Rf Theory

Front 1

electromagnetic (EM) spectrum

Back 1

This is the range of all possible electromagnetic radiation, also referred to as 'spectrum'.

Front 2

alternating current (AC)

Back 2

Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current.

This is the type of electrical current that an RF signal starts out as in a Tx, before is travels through a copper conductor (typically a coax cable) ending up being radiated out of an antenna element in the form of an electromagnetic wave.

Front 3

waveform

Back 3

Also known as a sine wave, this is word that describes the basic shape and form of an AC signal.

Front 4

unbounded medium

Back 4

This is the type of medium wireless communications freely travel across in all directions.

Front 5

current

Back 5

Current is the rate at which electrons flow past a point in a complete electrical circuit.

An amp is used for measuring current expressing the amount of electrons flowing past a point in a circuit over a given time.

Front 6

oscillation

Back 6

Also known as cycling, this is another name for the fluctuation of voltage in an AC current, between positive and negative voltage,

Front 7

propagation behaviors

Back 7

This term is used to describe the variety or combination of movement behaviors of RF electromagnetic signals. This variety or combination includes absorption, reflection, scattering, refraction, diffraction, amplification and attenuation.

Front 8

wavelength

Back 8

The measure of distance in metres between two identical peaks (high points) or troughs (low points) in a RF sine wave

Front 9

frequency

Back 9

Is the amount of full wavelengths of an AC signal that occurs within a 1 second, measured in Hertz (Hz).

Front 10

amplitude

Back 10

The height from the centre line to the peak or positive crests and negative troughs of a waveform.

Represents the signals strength or power.

Front 11

transmit amplitude

Back 11

This is the amplitude of the RF electromagnetic signal when it leaves the Tx of a radio antenna.

Front 12

received amplitude

Back 12

This is the amplitude of the RF electromagnetic signal when it is received at the Rx of a radio antenna.

Front 13

phase

Back 13

This RF characteristic is the relationship between the position of peaks on two RF signals. This can be measured in distance, time, or degrees.

Front 14

out of phase

Back 14

This is used to describe two RF signals with the same frequency and amplitude whose peaks are not in exact alignment.

Front 15

propagation

Back 15

This RF behavior is described as the way in which RF wave moves through the unbounded medium.

Front 16

absorption

Back 16

This is the most common RF behavior, which is when the RF wave does not bounce off an object but absorbed.

This is the leading cause of attenuation.

Front 17

reflection

Back 17

When an RF signal hits a surface and the angle of reflection is equal to the angle of incidence causing the signal bounce off in another direction.

Front 18

scattering

Back 18

When an RF signal hits a surface or multiple surfaces that are smaller than the RF signals' wavelength. Also known as multiple reflections.

Front 19

refraction

Back 19

The bending of an RF signal as it passes through a medium with a different density, cause the direction of the wave to change.

Front 20

diffraction

Back 20

The bending and spreading of an RF signal around an object.

Front 21

RF shadow

Back 21

This is the area directly behind the obstruction causing the diffraction is known as this.

Front 22

attenuation

Back 22

This RF propagation behavior is also know as loss, and is best described as the decrease in amplitude.

Front 23

free space path loss

Back 23

the loss of amplitude (signal strength) caused by the natural broadening of the waves, also referred to as beam divergence.

Front 24

multipath

Back 24

The propagation phenomenon that results in two or more paths of a signal arriving at the receiving antenna at the same time or within nanoseonds of each other.

Front 25

delay spread

Back 25

This is the time difference between the received paths of the same signal at the receiving antenna.

Front 26

gain

Back 26

The relative measurement of an antenna’s ability to direct or concentrate the radiated signal emitting from it.

"ability to amplify a signal"

Front 27

upfade

Back 27

This result of multipath is described as when multiple RF signal paths arrive at receiver in phase, or partially out of phase, causing an increase in amplitude.

Phase differences of 0 to 120 degrees cause this.

Front 28

downfade

Back 28

This result of multipath is described as when multiple RF signal paths arrive at receiver out of phase, causing a decrease in amplitude.

Phase differences between 121 and 179 degrees cause this.

Front 29

nulling

Back 29

This result of multipath is described as when multiple RF signal paths arrive at receiver 180 degrees out of phase, causing a complete cancellation of the RF signal.

Front 30

data corruption

Back 30

This is the most common occurrence of destructive multipath, otherwise known as Intersymbol Interference (ISI), which is when the delay spread differential causes bits to overlap with each other, resulting in this.

Front 31

spectrum analyzer

Back 31

This amplitude measuring tool can be used to measure amplitude of a finite frequency spectrum, otherwise known as a frequency domain tool.

