🛰️ Satellite Link Budget Calculator

LEO / Smallsat & ground-station link analysis — EIRP, FSPL, G/T, C/N₀, Eb/N₀ & margin

Saved Scenarios已保存场景

Save the current inputs as a named scenario, then compare two or more side by side (same-mode scenarios only).

把当前输入保存为命名场景，再对比两个或更多场景(仅同模式之间可对比)。

Single Link单链路
TT&C测控
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Transmitter

Propagation Path

Receiver

Interference (optional)

Data Link / Modem

Results

EIRP
– dBW
Free space path loss
– dB
Total path loss
– dB
G/T
– dB/K
C/N₀
– dB-Hz
Eb/N₀ (received)
– dB
Spectral efficiency
– bit/s/Hz
Occupied bandwidth
– MHz
C/N (received)
– dB
C/(N+I)
– dB
C/N (required)
– dB
–
Show full calculation breakdown

Reverse Solver

Given a target link margin, solves the limiting value of one variable. All other inputs stay as set above.

给定目标链路余量，反推单个变量的极限值，其余输入保持上面的设定。

Link Margin vs Elevation Angle

Sweeps from horizon (0°) to zenith (90°). Slant range is derived from altitude.

扫描从地平线(0°)到天顶(90°),斜距由轨道高度推得。

Pass Data Budget

Estimates contact time per pass based on orbit altitude and minimum working elevation, then computes data volume per pass at the current data rate.

根据轨道高度和最低工作仰角估算每次过境接触时长，按当前数据率计算每次过境数据量。

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📖 How to use

  1. Pick a preset or use Single Link / TT&C tabs for different analysis modes.选一个预设,或用上方标签切换单链路 / 测控分析模式。
  2. Fill in Transmitter, Path, Receiver and Modem — power, gains, frequency, slant range, data rate.填写发射机、路径、接收机和调制解调器参数——功率、增益、频率、斜距、数据率。
  3. Don't know a value? Click the small ↗ link next to Tx power, antenna gains, noise temperature or rain/atmospheric loss — it opens the matching tool, and its return bar brings the computed value straight back into this field.某个参数不会填?点字段旁的 ↗ 小链接(发射功率、天线增益、噪温、雨衰/大气损耗等)——跳到对应工具计算,再点其顶部返回条即可把结果直接带回本字段。
  4. Optionally add Interference C/I entries (adjacent satellite, cross-pol, HPA intermod — use ↗ HPA Backoff to estimate C/I₃); the margin is then computed on C/(N+I).可选填写干扰各项 C/I（邻星、交叉极化、HPA 互调——可用 ↗ HPA 回退估算 C/I₃），余量将按 C/(N+I) 计算。
  5. For a downlink, turn on Rain sky-noise coupling — rain/gas absorption also raises the receive noise temperature (ΔT = T_m·(1−10^(−A/10))), often costing as much margin as the fade itself.下行链路建议开启雨致天空噪声耦合——雨/大气吸收同时抬升接收噪温（ΔT = T_m·(1−10^(−A/10))），其代价常与雨衰本身相当。
  6. Choose a Modulation / coding scheme; required Eb/N₀ fills automatically.选择调制/编码方式,所需 Eb/N₀ 自动填入。
  7. Read the Link margin: green ≥ 3 dB, amber 0–3 dB, red = link fails.看链路余量:绿 ≥ 3 dB、黄 0–3 dB、红 = 链路不通。
  8. Set the orbit altitude to sweep the Margin vs Elevation chart over a whole pass — it marks the lowest elevation where the link closes (≥ 0 dB) and where it is comfortable (≥ 3 dB).设置轨道高度,余量-仰角曲线会扫描整个过境,并标出链路闭合(≥ 0 dB)和余量充足(≥ 3 dB)的最低仰角。
  9. Ask the question backwards with the Reverse Solver: given a target margin, it solves the max data rate, min Tx power, min antenna gain or max slant range — Apply writes the value into the form.用反算求解反过来提问:给定目标余量,反解最大数据率、最小发射功率、最小天线增益或最大斜距——点填入即可写回表单。
  10. Check Pass Data Budget for contact time and data-per-pass at your data rate.查看过境数据预算——当前数据率下每次过境的接触时长与数据量。
  11. Click 📑 Scenarios to save the current setup, reload it later, or select several saved scenarios and compare them side by side.点📑 场景保存当前设置,之后可重新载入,或勾选多个已存场景进行并排对比。
  12. Click ↓ Export PDF to save a formatted calculation report.点击 ↓ 导出 PDF 保存格式化计算报告。

What is a satellite link budget?

A link budget accounts for all gains and losses from transmitter to receiver. It tells you whether a satellite link will close — whether the received signal is strong enough to be demodulated at your target BER — and how much margin you have against fades.

The equations used by this calculator

EIRP = Ptx(dBW) + Gtx(dBi) − Ltx(dB)

FSPL = 32.44 + 20·log₁₀(dkm) + 20·log₁₀(fMHz) dB

G/T = Grx(dBi) − 10·log₁₀(Tsys) dB/K   — both terms at the antenna aperture, so Tsys must already include the feed loss's (L−1)·Tphys noise, as the G/T tool reports it. The Rx line loss is not subtracted a second time.

C/N₀ = EIRP − Lpath + G/T − k   (k = −228.6 dBW/K/Hz)

Eb/N₀ = C/N₀ − 10·log₁₀(Rb)

ΔTsky = Tm·(1 − 10−Aabs/10) — rain/gas absorption raises the receive noise temperature (downlink); G/T uses Tsys+ΔT

C/(N+I) = −10·log₁₀(10−(C/N)/10 + 10−(C/I)/10) — aggregate C/I combines adjacent-satellite, cross-pol and intermod entries as powers

Link margin = Eb/N₀rx − interference degradation − Eb/N₀req − implementation loss

Typical LEO smallsat values

CubeSat S-band downlink: ~2 W TX, 6 dBi patch, 3 m ground dish (~30 dBi), 1500–2500 km slant range, 150–250 K noise temp. Keep at least 3 dB margin at the minimum operating elevation.

什么是卫星链路预算?

链路预算把无线信号从发射机到接收机所经历的全部增益与损耗逐项累加。它告诉你链路能否"闭合"，以及针对衰落留有多少余量。

本计算器使用的公式

EIRP = Ptx(dBW) + Gtx(dBi) − Ltx(dB)

FSPL = 32.44 + 20·log₁₀(dkm) + 20·log₁₀(fMHz) dB

G/T = Grx(dBi) − 10·log₁₀(Tsys) dB/K   —— 两项都参考天线口面，因此 Tsys 必须已包含馈线损耗贡献的 (L−1)·Tphys 噪声，即 G/T 工具给出的那个值。接收线损不再二次扣除。

C/N₀ = EIRP − Lpath + G/T − k   (k = −228.6 dBW/K/Hz)

Eb/N₀ = C/N₀ − 10·log₁₀(Rb)

ΔTsky = Tm·(1 − 10−Aabs/10) —— 雨/大气吸收同时抬升接收噪温(下行)，G/T 按 Tsys+ΔT 计算

C/(N+I) = −10·log₁₀(10−(C/N)/10 + 10−(C/I)/10) —— 合计 C/I 由邻星、交叉极化与互调各项按功率合成

链路余量 = Eb/N₀接收 − 干扰恶化量 − Eb/N₀所需 − 实现损耗

典型 LEO 小卫星取值

立方星 S 波段下行：~2 W、6 dBi 贴片、3 m 地面站碟(~30 dBi)、斜距 1500–2500 km、噪温 150–250 K。最低工作仰角处至少保留 3 dB 余量。