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RF chain

Satellite Link Budget Calculator

Combine uplink, downlink and digital performance requirements.

Given / choose the units

Diagrams update as you edit. Run Calculate to refresh numerical results.

Enter the design inputs, then calculate to inspect the results.

Swipe the diagram sideways to see the full view. With a keyboard, focus the diagram and use the arrow keys.

Uplink C/N₀

Uplink C/N₀EIRP: 60.00 dB; cumulative 60.00EIRP60.0G/T: 5.00 dB; cumulative 65.00G/T65.0Path loss: -205.00 dB; cumulative -140.00Path loss-140.0−10 log k: 228.60 dB; cumulative 88.60−10 log k88.6
Final 88.599 dB-Hz. Each bar begins at the previous cumulative value; gain raises it and loss lowers it. Intermediate terms form a C/N₀ equation, not standalone powers.

Downlink C/N₀

Downlink C/N₀EIRP: 50.00 dB; cumulative 50.00EIRP50.0G/T: 19.23 dB; cumulative 69.23G/T69.2Path loss: -205.00 dB; cumulative -135.77Path loss-135.8−10 log k: 228.60 dB; cumulative 92.83−10 log k92.8
Final 92.829 dB-Hz. Each bar begins at the previous cumulative value; gain raises it and loss lowers it. Intermediate terms form a C/N₀ equation, not standalone powers.

Understand the system

Carrier ledger

At each receive plane, add transmit EIRP and receive gain, then subtract free-space and additional losses. Noise uses the equivalent system temperature at that same plane. Atmospheric absorption reduces carrier and thermal emission can contribute antenna noise; path loss and path noise are different mechanisms.

CdBW=EIRPdBW−Lpath,dB+Gr,dBi−Lother,dBC_{dBW}=EIRP_{dBW}-L_{path,dB}+G_{r,dBi}-L_{other,dB}

C: carrier power; L: positive dB losses.

Every term must belong to the same link direction and reference plane.

Source: week 3/reference.pdf · PDF page 263

Common mistakes

  • Never add C/N values directly in dB.
  • Do not subtract bandwidth twice.
  • Use matching noise reference planes and common bandwidths for composite ratios.
Formula reference and symbol definitions

Carrier to noise

C/N=C/(kTB)C/N=C/(kTB)

C,N: W

Common receive plane and bandwidth.

Example: For carrier 10⁻¹¹ W and integrated noise 10⁻¹³ W, C/N = 100 = 20 dB.

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Carrier to noise density

(C/N0)dBHz=EIRP−L+(G/T)+228.6(C/N_0)_{dBHz}=EIRP-L+(G/T)+228.6

EIRP: dBW; losses: dB; G/T: dB/K

SI Boltzmann reference; matching planes.

Example: With EIRP = 50 dBW, loss = 205 dB and G/T = 20 dB/K, C/N₀ ≈ 50 − 205 + 20 + 228.6 = 93.6 dB-Hz.

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C/N from C/N0

(C/N)dB=(C/N0)dBHz−10log⁡10B(C/N)_{dB}=(C/N_0)_{dBHz}-10\log_{10}B

B: Hz

Noise bandwidth, not symbol rate.

Example: For C/N₀ = 90 dB-Hz and B = 1 MHz, C/N = 90 − 60 = 30 dB.

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Energy per bit

(Eb/N0)dB=(C/N0)dBHz−10log⁡10Rb(E_b/N_0)_{dB}=(C/N_0)_{dBHz}-10\log_{10}R_b

R_b: bit/s

State information/coded bit-rate convention.

Example: For C/N₀ = 90 dB-Hz and Rᵦ = 10 Mbit/s, Eᵦ/N₀ = 90 − 70 = 20 dB.

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Composite C/N approximation

1/Qc=1/Qu+1/Qd1/Q_c=1/Q_u+1/Q_d

Q: linear dimensionless C/N

Independent noises; consistent common bandwidth.

Example: For uplink and downlink ratios of 10 each, Qc = 1/(1/10 + 1/10) = 5 ≈ 6.990 dB.

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Course finite FT ratio

Qc=QuQd/(Qu+Qd+1)Q_c=Q_uQ_d/(Q_u+Q_d+1)

Q: dimensionless linear C/N

Course total-output-power normalization; not C/N₀.

Example: For Qu = Qd = 10, finite FT Qc = 100/(10 + 10 + 1) = 4.762 ≈ 6.778 dB.

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Link margin

M=(Eb/N0)a−(Eb/N0)r−LiM=(E_b/N_0)_a-(E_b/N_0)_r-L_i

All terms: dB

Required BER/modulation/coding threshold and implementation loss.

Example: For available Eᵦ/N₀ = 12 dB, required threshold 9 dB and implementation loss 1 dB, margin = 12 − 9 − 1 = 2 dB.

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Continue the signal path

RF Path, PFD and Received Power Calculator →Noise, Noise Figure and G/T Calculator →Multiple Access, SCPC and TDMA Planner →

Design guide

Technical content reviewed

When this tool is useful

  • Calculating eirp and path loss with engineering models
  • Calculating c/n0 with engineering models
  • Calculating c/n with engineering models

What the result includes

  • Combine uplink, downlink and digital performance requirements.
  • Explanations, assumptions and links to related satellite calculators

What the model does not guarantee

  • Analytical engineering models do not replace measurements or a mission-specific design review.
  • Spectrum permissions, launch operations and real satellite tracking are outside these calculators.

Worked approach

EIRP and path loss

C/N₀ in dB-Hz uses receive G/T and the logarithm of Boltzmann’s constant. Subtract 10 log bandwidth to obtain C/N; subtract 10 log bit rate to obtain Eb/N₀. A symbol rate is not a bit rate unless modulation and coding justify that conversion.

Common decisions

Which topics does Satellite Link Budget Calculator cover?

EIRP and path loss; C/N0; C/N; Eb/N0; FT composite links; Margin; Path noise.

How should I check my work in Satellite Link Budget Calculator?

Read the stated assumptions and source references, check units and independently repeat a worked example before relying on the result.

Does Satellite Link Budget Calculator operate real satellite equipment?

No. This is a browser-based educational resource. It does not transmit RF signals, command spacecraft or certify a working link.

Related build evidence

Related embedded-system engineering

Aqua Sync is a separate connected-device project, not evidence of a satellite deployment.

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