Cambium PTP 450 series, Руководство пользователя

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Link planning PTP 450 User Guide
ptp-450 (July 2014)
2-57
Path loss considerations
Path loss is the amount of attenuation the radio signal undergoes between the two ends of the link.
Calculating path loss
The path loss is the sum of the attenuation of the path if there were no obstacles in the way (Free Space Path Loss),
the attenuation caused by obstacles (Excess Path Loss) and a margin to allow for possible fading of the radio signal
(Fade Margin). The following calculation needs to be performed to judge whether a particular link can be installed:
capability seasonal fade excess space free
L L L L L
   
_
Where: Is:
space free
L
_
Free Space Path Loss (dB)
excess
L
Excess Path Loss (dB)
fade
L
Fade Margin Required (dB)
seasonal
L
Seasonal Fading (dB)
capability
L
Equipment Capability (dB)
Calculating maximum power level for connectorized units
If a connectorized PTP 450 BHM or BHS is to be installed in a country that imposes an EIRP limit in the selected
band, calculate the highest setting of Maximum Power Level that will be permitted using this formula:
Maximum Power Level (dBm) = Allowed EIRP (dBm) – Antenna Gain (dBi) + Cable Loss (dB)
Where: Is:
Maximum Power
Level (dBm)
the highest permissible setting of the transmitter
output power,
Allowed EIRP (dBm) the EIRP limit allowed by the regulations,
Antenna Gain (dBi) the gain of the chosen antenna,
Cable Loss (dB) the loss of the RF cable connecting the BHM or BHS
to the antenna.
For more information on EIRP limits, see Compliance with radio regulations on page 4-124 .
Understanding Attenuation
An RF signal in space is attenuated by atmospheric and other effects as a function of the distance from the initial
transmission point. The further a reception point is placed from the transmission point, the weaker is the received
RF signal.