tortion In the NPR test, the multiple channel baseband signal is repre- sented by a noise generator adjusted for the equivalent power level and frequency spectrum (see Figure 50.30). At the system output the NPR (dB) Test tone level in mux channel Figure 50.31 The bucket curve Noise to simulate all other channels in use NPR (dB) If the received microwave signal level could be increased above Noise plus distortion level 'normal' level perhaps due to increased transmitter power, the (all channels in use) receiver thermal noise contribution could be decreased. Equival- ently, improved receiver sensitivity, given a fixed received level, would also decrease the receiver thermal noise contribution and result in improved NPR. This improvement could be achieved if NPR is not already significantly limited by idle and intermodulation Baseband frequency distortion noise. Thus, it can be seen that System Gain may some- what control NPR. Figure 50.30 NPR test It should not be forgotten that in the actual system, there are yet more noise contributors, namely co-channel and adjacent channel interference, and echo distortion. These will not be discussed here, power of this noise is measured in the channel under test. The noise but are mentioned as a reminder that system NPR is partly in the generator spectrum is then notched at the frequency of the channel hands of the system designer. under test. At the system output, the residual noise power is It is interesting to note also that if idle and intermodulation could measured in the channel under test. The ratio of these two readings be entirely eliminated by clever design, and given that baseband is the Noise Power Ratio. An ideal, noiseless, distortionless system levels are fixed at their current levels by bandwidth considerations, would have an infinite NPR. and given that received levels remain essentially at the current Due to the nature of NPR, all sources of channel degradation are levels due to receiver overload considerations, the typical NPR included. The microwave radio