The NTS contains a noise source which outputs very flat Gaussian noise over a 720 Mhz ± 200 MHz bandwidth range. This noise is attenuated by noise attenuators in 0.1 dB, 1 dB, and 10 dB steps and then added to the attenuated signal to produce calibrated 10 log Eb/No levels. The SNR attenuator allows one to then vary 10 log Eb/No over a 10 dB range in 1 dB steps while the signal plus noise range attenuator allows one to keep a constant SNR while varying signal levels in 1 dB steps over the complete signal range of the demodulator. The signal path from input to output is very flat over the frequency range and the signal attenuators allow one to set the signal level to the desired output power. Several cavity filters centered on 720 MHz plus an associated attenuator and amplifier powered by the NTS are provided for calibration of 10 log Eb/No levels.