Front 32

oscilloscope

Back 32

This amplitude measuring tool can be used to measure how a signal's amplitude changes over time, otherwise known as a time domain tool.

Front 33

in phase

Back 33

This is used to describe two RF signals with the same frequency and amplitude whose peaks are in exact alignment.

Front 34

transmitter

Back 34

This is the initial component in the creation of the wireless medium. After this receives data from computer, this starts the RF communication.

Front 35

power level

Back 35

In addition to the transmitter generating a signal at a specific frequency, it is also responsible for determining the original transmission amplitude, and is otherwise known as this.

Front 36

EIRP (Equivalent isotropically radiated power)

Back 36

This is the highest RF signal strength (amplitude) that is transmitted from a particular antenna.

Antenna output - adapter cable loss - extension cable loss + antennagain = EIRP

Front 37

absolute (power)

Back 37

Units of power such as watt (W), milliwatt (mW) and dBm (decibels) are units of this type of measurement.

Front 38

dBi (decibels isotropic)

Back 38

measures theantenna’s gain against a true isotropic antenna; a non-existent antenna basedon a perfect omnidirectional radiator.

Front 39

unity-gain

Back 39

An antenna with a dBi value of 0 is often reffered to as a no-gain antenna. Another name for this is...

Front 40

dBd (decibels dipole)

Back 40

This is the gain of an antenna relative to a dipole antenna. A simple dipoleantenna with a gain of 2.15 dBi, actually has the gain of 0 dBd.

Front 41

noise floor

Back 41

This in the ambient or background level of radio energy on a specific channel.

Front 42

SNR (Signal to Noise Ratio)

Back 42

This is the difference in decibels between the received signal and the noise floor.

Front 43

receive sensitivity

Back 43

This refers to the power level of an RF signal required to be successfully received by the receiver radio.

Front 44

RSSI (Received Signal Strength Indicator)

Back 44

Relative, Manufacturer specific metric used to measure received signal strength (amplitude).

Front 45

antenna

Back 45

This piece of hardware is responsible for taking the AC signal from the the transmitter and directs or radiates the RF waves. It will also convert RF waves in the air and directs the AC signal to the reciever.

Front 46

isotropic radiator

Back 46

This is a device that radiates RF energy equally in all directions.

Front 47

receiver

Back 47

This is the final component in the wireless unbounded medium. This component is responsible for taking the carrier signal that is received from the antenna and translates the modulated signal into 0s and 1s.

Front 48

IR (intentional radiator)

Back 48

This is a device with a primary purpose of intentionally generating and emitting RF energy by radiation or induction. The amount of power that is generated by this is regulated by the FCC. The components included in this are the transmitter, all the cables, connectors, and any other equipment, not including the antenna.

Front 49

relative (power)

Back 49

Units of comparison such as dB(decibel), dBi (decibels isotropic) and dBd (decibels dipole) are units of this type of measurement.

Front 50

W (watt)

Back 50

This basic unit of power is equal to 1 ampere (amp) of current flowing at 1 volt (V).

Front 51

mW (milliwatt)

Back 51

This basic unit of power is equal to 1/1,000 of a watt.

Front 52

dB (decibel)

Back 52

dB is a unit to measure power ratio or gain for comparison of antennas

Front 53

Mega

Back 53

M --> 10^6

Front 54

Kilo

Back 54

k --> 10^3

Front 55

Deci

Back 55

d --> 10^(-1)

Front 56

Centi

Back 56

c --> 10^(-2)

Front 57

Milli

Back 57

m --> 10^(-3)

Front 58

Micro

Back 58

u (mu) --> 10^(-6)

Front 59

nano

Back 59

n --> 10^(-9)

Front 60

pico

Back 60

p --> 10^(-12)

Front 61

Giga

Back 61

G 10^(9)

Front 62

HF range

Back 62

3 to 30MHz

Front 63

VHF range

Back 63

30 to 300MHz

Front 64

UHF range

Back 64

300 to 3000MHz

Front 65

Length of 1/2 wave for 10MHz

Back 65

15m

Front 66

Length of full wave for 30MHz

Back 66

10m

Front 67

Length of full wave at 300MHz

Back 67

1m

Front 68

Length of half wave at 3GHz

Back 68

5cm

Front 69

HF primary propagation

Back 69

Skywave

Front 70

VHF and UHF inside Fresnel zone propagation

Back 70

Direct wave

Front 71

Dipole

Back 71

Omni directional

Low or no gain

1/2 or 1/4 wave generally

Linearly polarised (Hori or vert)

Single freq

Front 72

Yagi

Back 72

Direction

High gain

1/2 or 1/4 wavelength

Dipole with parasitic elms (reflector & directors)

