📐 G/T Figure-of-Merit Calculator

Build system noise temperature from antenna, feed, LNA & receiver → G/T in dB/K

Ad placeholder

Antenna

Feed / Line before LNA

LNA & Receiver

Results

LNA noise temp
– K
Effective Rx noise temp
– K
System noise temp T_sys
– K
T_sys
– dBK
G/T figure of merit
– dB/K
Show noise temperature breakdown
Ad placeholder

📖 How to use

  1. Enter the antenna gain (from the Antenna tool) and the antenna noise temperature (sky + ground pickup).输入天线增益(可由天线工具得到)和天线噪声温度(天空 + 地面拾取)。
  2. Add the feed loss before the LNA and its physical temperature (≈290 K).填入 LNA 之前的馈线损耗及其物理温度(≈290 K)。
  3. Enter the LNA noise figure & gain, and the post-LNA receiver noise figure.输入 LNA 噪声系数与增益,以及 LNA 之后接收机的噪声系数。
  4. Read G/T (dB/K) — paste it straight into the link budget's G/T input.读取 G/T(dB/K)——直接填进链路预算的 G/T 输入。
  5. Open the breakdown to see how each stage adds to the system noise temperature (pre-LNA loss hurts most).展开明细可看各级对系统噪温的贡献(LNA 前的损耗影响最大)。
  6. Arrived via the ↗ link next to the Link Budget's system-noise-temperature field? The return bar at the top carries T_sys (K) back — the link budget derives G/T itself (no bar appears on a direct visit).如果是点链路预算系统噪温字段旁的 ↗ 链接跳转而来,顶部返回条带回的是 T_sys(K)——G/T 由链路预算自行推算(直接访问不会显示返回条)。

What is G/T?

G/T (gain-to-noise-temperature ratio, the "figure of merit") summarises a receiving system's sensitivity in a single number: the antenna gain divided by the total system noise temperature, expressed in dB/K. Higher is better. It feeds directly into the carrier-to-noise calculation: C/N₀ = EIRP − path loss + G/T − k.

Formulas used

Noise temperature from noise figure: T = (10^(NF/10) − 1) · 290 K

System noise temp referred to the antenna aperture (Friis cascade):

T_sys = T_A + (L−1)·T_phys + L·T_LNA + L·T_rx / G_LNA

where L is the linear feed loss before the LNA. Because the loss sits ahead of the LNA, it both adds its own noise and attenuates the signal — which is why keeping pre-LNA loss tiny matters so much. Finally: G/T = G_antenna(dBi) − 10·log₁₀(T_sys).

Plug the resulting G/T straight into the link budget calculator. All computation runs locally in your browser.

什么是 G/T?

G/T(增益与噪声温度之比,即"品质因数")用一个数概括接收系统的灵敏度:天线增益除以系统总噪声温度,单位 dB/K。越高越好。它直接进入载噪比计算:C/N₀ = EIRP − 路径损耗 + G/T − k。

使用的公式

由噪声系数得噪声温度:T = (10^(NF/10) − 1) · 290 K

折算到天线口面的系统噪温(Friis 级联):

T_sys = T_A + (L−1)·T_phys + L·T_LNA + L·T_rx / G_LNA

其中 L 为 LNA 之前的线性馈线损耗。由于该损耗位于 LNA 之前,它既引入自身噪声又衰减信号——这正是把 LNA 前损耗做到极小如此重要的原因。最后:G/T = G_antenna(dBi) − 10·log₁₀(T_sys)。

把得到的 G/T 直接填进链路预算计算器。全部计算在你的浏览器本地完成。