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AirborneDirect™ Users Guide Quatech, Inc.
100-8510-110 2/21/2011 31
Link Margin provides a measure of all the parts of the RF path that impact the
ability of two systems to communicate. The basic equation looks like this:
EIRP (dB) = TxP + TxA – TxC
Link Margin (dB) = EIRP – FPL + (RxS + RxA – RxC)
Where: TxP = Transmitter output power (dBm)
TxA = Transmitter antenna gain (dBi)
TxC = Transmitter to Antenna coax cable loss (dB)
FPL = Free Path Loss (dB)
RxS = Receiver receive sensitivity (dBm)
RxA = Receiver antenna gain (dBi)
RxC = Receiver to Antenna coax cable loss (dB)
This is a complex subject and requires more information than is presented here,
Quatech recommends at reviewing the subject and evaluating any system at a
basic level.
It is then possible, with a combination of the above items and an understanding
of the application demands, to achieve a link quality optimized for the application
and host design. It is important to note that this is established with a combination
of hardware selection, design choices and configuration of the radio.