Link Budget Calculator Formula

Understand the math behind the link budget calculator. Each variable explained with a worked example.

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Formulas Used

Received Power

rx_power = received_power

Link Margin

link_margin = received_power - rx_sensitivity_dbm

Link Viable?

link_closes = received_power > rx_sensitivity_dbm ? 1 : 0

Variables

VariableDescriptionDefault
tx_power_dbmTransmit Power(dBm)30
tx_antenna_gainTX Antenna Gain(dBi)15
rx_antenna_gainRX Antenna Gain(dBi)15
path_loss_dbTotal Path Loss(dB)120
misc_losses_dbMisc Losses (cables, connectors)(dB)3
rx_sensitivity_dbmReceiver Sensitivity(dBm)-90
received_powerDerived value= tx_power_dbm + tx_antenna_gain + rx_antenna_gain - path_loss_db - misc_losses_dbcalculated

How It Works

How a Link Budget Works

A link budget adds up all gains and subtracts all losses between transmitter and receiver to find the received power.

Formula

P_rx = P_tx + G_tx + G_rx - L_path - L_misc

Link Margin = P_rx - Receiver Sensitivity

A positive link margin means the link will work. Engineers typically design for 10-20 dB of margin to account for fading and environmental variation.

Worked Example

30 dBm transmitter, 15 dBi antennas on each end, 120 dB path loss, 3 dB misc losses, receiver sensitivity -90 dBm.

tx_power_dbm = 30tx_antenna_gain = 15rx_antenna_gain = 15path_loss_db = 120misc_losses_db = 3rx_sensitivity_dbm = -90
  1. 01Received power: 30 + 15 + 15 - 120 - 3 = -63 dBm
  2. 02Link margin: -63 - (-90) = 27 dB
  3. 03Link is viable with 27 dB margin

Ready to run the numbers?

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