Link Budget
Prx = Ptx + Gtx − Ltx − FSPL + Grx − Lrx
Quick answer
This calculator solves Prx = Ptx + Gtx - Ltx - FSPL + Grx - Lrx for Prx. With Tx Power (dBm) 0 dBm, Tx Gain (dBi) 9 dBi, Tx Loss (dB) 20 dB, Path Loss (dB) 44 dB, Rx Gain (dBi) 19.8 dBi, Rx Loss (dB) 94 dB, the result is -129.2 dBm.
Calculator
Formula
Description
A link budget accounts for all gains and losses in a wireless communication link to determine whether the received signal power is sufficient for reliable operation. Starting with the transmitter power, antenna gains add signal strength by focusing energy in a particular direction, while cable losses and free space path loss subtract from it. The result must exceed the receiver's sensitivity threshold by a fade margin (typically 10-20 dB) to ensure reliable operation under varying conditions such as rain, multipath, and interference.
Variables
- Prx — Received power (dBm)
- Ptx — Transmitter output power (dBm)
- Gtx — Transmit antenna gain (dBi)
- Ltx — Transmitter cable/connector losses (dB)
- FSPL — Free space path loss (dB)
- Grx — Receive antenna gain (dBi)
- Lrx — Receiver cable/connector losses (dB)
Practical Notes
Receiver sensitivity for common systems: WiFi -65 to -85 dBm, Bluetooth -70 to -90 dBm, LoRa -130 to -148 dBm, cellular LTE -100 to -120 dBm. Always include a fade margin of at least 10 dB for outdoor links and 20 dB for indoor or obstructed paths.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Ptx | Tx Power (dBm) | dBm | dBm |
| Gtx | Tx Gain (dBi) | dBi | dBi |
| Ltx | Tx Loss (dB) | dB | dB |
| FSPL | Path Loss (dB) | dB | dB |
| Grx | Rx Gain (dBi) | dBi | dBi |
| Lrx | Rx Loss (dB) | dB | dB |
Step by step
- 1. What you know: Tx Power (dBm) 0 dBm, Tx Gain (dBi) 9 dBi, Tx Loss (dB) 20 dB, Path Loss (dB) 44 dB, Rx Gain (dBi) 19.8 dBi, Rx Loss (dB) 94 dB
- 2. The relation: Prx = Ptx + Gtx - Ltx - FSPL + Grx - Lrx
- 3. Substitute: Ptx = 0 dBm, Gtx = 9 dBi, Ltx = 20 dB, FSPL = 44 dB, Grx = 19.8 dBi, Lrx = 94 dB
- 4. Result: Prx = -129.2 dBm
Worked examples
Minimum range
Given: Tx Power (dBm) -2 dBm, Tx Gain (dBi) 0.2 dBi, Tx Loss (dB) 0.3 dB, Path Loss (dB) 0.66 dB, Rx Gain (dBi) 0.44 dBi, Rx Loss (dB) 1.41 dB
Result: Prx = -3.73 dBm
Low range
Given: Tx Power (dBm) -20 dBm, Tx Gain (dBi) 2 dBi, Tx Loss (dB) 3 dB, Path Loss (dB) 6.6 dB, Rx Gain (dBi) 4.4 dBi, Rx Loss (dB) 14.1 dB
Result: Prx = -37.3 dBm
Typical
Given: Tx Power (dBm) 0 dBm, Tx Gain (dBi) 9 dBi, Tx Loss (dB) 20 dB, Path Loss (dB) 44 dB, Rx Gain (dBi) 19.8 dBi, Rx Loss (dB) 94 dB
Result: Prx = -129.2 dBm
High range
Given: Tx Power (dBm) 30 dBm, Tx Gain (dBi) 20 dBi, Tx Loss (dB) 60 dB, Path Loss (dB) 132 dB, Rx Gain (dBi) 44 dBi, Rx Loss (dB) 282 dB
Result: Prx = -380 dBm
Maximum range
Given: Tx Power (dBm) 300 dBm, Tx Gain (dBi) 200 dBi, Tx Loss (dB) 600 dB, Path Loss (dB) 1320 dB, Rx Gain (dBi) 440 dBi, Rx Loss (dB) 2820 dB
Result: Prx = -3800 dBm
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<p><a href="https://vbatpower.com/formulas/link-budget/">Link Budget</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Link Budget?
Use Prx = Ptx + Gtx - Ltx - FSPL + Grx - Lrx. With Tx Power (dBm) 0 dBm, Tx Gain (dBi) 9 dBi, Tx Loss (dB) 20 dB, Path Loss (dB) 44 dB, Rx Gain (dBi) 19.8 dBi, Rx Loss (dB) 94 dB, Prx works out to -129.2 dBm.
What is the formula for Link Budget?
The formula is Prx = Ptx + Gtx - Ltx - FSPL + Grx - Lrx. A link budget accounts for all gains and losses in a wireless communication link to determine whether the received signal power is sufficient for reliable operation.
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