Link Budget Calculator
RF link analysis for spacecraft communications. Computes EIRP, free-space path loss, received C/N₀, and link margin for a given data rate. Updates as you type.
Inputs
Transmitter
Geometry & band
Receiver
Link budget
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Sign up →Frequently asked questions
What link margin should I design for?
Most space missions target 3 dB of margin for routine operations. Deep-space and critical TT&C links typically require 6 dB or more. The minimum of 0 dB means the link closes — any less and you will drop frames.
How is free-space path loss calculated?
FSPL (dB) = 20·log₁₀(4π·d·f / c), where d is range in meters, f is frequency in Hz, and c is the speed of light. This tool uses d in km and f in GHz and folds the constants: FSPL = 20·log₁₀(d) + 20·log₁₀(f) + 92.45.
What is Eb/N₀ and how does it differ from C/N₀?
C/N₀ is the ratio of carrier power to noise spectral density (dB-Hz). Eb/N₀ subtracts 10·log₁₀(Rb), the bit rate in Hz. So Eb/N₀ = C/N₀ − 10·log₁₀(Rb). The required Eb/N₀ depends on your modulation and FEC coding.
Does this tool include rain fade / atmospheric attenuation?
The "Atmospheric + rain loss" input is where you add it. For X-band and below, 1-2 dB covers most conditions. For Ka-band, 4-8 dB is typical for 99.5% availability. For precise ITU-R rain models, use the full Link Budget tool in the Aerospace Pack.
Need more than this?
- Full modulation & coding library (BPSK through DVB-S2X, LDPC, turbo, convolutional)
- ITU-R P.618 rain attenuation model
- Doppler, pointing loss, and polarization mismatch
- Full pass-schedule C/N₀ vs time with elevation mask
- Save scenarios, compare, export to PDF deliverables
- Traceability to requirements and V&V activities