RF · link design
Link budget calculator.
Add up power, gains and losses to get received level, fade margin and the longest free-space range.
Inputs
Link result
Enter values to calculate.
How do I calculate a link budget?
A link budget adds every gain and subtracts every loss between the transmitter and the receiver: received power = transmit power - transmitter cable loss + transmit antenna gain - path loss + receive antenna gain - receiver cable loss - other losses. The fade margin is received power minus the receiver sensitivity, the cushion left for fading and interference. Path loss here is free-space loss from ITU-R P.525.
Worked example. 20 dBm transmit power, 3 dBi antennas on both ends, 1 dB cable loss each side, 2.4 GHz, 1 km, sensitivity -90 dBm: received power is -76.1 dBm and the fade margin is 13.9 dB. Keeping 10 dB of margin, the free-space range is 1.6 km; with zero margin it is 5 km.
Free-space range is an upper bound. Take sensitivity, antenna gain and cable loss from your own datasheets; this page does not supply typical values.
Frequently asked questions
What is fade margin?
Received power minus receiver sensitivity, in dB. It is the signal drop the link can absorb before it stops working.
How much fade margin do I need?
That depends on the link and its required reliability; this tool lets you enter your own target and does not set one.
Where do I find receiver sensitivity?
In the radio or module datasheet. It changes with data rate, so use the value for the rate you will run.
Why is real range shorter than the result?
The range here assumes free space. Obstructions, ground reflection and interference reduce it.
Sources
Checked
Gains and losses are user inputs from datasheets. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Free-space estimate only. Not a coverage study or a regulatory compliance check.