ison had a DS-3 capacity, which is the same as 28 T-1 capacity. The digital system thus has 2.8 times the T-1 capacity of the analogue system. This comparison of capacity is also given in Table 50.3. For this case (similar bandwidth and voice channel capacity), the Analogue FM NPR per hop (dB) digital microwave system appears to be vastly superior in data or T-1 capacity over the analogue FM system. In the preceding examples, the bandwidth and the voice channel Figure 50.28 An estimate of system size above which capacity of the analogue FM and digital microwave systems were TDM/DS-3 digital multiplex/microwave offers potential voice similar. It might also be reasonable to compare analogue FM and channel performance advantages over analogue FDM/600 digital microwave microwave systems of similar data rate or T-1 channel FM multiplex/microwave capacity. An analogue FM system with a maximum data rate capac- ity of 11.52mbit/s or a T-1 capacity of 10 DS-1s, can be compared to a digital microwave system having a capacity of about 12.75Mbit/s and a T-1 capacity of 8 DS-1. (See Table 50.4. The In general, it may be said that there is some system size limit, same conditions as Table 50.3 apply.) above which a digital microwave/multiplex system begins to offer significant performance advantages, even for the voice channel In this case the bandwidths are not comparable, the digital micro- wave system is much more efficient since it requires only 5 or users. 3.5MHz of microwave bandwidth vs. the analogue FM requirement of 10MHz. However, the digital system has PCM voice channel 50.3.5 Channel capacity comparisons Table 50.4 Comparison of approximately the same data In the previous examples, DS-3 digital microwave of 10MHz band- capacity analogue and digital microwave width was compared with 600 channel FM analogue microwave because the voice channel capacities are similar. However, the data capacities of these types are not similar. 600 channel FM 16 QAM/49 QPRS For example, the data channel modems assumed for the analogue a