User Manual

VoiceXtender Modem Installer’s Guide
System Planning
2-6 Rev. A - 8/97
Typically, the largest contributor to “link loss” is the loss of power as the
signal travels through space. This contribution, called Free Space Path Loss,
can be easily calculated as follows: To determine the free space path loss,
determine the distance between the VX modems for your application and refer
to Table 2-1, or use the following formula:
attenuation in dB = [96. 6 + 20 LOG (distance in miles)
+ 20 LOG (frequency in GHz)]
Table 2-1
Free Space Path Loss Between Two Isotropic Radiators
Distance
(Miles)
Path Loss
@ 915 MHz
(L-Band)
1 96 dB
2 102 dB
3 105 dB
4 108 dB
5 110 dB
6 111 dB
7 113 dB
8 114 dB
9 115 dB
10 116 dB
15 120 dB
20 123 dB
25 125 dB
30 126 dB