The CNG-70/140 is a fully automated test instrument that sets and maintains a highly accurate ratio between a user-supplied carrier and internally generated White Guassian noise. The instrument operates over a wide range of power levels. The modular design provides one or two totally independent channels covering 50 to 180 MHz. The instrument utilizes the dBm proprietary microprocessor controlled attenuator with 0.015 dB resolution, so resolution uncertainty is less than 0.008 dB. Typical attenuator error is less than 0.02 dB over its entire frequency range and attenuation range. The CNG corrects for noise density and signal level variations over frequency, and integrates the actual noise power over the user defined signal bandwidth. The carrier signal path is never interrupted.