Satellite Link Budget Calculator

Inputs

Frequency

GHz

Examples: 6, 12, 14, 20, 30.

Slant range

GEO is commonly near 38,000 km.

Transmit power

If you enter watts, it converts to dBW.

TX antenna gain

dBi

TX feeder / line loss

TX pointing loss

Polarization mismatch loss

Atmospheric absorption loss

Rain / fade allowance

Increase for higher availability in wet climates.

Misc. losses

Covers radome, depointing, aging, etc.

Receiver mode

Use direct G/T when you have a spec.

RX antenna gain

dBi

RX feeder / line loss

System noise temperature

Includes antenna + LNB/LNA contribution.

Bandwidth

MHz

Data rate

Mbps

Used for Eb/N0 and spectral efficiency.

Implementation loss

Accounts for modem and non-idealities.

Required Eb/N0

Use your modulation/coding requirement.

Target availability

Presentation options

Show an uplink loss split

Show a downlink loss split

Splits are for display only unless you edit losses.

Reset

Scenario	Frequency (GHz)	Range (km)	EIRP (dBW)	G/T (dB/K)	Eb/N0 eff. (dB)	Margin (dB)
Ku-band GEO, moderate fade	14.0	38,000	53.500	19.990	7.282	0.782
Ka-band GEO, higher rain loss	30.0	39,500	56.000	18.500	6.100	-0.900
C-band GEO, low fade	6.0	37,500	50.200	20.800	9.500	3.000

Formula used

EIRP (dBW) = P_TX(dBW) + G_TX(dBi) − L_TX(dB)
FSPL (dB) = 92.45 + 20log₁₀(f_GHz) + 20log₁₀(R_km)
G/T (dB/K) = (G_RX − L_RX) − 10log₁₀(T_sys,K)
C/N0 (dB‑Hz) = EIRP − L_total + G/T − 228.6
C/N (dB) = C/N0 − 10log₁₀(B_Hz)
E_b/N0 (dB) = C/N0 − 10log₁₀(R_b)
Link margin (dB) = (E_b/N0 − L_impl) − (E_b/N0)_req

L_total includes FSPL plus polarization, atmospheric, rain, and miscellaneous losses. Receiver feeder loss is included inside G/T when derived.

FAQs

1) What does link margin mean here?

Link margin is the difference between effective Eb/N0 and your required Eb/N0. Positive margin suggests headroom against fades and implementation losses.

2) Should I enter G/T directly or derive it?

Use direct G/T when you have a terminal specification. Derive it when you know receive gain, feeder loss, and system noise temperature.

3) Why is rain loss important for availability?

Rain attenuation can dominate at higher frequencies and drives fade margin for high availability targets. Local rainfall statistics strongly influence required fade allowance.

4) What bandwidth should I use, occupied or assigned?

Use the noise bandwidth that matches your receiver filter or channel allocation. For practical planning, the assigned channel bandwidth is a reasonable starting point.

5) How do I choose required Eb/N0?

Use modem performance curves for your modulation and coding, including required BER or PER. Add extra margin if you expect interference or imperfect tracking.

6) What if my data rate exceeds my bandwidth?

That implies very high spectral efficiency and usually needs higher order modulation and strong coding. Verify roll-off, coding rate, and whether the bandwidth value is correct.

7) Does this include satellite transponder saturation effects?

No. This focuses on thermal noise budgeting. If you operate near saturation, consider output backoff, intermodulation, and adjacent channel limits separately.

8) Can I use this for LEO links?

Yes, but update slant range and add Doppler and tracking losses if needed. LEO geometry changes rapidly, so compute range and pointing over the pass.