Intentional Radiators
This is the RF device
used for generating and transmitting RF signals. Intentional radiators (IR) include the
following
-
RF Device
-
Cables
-
Connectors
All of these except the antenna make up an
intentional Radiator
Equivalent
isotropically radiated power (EIRP): this is the actual output by the antenna
element.
RF MATHS
Rules.
1. + 3db gain= Doubles the power in MW (×2)
2. - 3db loss = half of the power in MW (
)
)
3. – 10db loss = 
of the power in MW ( )
of the power in MW ( )
4. +10db gain in= 10 times to the power in MW (x10)
Example: GAIN 100MW + 3db = 200MW
30MW+ 3db = 60MW
i e 100MWx=200MW and 30MWx
2 = 60MW for every 3db gain in power
Also
100MW + 6dB =
100MWx4=400MW 40MW +3dB +3dB+3dB =
40mw + (2x2x2) db =
40MW+8db = 40mw x 8 =320mw
Loss in RF power
Example
40mw + 3db +3db – 3db
=40mw + 3db = 40mw x 2= 80mw.
40mw – 10db = 40mw x 
=4mw
=4mw
Exercise
1.
40mw +10db +10db
2.
12mw + 16db
Answer
1.
40mw + 10db + 10db =
40mw x 10 x 10 =4000mw
2.
12mw +16db =12mw
+10db+3db +3db = 12mw x 10x4 =12mw x 40 =480mw
SIGNAL TO NOISE RATIO (SNR)
Back RF noise which can be cause by
various system and natural phenomena that generate energy in electromagnetic
spectrum is known as Noise Floor. The power level of the RF signal in
relative to the power level of the noise floor is known as signal to noise
ratio.
Received
signal strength indicator (RSSI). RSSI has a range of 0-255 while cisco
uses 0-100. The RSSI is an arbitrary measurement of received signal strength
defined in IEEE 802.11 standard (These are the signal bar in your phone or RF device
like Access point (AP) or Router)
Effective Radiated power (ERP).
ERP
has a power of 0 dbi (zero dbi). ERP is the radiated power from a half – wave
di-pole. The radiated power from an isotropic source is given by:
EIRP = ERP+2.14db
QUESTION
A
transmitter with an output power of 100mw transmits signal and incur a loss of
-3dbi before reaching an antenna with a power of +10dbi.