RF Link Budget Calculator

Calculate received signal power and link margin for a wireless communication link.

What is a link budget?

Like planning a road trip budget — you start with a full tank of gas (transmit power), gain fuel at stops (antenna gains), and lose fuel on hills (path loss and cable losses). A link budget tells you whether your signal will "make it" to the receiver.

Why does this matter?

Satellite engineers calculate link budgets to ensure signals traveling hundreds of millions of kilometers from deep space probes still reach Earth with enough power to decode. The same principle applies to your WiFi router, a cell tower, or a drone's control link.

Transmitter
TX power output and antenna gain.
dBm

How strong the transmitter broadcasts. Typical values: 0 dBm (1 mW), 20 dBm (100 mW), 30 dBm (1 W), 43 dBm (20 W)

dBi

How much the antenna focuses power in a direction compared to a perfect sphere. A directional dish has much higher gain than a simple whip. Dipole ≈ 2.15 dBi

Receiver
RX antenna gain and minimum sensitivity threshold.
dBi

How well the receiving antenna collects the incoming signal. Higher gain = better at picking up weak signals from a specific direction.

dBm

The weakest signal the receiver can still decode. More negative = more sensitive. Typical: −90 to −120 dBm for low-power receivers.

Path Parameters
Frequency, distance, and additional losses.
MHz

Higher frequencies lose more signal over distance. 915 MHz is a common IoT band.

km

Straight-line distance between transmitter and receiver.

dB

Cable losses, connector losses, atmospheric attenuation, building penetration, etc.

Link Budget Cascade
Power accounting from transmitter to receiver.
+TX Power
20dBm
+TX Antenna Gain
3dBi
EIRP = 23.00 dBm
+RX Antenna Gain
3dBi
-Free Space Path Loss (915MHz, 10km)
111.67dB
-Additional Losses
2dB
=Received Power
-87.67 dBm
Receiver Sensitivity
-100 dBm
Link Margin+12.3dB
Link is viableReceived power exceeds sensitivity by 12.3 dB.

A link margin of 10–20 dB is recommended to account for fading, interference, and environmental variations. Safety-critical links should target ≥ 20 dB margin.