Satellite Link Budget Calculator
Calculate total link loss, incident power, C/N₀, Carrier-to-Noise Ratio (C/N), and Eb/N₀ for satellite communication links.
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Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
C/N₀ = EIRP - FSPL - L_misc + G/T + 228.6 (dB-Hz), C/N = C/N₀ - 10 log₁₀(B_Hz)This formula is used to calculate antenna parameters for satellite link budget calculator.
Overview
This satellite link budget calculator evaluates the complete power chain of a satellite RF link — EIRP, path loss, receive G/T, and channel bandwidth — to produce carrier-to-noise density (C/N₀) and carrier-to-noise ratio (C/N) across L, C, Ku, and Ka bands. It is built for RF link engineers, satellite systems designers, and students verifying whether a proposed uplink or downlink will close with adequate margin before committing to hardware.
Input Guide
Enter Transmit EIRP, Path Loss (FSPL), Receive G/T, Atmospheric & Misc Losses, Channel Bandwidth exactly in the units shown by this satellite link budget. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Transmit EIRP — use dBW.
- Path Loss (FSPL) — use dB.
- Receive G/T — use dB/K.
- Atmospheric & Misc Losses — use dB.
- Channel Bandwidth — use MHz.
Output Guide
The results describe the calculated satellite link budget values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Satellite Link Budget uses C/N₀ = EIRP - FSPL - L_misc + G/T + 228.6 (dB-Hz), C/N = C/N₀ - 10 log₁₀(B_Hz). Supply Transmit EIRP (dBW), Path Loss (FSPL) (dB), Receive G/T (dB/K), Atmospheric & Misc Losses (dB), Channel Bandwidth (MHz) in the displayed units, then use the calculated values as the first engineering target for this satellite communication design or analysis.
Design Notes
A link budget is fundamentally a running tally of every gain and every loss a signal encounters from transmitter to receiver, expressed in decibels so the entire chain can be summed with simple addition and subtraction rather than multiplying raw power ratios. The +228.6 dBW/(Hz·K) constant is the logarithmic form of Boltzmann's constant and converts system noise temperature directly into a noise power density floor, which is why receive G/T — combining antenna gain and system noise temperature into one figure — sits at the center of the C/N₀ equation. Unlike a pure downlink power calculation, this budget folds in channel bandwidth explicitly, letting you see how C/N (not just raw C/N₀) responds to bandwidth choices for different modulation schemes.
Build and Tuning Notes
To confirm a link will actually close, compare the calculated C/N or the derived Eb/N₀ against your specific modem's required threshold for its modulation scheme — QPSK typically needs less Eb/N₀ than 8PSK or 16APSK, which trade higher spectral efficiency for a higher required signal quality. Always build in an operational fade margin, commonly 3–6 dB, to absorb rain fade, pointing error, and equipment aging beyond the nominal calculated values; a link that barely closes on paper with zero margin is not a reliable design. Narrower channel bandwidth improves C/N for a fixed C/N₀ since noise power scales with bandwidth, which is why bandwidth-efficient modulation and coding choices are often as important as raw power in closing a marginal link.
Frequently Asked Questions
What is the difference between C/N₀ and C/N?
C/N₀, or carrier-to-noise density ratio, measures carrier power relative to noise power normalized to a 1 Hz bandwidth, expressed in dB-Hz, making it independent of the actual channel width. C/N, or carrier-to-noise ratio, measures carrier power relative to the total noise power across your full modulated channel bandwidth, expressed in dB, and is what ultimately determines whether your specific demodulator can lock onto the signal.
How do you convert C/N₀ to Eb/N₀?
Subtract ten times the base-10 logarithm of your data rate in bits per second from C/N₀. This conversion, energy per bit relative to noise spectral density, allows fair comparison of link quality across different modulation and coding schemes independent of the specific bandwidth or symbol rate used.
Where does the +228.6 constant come from in link budget equations?
It is the logarithmic representation of Boltzmann's constant, calculated as negative ten times the base-10 logarithm of 1.380649 × 10⁻²³ joules per Kelvin, which works out to approximately +228.6 dBW per Hz per Kelvin. This constant converts system noise temperature into an equivalent noise power density, forming the noise floor against which carrier power is compared.
Why does channel bandwidth affect C/N even when C/N₀ stays fixed?
C/N₀ describes noise density in a 1 Hz reference bandwidth, but your actual receiver integrates noise across its full channel bandwidth, so wider channels collect proportionally more total noise power. This is why narrowing bandwidth (at the cost of lower data throughput) improves C/N for a fixed C/N₀, and why bandwidth choice is a direct engineering tradeoff against link margin.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.