User's Manual

PMP 450 Planning Guide
Link planning
pmp-0047 (June 2013)
2-19
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.
Calculating Link Loss
The link loss is the total attenuation of the wireless signal between two point-to-multipoint units. The link loss
calculation is presented below:
Link Loss (dB) = Transmit power of the remote wireless unit (dBm) − Tx Cable loss (dB) − Received power
at the local unit (dBm) – Rx cable loss (dB) + Antenna gain at the remote unit (dBi) + Antenna gain at the
local unit (dBi)
Calculating Rx Signal Level
The Rx sensitivity of each module is provided at http://www.cambiumnetworks.com. The determinants in Rx signal
level are illustrated in Figure 11.
Figure 11 Determinants in Rx signal level
Rx signal level is calculated as follows:
Rx signal level dB = Tx power − Tx cable loss + Tx antenna gain
− free space path loss + Rx antenna gain − Rx cable loss
This Rx signal level calculation presumes that a clear line of sight is established between the transmitter and
receiver and that no objects encroach in the Fresnel zone.