.00 Analogue (Topslot) (hops) voice/noise 25.00 66.11 64.62 49.62 60.38 59.93 44.93 20.00 57.72 57.47 42.47 15.00 55.97 55.80 40.80 54.66 54.53 39.53 Received level (dBm) 53.61 53.51 38.51 52.74 52.66 37.66 Figure 50.25 Voice-To-Noise performance with one hop fading in a hypothetical 13 hop system. Digital is a PCM 51.99 51.93 36.93 channel on DS-3 microwave. Analogue is 2438kHz voice 51.34 51.28 36.28 channel of 600 channel FM microwave 50.76 50.71 35.71 50.24 50.19 35.19 49.77 49.73 34.73 1E -12 Analogue microwave 49.33 49.29 34.29 1E -10 Low-mid slot 534 KHz 48.93 48.90 33.90 1E -8 Mid slot 1248 KHz 48.56 48.53 33.53 1E -6 Top slot 48.21 48.18 33.18 2438 KHz 1E -4 47.88 47.86 32.86 1E -2 47.58 47.55 32.55 Data on digital microwave 47.29 47.27 32.27 47.01 46.99 31.99 Received level (dBm) 46.75 46.73 31.73 Figure 50.26 Low speed data channel performance on Table 50.2 Parameters for Table 50.1 analogue vs. digital microwave. One hop fading in 13 hop system. Digital microwave = DS-3, 10MHz BW. Data channel on analogue = 32 QAM, 12kBit/s. Analogue microwave = 600 channel, FM, 10MHz BW Parameter Value No. of Channels 600.00 12.78dB 28.89dB a data modem on the analogue system improves further if lower frequency baseband slots are used (see Figure 50.26). S/N - NPR 16.11dB For high speed data, however, the situation is different. The 18.00dBrncO performance of a 256 QAM T-1 baseband modem is almost always NPR1hop 50.00dB worse than the performance of a T-1 on digital microwave, unless it is located in the low frequency end of the analogue baseband, in S/N1hop 66.11dB which case it may have equivalent performance (see Figure 50.27). The 13 hop figure used in the above comparison must be accepted only as a typical system size, above which, the digital micro- approach seems to be equal to or superior to the analogue for voice wave/multiplex system provides performance advantages, and channel usage. below which the analogue microwave/multiplex provides perfor- For a voice channel data modem, and using the same 13 hop manc