201 TP EA, 273 TP PCS

OSS elements Transport, CIS, Q Store