Handbook of Propagation Effects for Vehicular and ... - Courses

8-10
Relative Signal Level (dB)
4
2
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
-32
-34
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
Frequency
725.3 MHz
729.7 MHz
735.2 MHz
739.6 MHz
745.1 MHz
749.5 MHz
0 10 20 30 40 50 60 70 80 90 100
Distance (cm)
Figure 8-5: Relative signal level versus vertical measurement distance at six frequencies
spaced approximately 5 MHz apart. (Site 2).
8.2.7 Bandwidth Distortion Considerations
At relative signal levels down to approximately -15 dB, the multipath delays tended to be
less than 100 ns consistent with the results in Figure 8-2. We may imply from this result
that contemplated systems with bandwidths of up to about 1 MHz should not be
adversely affected by signal distortion. Vogel and Torrence executed an investigation to
establish the expected levels of signal distortion one might encounter by examining the
losses at various bandwidths ranging from 2 MHz to 90 MHz. The signal distortion was
described in terms of the standard deviation of the deviations relative to the mean signal
loss at each bandwidth. Since the standard deviation was found to be frequency
insensitive, the results were combined over each frequency interval considered (e.g., 700
to 800 MHz, 800 to 900 MHz, … 1700 to 1800 MHz), and are shown plotted in Figure
8-6 for the “average” and “best” cases for Site 4. It is noted that at a 2 MHz bandwidth
the standard deviation is approximately 0.5 dB, whereas the deviations become
considerably larger at 90 MHz, ranging from 2.5 to 3.5 dB.