RF Theory Flashcards
high range of frequency signal which has a specific amplitude, frequency, and phase levels, but it does not hold any data.
Carrier Wave
This signal is what holds the message or traffic. Signals are sent through what is called a modulator to attach the data onto a signal and is then sent out across the airwaves to a destination.
Modulating Signal
is process by which voice, music, and other “intelligence” is added to the radio waves produced by a transmitter.
Modulation
the fluctuations in power (amplitude) of the wave carries the data.
Amplitude modulation (AM)
If this input signal is added to the pure carrier wave, it will thereby change the frequency of the carrier wave. In that way, users can use changes of frequency to carry speech information.
Frequency Modulation (FM)
535 kHz - 1605 kHz
AM radio frequency
87.9 MHz - 107.9MHz
FM radio frequency
the decrease in a property, as energy, per unit of a wave of a beam of particles, which increases as a result of absorption, scattering, spreading in three dimensions, etc.
Attenuation
is the loss of signal strength in networking cables or connections.
Attenuation (laymens)
A method to help with ______ (besides shortening the distance) is through the use of repeaters or amplifiers.
Attenuation
the amplification of a signal which can compensate for losses
Gain
uses an RF amplifier to increase the signal strength
Active Gain
uses no extra amplification and relies fully on the directionality of the antenna for increased RF energy in a desired direction.
Passive gain
based on a “Bel”, a unit of strength named after early telecommunications pioneer, Alexander Graham Bell.
__ is a measure of relative power and cannot be converted into watts
dB
decibel relative to milliwatt.
the amount of power that an antenna or amplifier is able to produce, or how much signal is present at a site.
= dB+30, so 0dB is 30dBm
dBm
you add 3 dBm you will double your value
1 Watt = 30dBm
2W = 33dBm
and vice versa
1W = 30 dBm 0.5W = 27 dBm
Rule of 3
to add 10 times the power, you add 10dBm
1W = 30 dBm
10W = 40 dBm
rule of 10
Signal loss due to a long distance of travel or running into objects is called what?
Attenuation
ensures that as much RF energy captured by the antenna is passed through the transmission line and onto the modem
Matching
when two adjacent devices on a circuit have different impedances
Impedance mismatch
describes the ratio of mismatch. If the VSWR is high enough, the standing wave can cause signal distortion and damage the transmitter.
VSWR
These systems allow communication in only one direction.
Simplex
each participant can transmit and receive, but only one station can transmit at a time.
Half-Duplex
Enables each transmitters to send and receive at the same time.
Full-Duplex
