Thermal Noise Calculator
Calculate the noise floor (kTB) of your receiver system based on bandwidth and temperature.
Thermal Noise Quick Facts
Engineering Principles: Johnson–Nyquist Noise (Thermal Noise)
Thermal noise is the electronic noise generated by the thermal agitation of the charge carriers (usually electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.
k=Boltzmann's const, T=Temp(K), B=Bandwidth(Hz)
Standard rule of thumb at room temperature (290K) for 1Hz BW.
RMS voltage across a resistor R due to thermal noise.
Technical Notes
- •Boltzmann's Constant (k) ≈ 1.380649 × 10^-23 J/K.
- •The standard noise floor at room temperature (290K) for 1Hz bandwidth is -174 dBm/Hz.
- •Reducing temperature (cooling) or bandwidth are the primary ways to lower thermal noise.
Frequently Asked Questions
How do I lower thermal noise in my receiver?
According to the formula P = kTB, you can lower noise by reducing Temperature (T) using cryogenic cooling (common in radio astronomy) or by reducing Bandwidth (B) using narrower filters. In most commercial systems, minimizing bandwidth to exactly what is needed for the signal is the most effective strategy.
Does Impedance affect Thermal Noise?
The *Power* of thermal noise (dBm) is independent of impedance—it depends only on temperature and bandwidth. However, the *Voltage* noise (nV/√Hz) IS dependent on impedance (R). A 50Ω resistor generates less noise voltage than a 1MΩ resistor, but into a match load, they deliver the same noise power.
What is the theoretical minimum noise floor?
At room temperature (290 Kelvin), the thermal noise floor is -174 dBm/Hz. This is the absolute physical limit for any uncooled electronic system. A real receiver will have a 'Noise Figure' (e.g., 3dB), raising the actual floor to -171 dBm/Hz.