SA1 prt 2

RF propagation types

Space radio propagation and Terrestrial propagation.

Ground wave frequency bands

MF, HF, VHF, UHF.

Ground wave components

Surface wave and Space wave (Direct, Ground reflected).

Sky wave frequency bands

High MF, low VHF.

Components of sky wave

Ionospheric and Meteor Burst.

LOS frequency bands

VHF, UHF, SHF.

LOS component

Microwave.

Scattered wave components

Tropospheric scatter (VHF, UHF) and Ionospheric scatter (high MF, low VHF).

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

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.

Types of linear polarisation

Horizontal and vertical.

Types of circular polarisation

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.

Types of fading

Interference, Polarisation, Absorption, Skip.

Causes of interference fading

Multipath, variations in ionosphere.

Causes of polarisation fading

Polarisation changed by change in medium.

Causes of absorption fading

Atmospheric anomaly.

Causes of skip fading

Edges of skip zone.

Dipole antenna polarisation

Horizontally polarised.

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.

Effects of terrain - Trees/foliage

Attenuate, scatter, reflect.

Effects of terrain - Hills/valleys

Limit range, reflect, diffract.

Antenna sighting considerations

Correct selection, Height, Polarisation.

Man-made effects of tunnels

Channelling, high absorption.

Man-made effects of buildings

Reflect, diffract, limit LOS.

Man-made effects of wire lines

Absorb power, induce noise.

Man-made effects of high travelled roads

Noise/electrical interference.

Man-made effects of generators

Noise/electrical interference.

Man-made effects of 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

Troposphere, Stratosphere, Ionosphere.

D region characteristics

60-80 km, absorbs or attenuates.

E region characteristics

80-160 km, refracts but still attenuates.

F1 region characteristics

160-210 km, refracts.

F2 region characteristics

210-500 km, refracts and combines at night.

Regular ionospheric variations

Solar cycle, Daily, Seasonal, Latitude, Height.

Irregular ionospheric variations

Solar flare, Sporadic E.

MUF meaning

Maximum Usable Frequency.

OWF meaning

Optimal Workable Frequency.

ALF meaning

Absorption Limiting Frequency.

Skip modes

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

Parabolic, Array, Horn.

LEO meaning

Low Earth Orbit - Data, comms, email.

MEO meaning

Medium Earth Orbit - Nav, GPS.

HEO meaning

High Earth Orbit - Polar coverage.

GSO meaning

Geosynchronous Orbit - Earth obs, comms.

GEO meaning

Geostationary Orbit - Earth obs, comms.

Sat footprint types

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 meaning

Field Expedient Antenna.

FEA characteristics

Lightweight, Height advantage, Redundancy.

FEA cable type

RG58/u.

FEA connector types

BNC, TNC, N Type, SMA.

HCLOS meaning

High Capacity Line of Sight.

HCLOS key factors

Height, LOS, Industrial noise.

7th Signal Regiment subordinate units

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.