Link Budget Calculator
Walk from transmitter to receiver with editable gains, losses, sensitivity, and margin.
- Typical inputs
- Transmit level, feed losses, antenna gains, path loss, receiver sensitivity, and reserve.
- Calculated output
- Reference-plane ledger, receive level, conditional sensitivity, margin, and pass/fail indication.
- Model status
- Release B · documented and numerically tested
Which reference-plane term controls the final receive margin?
Auditable reference-plane ledger
Add, remove, and reorder named gains or loss magnitudes. Transmit-side rows occur before path loss; receive-side rows occur after it.
| Row | Plane | Type | dB | Order |
|---|---|---|---|---|
10.00 dBmTransmit feed
8.00 dBmTransmit antenna
11.00 dBmPolarization / system
11.00 dBmFree-space path loss
-69.23 dBmReceive antenna
-66.23 dBmReceive feed
-67.23 dBm
| Reference plane / term | Signed change | Level |
|---|---|---|
| Transmitter output | start | 10.0000 dBm |
| Transmit feed | -2.0000 dB | 8.0000 dBm |
| Transmit antenna | +3.0000 dB | 11.0000 dBm |
| Polarization / system | +0.0000 dB | 11.0000 dBm |
| Free-space path loss | -80.2311 dB | -69.2311 dBm |
| Receive antenna | +3.0000 dB | -66.2311 dBm |
| Receive feed | -1.0000 dB | -67.2311 dBm |
- Path loss
- 80.2311 dB
- Received power
- 189.186 pW
- Sensitivity
- -95.0000 dBm
- Reserve
- 3.000 dB
- Conditional decision
- Pass
Deterministic margin is not statistical availability and is not a range claim. Add each fade, body, rain, foliage, connector, polarization, or implementation term explicitly when justified.
What this calculator is doing
The ledger advances left to right: absolute dBm starts the chain, dB gains add, and losses entered as positive magnitudes subtract. Margin is receive level minus sensitivity and reserve.
How to read the result
A positive margin passes only the entered assumptions. Reliability still depends on fading, body loss, obstruction, tolerances, and applicable constraints.
Equations & conventions
- Absolute powers are in dBm; gains and loss magnitudes are in dB.
- Sensitivity is the minimum input level for the entered criterion.
- Reserve is subtracted from raw receive margin.
Independently checked example
Checked default: 10 dBm, 2 dB TX loss, 3 dBi TX gain, 80.2311 dB FSPL, 3 dBi RX gain, and 1 dB RX loss produces −67.2311 dBm; against −95 dBm with 3 dB reserve, margin is 24.7689 dB.
Common mistakes
- Adding a positive loss magnitude.
- Combining values from different connector or antenna reference planes.
Assumptions, validity & omissions
- All ledger entries refer to compatible power quantities.
- Manual and calculated path loss are mutually exclusive.
- Fade and implementation margins must be entered explicitly.
Sources & model provenance
- Recommendation ITU-R P.525-5 (11/2024) (opens in a new tab) — In-force free-space attenuation model. Accessed 2026-09-05.
- Keysight, Fundamentals of RF and Microwave Noise Figure Measurements (opens in a new tab) — Noise factor, mismatch, and cascade practice. Accessed 2026-09-05.