ENR
Understanding ENR
ENR is the key specification of a noise source used for noise figure measurement. A noise source with higher ENR produces more noise power, which is useful for measuring devices with high noise figures. Lower ENR noise sources are more accurate for measuring very low noise figures.
Y-Factor Method
The Y-factor method measures noise figure by comparing the output noise of the DUT with the noise source ON (hot) vs OFF (cold). Y = P_hot/P_cold. Then: NF = ENR - 10 log10(Y - 1).
ENR Selection
- Standard ENR (~15 dB): General purpose, suitable for devices with NF > 3 dB.
- Low ENR (~5-6 dB): More accurate for measuring NF < 3 dB. Less measurement uncertainty.
- High ENR (~25 dB): Used for measuring high-NF devices (mixers, receivers).
where T0 = 290K, Tc = 290K (typically)
ENR = 15 dB: Th = 9,454K
ENR = 6 dB: Th = 1,445K
Y-factor noise figure measurement:
Y = P_hot / P_cold
NF = ENR (dB) - 10 log10(Y - 1)
Frequently Asked Questions
What is ENR?
ENR (Excess Noise Ratio) specifies the noise output of a calibrated noise source used for noise figure measurement. It is the ratio (in dB) of the noise source's excess noise to the thermal noise at 290K. Standard values are 5, 6, and 15 dB.
How is ENR used to measure noise figure?
Using the Y-factor method: measure the DUT output noise with noise source ON (hot) and OFF (cold). Calculate Y = P_hot/P_cold. Then NF = ENR - 10 log10(Y - 1). The noise source ENR must be known accurately for precise measurements.
Should I use high or low ENR?
Use low ENR (5-6 dB) for measuring low noise figures (< 3 dB), as it provides lower measurement uncertainty. Use standard ENR (15 dB) for general measurements. Use high ENR (25 dB) for high-NF devices like mixers where the Y-factor would be too close to 1 with low ENR.