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Satellite Link Signal Budget Planner

The Satellite Link Signal Budget Planner estimates received power and link margin for a satellite communication path. It uses transmitter power, carrier frequency, slant range, antenna gains, aggregate losses, and receiver sensitivity to form a conventional free-space link budget.

Use it to test first-order downlink or uplink scenarios before building a more complete Eb/N0 or C/N0 analysis. The calculator is especially helpful for comparing ranges, antenna gains, or transmitter power because each change is reflected directly in dB margin. A positive margin means the received-power estimate exceeds the threshold entered; it does not guarantee service availability because fading, interference, atmospheric effects, polarization, pointing, modulation, coding, and noise conditions may require additional analysis.

Inputs

W
MHz
km
dBi
dBi
dB
dBm
Result
—
Satellite link margin
Received power—
Free-space path loss—
Transmit power—

1. Enter RF power
Use transmitter output power in watts.

2. Enter frequency and slant range
Use MHz and kilometers for the specific pass geometry being evaluated.

3. Enter antenna gains
Use the gains toward the link partner, in dBi.

4. Combine additional losses
Include cable, pointing, polarization, atmospheric, radome, or implementation losses as appropriate.

5. Enter receiver sensitivity
Use the threshold that corresponds to your receiver and waveform assumption.

6. Review margin
Positive dB means the modeled received power is above the threshold.

Pₜ(dBm) = 10 log₁₀(Pₜ(W) × 1000) FSPL(dB) = 32.44 + 20 log₁₀(fMHz) + 20 log₁₀(Rkm) Pᵣ(dBm) = Pₜ + Gₜ + Gᵣ − FSPL − Losses Margin(dB) = Pᵣ − Sensitivity

The constant 32.44 is used when frequency is in MHz and distance is in kilometers.

What the result means

The main result is received-power margin relative to the receiver sensitivity entered.

A complete digital link budget commonly uses noise temperature, bandwidth, C/N0, Eb/N0, coding and implementation losses rather than receiver sensitivity alone.

Given: 20 W, 8,400 MHz, 1,500 km, 8 dBi transmit gain, 35 dBi receive gain, 3 dB additional losses, and −120 dBm sensitivity.

Calculation: Pₜ ≈ 43.01 dBm. FSPL ≈ 174.46 dB. Pᵣ ≈ 43.01 + 8 + 35 − 174.46 − 3 = −91.45 dBm. Margin ≈ 28.55 dB.

Result: The simplified link has about 28.6 dB of margin.

Should I use orbital altitude as range?

Not necessarily. Use slant range between the two antennas; it can be much larger than altitude near the horizon.

What belongs in other link losses?

Typical entries can include feeder, polarization, pointing, atmospheric, radome, and implementation losses when they are not already embedded in antenna gain or sensitivity.

Can this calculate both uplink and downlink?

Yes, if you enter the appropriate transmitter, receiver, antennas, frequency, range, and losses for the direction being evaluated.

Why might margin change during a pass?

Slant range, antenna pointing, atmospheric path length, and sometimes hardware state change as the satellite moves.

Is receiver sensitivity enough for a final design?

Usually not. Detailed digital-link design should connect received carrier power to noise, bandwidth, modulation, coding, and required quality of service.