The link budget
For each link a 'link budget' needs to be made. The link budget will calculate the signal level through the link, and predicts the signal level at the receiver's side. Within the 'link budget' there are a few parameters that are influenced by the location of the link. These are humidity and terrain roughness. The length of the link has also got a major influence on the 'link budget'.
You might like to consider the link in three stages:
1. The transmitting end consisting of the transmitter (e.g. access point), the antenna cable and the antenna.
2. The middle bit; you know, the air in between the two sites.
3. The receiving end i.e. the receiver (e.g. access point), the antenna cable and the antenna.
The link budget calculation is as follows:
Transmitter Air Receiver
Pout Output power of transmitter in dbm
Ct Antenna and cable losses at transmitter in dB
Gt Transmitter Antenna gain in dbi
FSL 'Free Space Loss', propagation loss in dB (negative number)
Cr Antenna and cable losses at receiver in dB
Gr Receiver Antenna gain in dbi
Rin Receiver sensitivity in dbm (negative number)
Download our link budget spreadsheet