Annex B04 Wave Propagation & Radio Frequency Communication Flashcards
Three (3) atmospheric propagation effects associated with radio wave propagation
Reflection (reflecting off a medium at the same angle it hits the medium i.e. angle of incidence vs angle of reflection)
Refraction (passing through a medium and changing speed and direction)
Diffraction (bending around an object)
Propogation
Disturbance through a medium
Two (2) principle ways in which radio waves travel through from a transmitting antenna to a receiving antenna
Ground Waves (Ground/Space Waves) Sky Waves
Three (3) factors that must be considered in the transmission of a surface wave to reduce attenuation
Density of ionization (dependent on time of day, time of year, location, sunspot #, solar cycle)
Frequency of the radio wave
Angle of incident (angle at which the wave enters the layer)
Three (3) frequencies uses in frequency planning considerations
Maximum Usable Frequency (MUF: highest during day)
Lowest Usable Frequency (LUF: lowest during night)
Optimum Working Frequency (OWF/FOT: 85-90% of MUF)
Six (6) requirements for a simple communication system
Transmitting Equipment Transmission Line Transmitting Antenna Medium Receiving Antenna Receiving Equipment
Why is radiotelephone the most useful method of military communication
Directness, convenience, ease of operation
Disadvantages of Radiotelephone Communications
Transmissions may be unreadable because of static due to EMI, enemy interference or high local noise levels
Unpredictable due to wave propagation effects
Local noise may interfere with comm
Two (2) primary modes of operation for radiotelephone communications
Half Duplex: Can only receive or transmit at one time i.e. radio
Full Duplex: Can receive and transmit at same time i.e. cell phone
Five (5) primary frequency bands used by USMC
HF: 1.6-30MHz VHF: 30-300MHz UHF: 300MHz-3GHz SHF: 3-30GHz EHF: 30-300GHz
Two (2) main disadvantages associated with frequencies above 30 MHz
Frequencies above 30 MHz are not normally refracted by the atmosphere
Ground wave is minimal
Modulation vs Demodulation
Modulation: impressing intel upon a transmission medium (carrier)
Demodulation: removing intel from the medium
Amplitude Modulation vs Frequency Modulation
AM: Varying the amplitude of an electromagnetic carrier frequency IAW the intel to be transmitted by the carrier
FM: Varying the frequency of the carrier IAW the intel to be transmitted by the carrier. Amplitude is kept constant
Two (2) additional frequencies created when a carrier wave is impressed with intel creating a modulated wave
Upper Sideband: (USMC)
Lower Sideband (USN)
Single Sideband used by the USMC
Single Sideband Suppressed Carrier (SSB-SC)
