Trango Broadband Access5830 - Manual (Page 72)

Management
Trango Broadband Wireless — Access5830 User Manual Rev. F page 68
Directional Antenna
Radiates and receives most of the signal power in one direction. The following diagram shows the radiation pattern of a
directional antenna with its side lobes in polar form.
Figure 9-3: Radiation Pattern of Directional Antenna
Antenna Beamwidth
It is a common figure of merit used to define the angle between two half-power (-3 dB) points on either side of the main lobe of
radiation.
Receiver Sensitivity
Receiver sensitivity is defined as the minimum RF signal power level required at the input of a receiver for
certain performance (i.e. BER).
EIRP
EIRP (Effective Isotropic Radiated Power) is defined as the antenna transmitted power that is equal to the
transmitted output power minus cable-loss plus the transmitting antenna gain.
Pout = Output power of transmitter expressed in dBm
Ct = Transmitter cable attenuation in dB
Gt = Transmitting antenna gain in dBi
Gr = Receiving antenna gain in dBi
Pl = Path loss in dB
Cr = Receiver cable attenuation is dB
Si = Received power level at receiver input in dBm
Ps = Receiver sensitivity in dBm
Si = Pout - Ct + Gt - Pl + Gr - Cr
EIRP = Pout - Ct + Gt
Link Budget Example:
Link Parameters:
Frequency: 5.8 GHz
Pout = 4 dBm (2.5 mW)
Tx and Rx cable length (Ct and Cr) = 10 m. cable type RG214 (0.6 dB/meter)
Tx and Rx antenna gain (Gt and Gr) = 17 dBi
Distance between sites = 3 Km
Receiver sensitivity (Ps) = -85 dBm
Link Budget Calculation:
EIRP = Pout - Ct + Gt = 16 dBm
Pl = 32.4 + 20xLog(FMHz) + 20xLog(RKm) 117 dB
Si = EIRP - Pl + Gr - Cr = -79 dBm
In this example the received signal power is above the sensitivity threshold, so the link should work. The problem is that there
is only a 6 dB difference between received signal power and sensitivity. Normally a higher margin is desirable due to
fluctuation in the received power as a result of signal fading.