Noise Figure Calculator
An interactive tool to calculate the cascaded noise figure and gain of an RF system.
System Calculator
Enter the gain and noise figure for each stage in your receiver chain. The total system values will update automatically.
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Total Noise Figure (dB)
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Total Gain (dB)
Core Concepts
This tool helps you understand how individual component performance affects the overall sensitivity of a system, like a radio receiver. The two key parameters are Noise Figure and Gain.
Noise Figure (NF): A measure of the degradation in the signal-to-noise ratio (SNR) caused by a component. It's expressed in decibels (dB). A lower noise figure is better, as it means the component adds less unwanted noise to the signal.
Gain: A measure of a component's ability to increase the power of a signal, also expressed in dB. High gain amplifies both the signal and the noise present at the component's input.
In a chain of components (a cascade), the noise figure of the very first component has the most significant impact on the total system noise figure. This is why a Low Noise Amplifier (LNA) is the critical first block in sensitive receivers.
The Friis Formula
The calculator uses the Friis formula to determine the total noise figure of a cascaded system. The formula shows that the noise from each subsequent stage is divided by the total gain of all preceding stages, diminishing its impact.
Ftotal = F1 + (F2 - 1)/G1 + (F3 - 1)/(G1G2) + ...
Note: The formula uses Noise Factor (F) and Gain (G) in linear terms, not dB. The calculator handles all conversions for you.
Noise Contribution by Stage
This chart visualizes each stage's contribution to the total system noise factor. Notice how the first stage's contribution is typically the largest. Change the values in the calculator above to see how the chart reacts instantly.
Frequently Asked Questions
Noise Factor (F) is a linear ratio of the input SNR to the output SNR. Noise Figure (NF) is simply the Noise Factor expressed in decibels: NF (dB) = 10 * log10(F).
As the Friis formula shows, the noise contribution of any stage is reduced by the total gain of the stages before it. Since the first stage has no preceding gain to reduce its noise contribution, its own noise figure is added directly to the system's total. Therefore, using a component with a low noise figure and reasonable gain in the first stage is crucial for sensitive system design.
Yes. Noise Figure is defined relative to a standard temperature, typically 290 K (about 17°C or 62°F). The actual noise power generated by a component is dependent on its physical temperature. For most standard calculations, the reference temperature is assumed, but in high-precision applications like radio astronomy or satellite communication, Noise Temperature is often used instead of Noise Figure for more accuracy.