Comm Fundamentals Flashcards
Define AM, PM, FM
AM- carrier signal’s AMPLITUDE varies with changing amplitude of the signal
PM- Phase mod is used in DIGITAL comms with high transmission speeds to vary the phase of the carrier wave
FM- carrier wave’s FREQUENCY is varied
Describe Gain, Loss, and Link Budgeting
Gain- Signal strength is increased (using antennas and amplifiers)
Loss- signal strength is reduced (absorbtion, scattering, reflection etc.)
Link Budgeting- analysis balancing transmitter, channel, receiver and noise environment parameters to achieve desired signal characteristics
! Total gains need to be greater than total loss so SNR is sufficient !
Discuss antenna characteristics and include two basic antenna types
Characteristics: TX/RX pattern, gain, polarization, and shape
Types: Isotropic (omni-dir) and Directional
What is the purpose of multiplexing. What is the difference between time-division, freq- division, and code-division?
Multiplexing combines to or more signals over a shared channel to increase information passed in the allotted channel
Frequency Division- different signals modulated into separate freq bands and summed together
TD- 2+ signals TXd as sub channels over one channel. Each signal has a specific time slot to TX
CD- deconflicion of shared bandwidth by frequency and time
Identify the purpose of multiple access to munication architectures and describe CDMA, TDMA, FDMA,and DAMA
Multiple access is the usage of a common communications resource by different users distributed at diff locations
FDMA- users within a medium are assigned different frequency bands usually with a small adjacent guard band
TDMA- users share a common channel by allocating different time slots to each user
CDMA- all users share a common frequency band and time allocation
DAMA- assigning the channel according to the immediate traffic demand based on priority
Describe the difference between EM noise interference and jamming
Noise- incoherent radiation negatively impacting the signal
Interference- specific coherent signal that negatively impacts an INTENDED signal or equipment performance
Jamming- intentional interference
Identify the three things a jammer needs to be effective
Power
Frequency
Access to the receiver
Describe jamming CM techniques for use in contested degraded and operationally limited environments
Passive- (preemptive) Low Probability of detect waveforms, freq hopping,beam shaping
Active- (reactive) add more power, change freq, antenna mulling
Describe a downlink and uplink SATCOM jamming and the impact to users
Downlink- interferes w/ reception of downlink signal at the ground receiver (impacts LOS)
Uplink- interferes w/ reception of the uplink at the satellite (impacts BLOS)
Discuss basic terms associated with EM waves and describe the relationship between wavelength and frequency
Wavelength is the distance between two points in a wave (measured in meters). Frequency is the # of cycles of an EM wave propagating past a given point each second (measured in Hz).
As frequency increases wavelength decreases
