Link Budget Calculator
Calculate received power, path loss, and link margin for wireless communication links
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Find Max Distance
Find Required Tx Power
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Common Scenarios
Received Power (Prx)
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Free Space Path Loss
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Link Margin
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Status
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Link Budget Fundamentals
Prx = Ptx + Gtx + Grx – Lpath – Lmisc
Free Space Path Loss (FSPL): 20·log10(d) + 20·log10(f) + 32.44 (d in km, f in MHz)
Received Power (Prx): in dBm (or dBW)
Link Margin: Prx – Psens (positive margin = reliable link)
Additional Losses: feeder loss, polarization loss, etc. (dB)
People Also Ask
📡 What is a link budget and why is it important?
A link budget accounts for all gains and losses in a communication system to ensure received power exceeds receiver sensitivity, providing a reliable link.
📏 How do I calculate free space path loss?
FSPL (dB) = 20·log10(d) + 20·log10(f) + 32.44, with d in km and f in MHz. For d in km, f in GHz, use +92.45.
⚖️ What is a good link margin?
Typically 10–20 dB for reliable links under normal conditions. Fade margin accounts for signal fluctuations due to rain, multipath, etc.
📊 How does frequency affect link budget?
Higher frequency increases path loss (log dependence) but allows smaller antennas. Atmospheric absorption also increases at certain bands (e.g., 60 GHz).
📐 What are typical antenna gains for different applications?
Omni: 0–3 dBi, patch: 6–9 dBi, parabolic dish: 20–40 dBi, Yagi: 10–15 dBi.
🔧 How do I convert between dBm and Watts?
P(dBm) = 10·log10(P(W) / 1mW). 1 mW = 0 dBm, 1 W = 30 dBm.
Understanding Link Budget
A link budget sums all power gains and losses from transmitter to receiver. The result, received power (Prx), must be above the receiver’s sensitivity to close the link. The difference is the link margin – a safety buffer against fading and interference.
Key Components
- Transmit Power (Ptx): output of the transmitter (dBm or W).
- Antenna Gains (Gtx, Grx): directivity relative to isotropic radiator (dBi).
- Free Space Path Loss (FSPL): attenuation due to distance and frequency.
- Additional Losses: cable losses, connector loss, polarization mismatch, atmospheric absorption, etc.
- Receiver Sensitivity: minimum input power for required BER/SNR.
Link budget analysis is fundamental in designing any wireless system – from Wi‑Fi to deep‑space communication.
Typical Link Budget Values
| Application | Frequency | Distance | Tx Power | Rx Sensitivity | Typical Margin |
|---|---|---|---|---|---|
| Wi‑Fi 2.4 GHz | 2.4 GHz | 100 m | 20 dBm | -80 dBm | 10–15 dB |
| Satellite downlink (C‑band) | 4 GHz | 36,000 km | 20 W (43 dBm) | -90 dBm | 3–6 dB |
| Microwave backhaul | 18 GHz | 10 km | 10 dBm | -70 dBm | 20 dB |
Frequently Asked Questions
What is the difference between dBm and dBW?
dBm is power relative to 1 milliwatt (0 dBm = 1 mW). dBW is relative to 1 watt (0 dBW = 30 dBm). Conversion: dBW = dBm – 30.
How do I account for rain fade?
Rain fade adds extra attenuation, especially above 10 GHz. Use regional rain zone maps and ITU‑R models to estimate additional loss and include it in the link budget as an extra margin.
Can I use this calculator for non‑line‑of‑sight links?
The basic free‑space model assumes line‑of‑sight. For non‑LOS, additional propagation models (e.g., Okumura‑Hata, COST‑231) are needed. This calculator gives an ideal upper bound.