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Vocabulary
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Some
terms that will be used and their definitions :
- dB
- Decibel, a logarithmic
unit of intensity used to indicated power lost
or gained between two signals. Named after Alexander
Graham Bell.
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- dBd
- Gain in decibels
referenced to a standard half-wave dipole antenna. This
is a more realistic reference to antenna gain.
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- dBi
- Gain in decibels
referenced to an isotropic radiator. An isotropic
radiator is a theoretical antenna with equal gain to all
points on isotropic sphere. 2.15 dBi = 0 dBd
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- dBadv
- Meaningless random large
numbers generated by advertising departments.
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- dBm
- Decibel referenced to 1
milliwatt into a 50 Ohm impedance (usually) 0 dBm
= 1 mW
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- kBps
- Kilobytes per second,
unit of data rate measurement, 1,000 bytes per second or
8,000 bits per second. Example: 30 kBps
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- kHz
- Kilohertz, unit of
frequency measurement, 1,000 periods per second. Example:
455 kHz
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- kbps
- Kilobits per second,
unit of data rate measurement, 1,000 bits per second. Example:
128 kbps
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- mW
- Milliwatt, one
thousandth (1/1000) of a Watt, used to indicate
received or transmitted power.
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- DSSS
- Direct Sequence Spread
Spectrum, a RF carrier and pseudo-random pulse train are
mixed to make a noise like wide-band signal.
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- EIRP
- Effective Isotropic
Radiated Power, actual power transmitted in the main
lobe after taking in account all cable losses and
antenna gain. Based on an isotropic antenna.
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- FHSS
- Frequency Hopping Spread
Spectrum, transmitting on one frequency for a certain
time, then randomly jumping to another, and transmitting
again.
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- FSK
- Frequency Shift Keying,
modulating a transmitter by using data signals to shift
the carrier frequency. Commonly used for digital
communications.
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- GHz
- Gigahertz, unit of
frequency measurement, 1,000,000,000 periods per
second. Example: 2.4 GHz
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- Hz
- Hertz, the basic unit of
frequency measurement, cycle per second. Example:
60 Hz
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- MHz
- Megahertz, unit of
frequency measurement, 1,000,000 periods per second. Example:
147.075 MHz
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- MMDS
- Multichannel Multipoint
Distribution Service, wireless method of remotely
sending conventional cable TV service to rural areas or
over long distances using microwave radio frequencies.
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- Mbps
- Megabits per second,
unit of data rate measurement, 1,000,000 bits per
second. Example: 1.544 Mbps
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- RF
- Radio Frequency,
electromagnetic radiation between 10 kHz and 300 GHz.
-
- Bandwidth
- The width of a signal on
the radio spectrum. The greater the signal's bandwidth,
the more frequency space it occupies, and the stronger
the signal needs to be to overcome noise.
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- Coaxial Cable
- A type of wire in which
a center conductor is surrounded by a concentric outer
conductor. Also called "coax".
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- Fade Margin
- Fade margin is the
difference, in dB, between the magnitude of the received
signal at the receiver input and the minimum level of
signal determined for reliable operation. Higher the
fade margin, the more reliable the link will be. The
exact amount of fade margin required depends on the
desired reliability of the link, but a good
rule-of-thumb is 20 to 30 dB. Fade margin is often
referred to as "thermal" or "system operating margin".
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- Front-To-Rear (Back)
Ratio
- Antenna measurement that
is determined from the peak power difference, in
decibels, between the main radiation lobe at 0°
(front of an antenna) and the strongest rearward lobe
(back of the antenna). Higher the ratio, the more
directional the antenna is.
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- Free Space Loss
- Attenuation, in dB, of a
RF signal's power as it propagates through open space.
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- Fresnel Zone
- The Fresnel (fre'-nel)
zone is an elliptical region surrounding the
line-of-sight path between transmitting and receive
antennas. Must be obstruction free for a microwave
radio link to work properly.
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- Impedance
- The complex combination
of resistance and reactance, measured in Ohms (50
typically). Impedance must be matched for maximum power
transfer.
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- Isotropic
- Hypothetical, lossless
electromagnetic wave radiating equally in all directions
from a point source in free space. Used as a reference
for antenna gain.
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- Line-of-Sight
- When the transmit and
receive antennas can physically see each other.
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- Multipath
- When the RF signal
arrives at the receiving antenna after bouncing through
several paths. Significantly degrades the received
signal power.
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- Path Loss
- Free space loss of RF
power plus any power loss due to link path obstructions,
poor antenna height, and link distance.
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- Polarization
- The polarity of a radio
signal's electric field. Transmit and receive antennas
must have the same polarity for maximum receive power.
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- Radiation Fields
- There are three
traditional radiation fields in free space as a result
of an antenna radiating power.
 | Near-field,
also called the reactive near-field region, is the
region that is closest to the transmitting antenna and
for which the reactive field dominates over the
radiative fields. |
| Fresnel zone,
also called the radiating near-field, is that region
between the reactive near-field and the far-field
regions and is the region in which the radiation
fields dominate and where the angular field
distribution depends on distance from the transmitting
antenna. |
| Far-field, or
Rayleigh distance, is the region where the radiation
pattern is independent of distance from the
transmitting antenna. |
Receiver Sensitivity
The minimum required RF
signal power received to meet are certain performance
level. This level is usually referred to as the Bit
Error Rate (BER). Example: -80 dBm or 0.000000010 mW
Wuss
When your bunghole
friend won't answer the radio, send the cops to his work
to tell him to turn on the HT so in all your pinkness,
you don't buy the wrong computer hardware, again. Also
people who transmit in mono.
Yagi
A directional antenna
made up of one driven element and one, or more,
parasitic elements.
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