Noise Diode
Understanding Noise Diodes
Noise diodes are the calibration standard for noise figure measurement. The Y-factor method, the most common NF measurement technique, requires a calibrated noise source with known ENR at each frequency.
Y-Factor Method
- Connect noise diode to DUT input.
- Measure output noise power with diode OFF (cold noise, N_c).
- Measure output noise power with diode ON (hot noise, N_h).
- Y = N_h / N_c (the Y-factor).
- NF = ENR - 10log(Y - 1) dB.
Noise Source Specifications
- ENR (Excess Noise Ratio): Calibrated noise above thermal. 5-6 dB (low ENR) or 15 dB (standard).
- Frequency range: 10 MHz to 40+ GHz.
- VSWR: < 1.3 for accurate measurement.
- Calibration: ENR calibrated at factory with traceable standards.
Frequently Asked Questions
What is a noise diode?
A noise diode generates calibrated broadband noise for noise figure measurement. When reverse-biased, it produces known ENR (5-15 dB above thermal). Used with the Y-factor method to accurately measure device noise figure.
What is ENR?
ENR (Excess Noise Ratio) is the noise power above thermal (290K) that the noise source generates when turned on. ENR = 10log((T_hot - T_cold)/T_0). A 15 dB ENR means the source produces ~9200K noise temperature.
When should I use low vs high ENR?
Low ENR (5-6 dB): For measuring very low NF devices (< 3 dB), provides more accurate results by avoiding receiver compression. High ENR (15 dB): For measuring higher NF devices or when the measurement system has high loss before the DUT.