Communication Flashcards
(45 cards)
Define wavelength
the distance between two equivalent points in a wave, measured in meters
Define frequency
the number of cycles of an EM wave propagating past a given point each second, measured in Hz
What is the relationship of freq to wavelength
As frequency increases, wavelength decreases and vise versa
What is amplitude
measure of intensity carried by a EM wave….the height
What is Phase
Section of a complete wave cycle corresponding to an angular offset from a specified reference at a given time
What is EM propagation
What happens as a wave travels through a medium/ encounters matter….often results in signal attenuation/distortion.
Types: Absorption, Reflection, Scattering, Refraction, Diffraction
Define modulation
process of adding information to a carrier wave
define demodulation
process of removing information from a carrier wave
Define Amplitiude modulation
carrier signal’s amplitude varies with the changing amplitudes of the modulating signal…example is HAVEQUICK
Define Frequency modulation
Modulating signal causes the carrier frequency to vary…example is SINCGARS
Define Phase Modulation
Information is conveyed by varying the phase of carrier wave…used to allow higher data rates
Describe the concept of Link Budgeting
To close the link, total gains must overcome total losses so that the Signal Noise Ratio at the receiver is sufficient
Define Gains
Signal strength increased
Define Losses
Signal strength reduced
What are the two main types of antennas
Isotropic = omnidirectional with less focus Directional = aimed with focused power
Define Multiplexing
Many signals COMBINED on one channel
Define Multiple access
usage of a common comm resource by different users
Whats the difference between Frequency-Division Multiple Access, Time-Division Multiple Access, Code-Division Multiple Access, and Demand Assigned Multiple Access
FDMA = Users assigned different freqs TDMA = Users are assigned different time slots on shared channel CDMA = Common freq and time allocation, but users have PRN codes assigned DAMA = channel assigned based on immediate traffic demands
What is the differences between EM noise, EM interference and jamming
Noise is ambient, noncoherent
Interference is specific, coherent signal that negatively impacts
Jamming is intentional interference , but needs power, Frequency, and Access to the receiver to work
What are the 3 requirements to jam comms
power, frequency, and access to the reciver
What are jamming countermeasures for CDO
Passive (preeemptive) - in place before an attack
Active (reactive) - implemented during or after an attack
Describe uplink and downlink SATCOM jamming
Downlink: at the terrestrial receiver, affects local area only (LOS)
Uplink: at the satellite, affects Large-area effect (BLOS)
Illustrate the NIPRNet architecture
Public Internet –> DoD Gateway –> AF Gateway –> AF Base Boundary –> NIPRNet Host level
Illustrate the SIPRNet architecture
DoD SIPRNet –> AF Gateway –> AF Base Boundry –> SIPRNet host level
