What Is the Free-Space Path Loss (FSPL) & RF Link Budget Calculator?
Free-space path loss (FSPL) is the attenuation of radio energy resulting from a strictly unobstructed line-of-sight path through free space.
How Does the Free-Space Path Loss (FSPL) & RF Link Budget Calculator Work?
Applies the inverse square law and effective antenna aperture capture area to compute received power in decibels.
Free-Space Path Loss (FSPL) & RF Link Budget Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
ext{FSPL(dB)} = 20 log_{10}(d) + 20 log_{10}(f) + 32.44, quad P_{ ext{rx}} = P_{ ext{tx}} + G_{ ext{tx}} + G_{ ext{rx}} - ext{FSPL} - L
Friis free-space transmission formula with isotropic gain referencing.
How to Use the Free-Space Path Loss (FSPL) & RF Link Budget Calculator
- Enter frequency, link distance, transmitter power, antenna gains, and system losses.
Step-by-Step Example Calculation
10 km Point-to-Point 2.4 GHz Link
Input Values:
frequencyMhz:2400
distanceKm:10
transmitPowerDbm:20
txAntennaGainDbi:14
rxAntennaGainDbi:14
miscellaneousLossesDb:2
Worked Steps: FSPL = 120.0 dB, EIRP = 34.0 dBm, yielding received power P_rx = -74.0 dBm (4.0e-11 W).
Understanding Your Result
Shows path loss in dB and total received signal strength (RSSI), which must exceed receiver sensitivity.
Factors That Affect the Result
- Atmospheric rain fade, fog, and foliage absorption introduce additional losses at frequencies above 10 GHz.
When Should You Use This Calculator?
- Satellite ground station link sizing, outdoor Wi-Fi backhaul design, and LoRaWAN long-range link planning.
Assumptions & Limitations
- Assumes ideal line-of-sight propagation in free space with clear first Fresnel zone.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard Friis transmission equation.