Linearly polarised

Front 73

LPA

Back 73

Directional

Moderate gain (less gain than Yagi)

1/2 or 1/4 wavelength per band

Wideband or multiband, but reduced gain to that of Yagi

Linearly polarised

Elm spacing decreases towards the front of the array where they are the smallest

Front 74

Discone

Back 74

Omni directional

low gain

Antenna size dependant on lowest freq needed

Extremely wideband/multi band

linearly polarized

Cover huge bands at reduced sensitivity compared to dipole

Front 75

Monopol

Back 75

Omni directional

low or no gain

1/4 wave

single freq

Vert polarised

Less effective than dipole

Uses a ground plane

Front 76

Parabolic dish

Back 76

extremely directional

very high gain

size of dish determines gain

single freq or broadband

circulary polarised

Back 77

1MHz = 300m

10MHz = 30m

50MHz = 6m

100MHz = 3m

300MHz = 1m

500MHz = 0.6m

800MHz = 37.5cm

900MHz = 33.3cm

1GHz = 30cm

Front 78

wavelength= velocity / freq

Back 78

wavelength = 300 x 10^6 / freq x 10^6

Front 79

30db gain ratio

Back 79

1000:1

Front 80

10db gain ratio

Back 80

10:1

Front 81

20db gain ratio

Back 81

100:1

Front 82

23db gain ratio

Back 82

200:1

Front 83

26db gain ratio

Back 83

400:1

Front 84

29db gain ratio

Back 84

800:1

Front 85

0 db gain ratio

Back 85

1:1

Front 86

3db gain ratio

Back 86

2:1

Front 87

6db gain ratio

Back 87

4:1

Front 88

Free space path loss

Back 88

The loss between two isotropic radiators in free space, expressed as a power ratio.

Front 89

Cable Loss

Back 89

Signal power degradation that occurs in the feed line, measured in decibels per unit length, at a given freq.

Depends on theproperties of the transmission lines & variables like freq, cable type and length.

In the case of a coaxial cable, higher frequencies have greater loss than lower frequencies. As an example, gold wires will have lowerline loss than copper lines.

Front 90

Inductance

Back 90

Electromagnetic induction affects feedlines bypotentially interfering with the signals being carried.

The induction occurswhen an electromagnetic source is in proximity and the signal attenuates on thefeedline.

Front 91

Capacitance

Back 91

Is the ability of a body i.e. cable to hold anelectrical charge. It is also a measureof the amount of electric charge stored.

Cables have a limited capacitance, kinks add to this

Front 92

Shielding

Back 92

The shieldingeffectiveness of a feedline is the rating for how much the RF shielding reducessignal interference.

Front 93

dBm

Back 93

is a measure ofsignal power. A dBm is a standard unit for measuring levels of power inrelation to a 1 milliwatt (mW) reference signal.

Front 94

VSWR (Voltage Standing Wave Ratio)

Back 94

describes the effectiveness of transferring power from thefeedline to the antenna.

It allows us to measure how much energy an antenna isable to successfully convert to RF when transmitting, and how much energy itleaves behind on the feed line.

Lower=more efficient

Front 95

Input Power

Back 95

The maximum power that the antenna can transmit or receive.

Usually, themaximum input power is rated in Watts. If this maximum is exceeded, damage tothe antenna, feedlines, and transceivers will likely occur.

Front 96

Beam width

Back 96

The beam width of anantenna is the vertical and horizontal RF coverage area expressed in degrees.Beam width is associated with directional antennas. It is also referred to asthe propagation pattern.

Front 97

Antenna Diversity

Back 97

Using two or morereceiving antennas on a wireless device can be used to eliminate multipathsignal distortion.

Typically, the signal from the antenna with the least noise(best Signal-Noise Ratio, SNR) is chosen, and the other antenna(s) is ignored.

Front 98

2m band

Back 98

2m Band – CB radio system, requires a licence to operate in the US and uses frequenciesin the VHF range between 140 – 144MHz.

Front 99

FRS (Family Radio Service)

Back 99

UHF Band improved civilian radio system most commonlyreferred to as the FRS band in the US. It uses channelized frequencies between 462 – 467MHz which is partlyshares with the GMRS.

Front 100

GMRS - (General Mobile Radio Service)

Back 100

Short range VHF civilian communications bandthat requires a licence to operate in the US. 462.550 - 462.725

Front 101

MURS - (Multi Use Radio Service)

Back 101

an unlicensed two way radio servicewith a power limit of 2 Watts that provides a private, two-way, short distancevoice or data communications service.

151.820 - 154.600