Military utility tools / Radio link budget
Radio link budget
Power, gains, losses, frequency and range in. Received level and fade margin out.
Set the inputs, then work it out.
Transmit power--dBm
EIRP--dBm
Path loss--dB free space
Received level--dBm
Fade margin--dB above sensitivity
Verdict--—
Received power--picowatts
Max range--km at 0 dB margin
What fade margin should I aim for?
Ten decibels is a working minimum and twenty is what you want on a link that has to stay up. Free space is the best case, so anything close to zero here will not work on real ground.
Why does doubling the distance cost six decibels?
Path loss goes with the square of distance, and a factor of four in power is six decibels. The same six decibels applies to doubling frequency, which is why higher bands need more gain over the same path.