User's Manual

FT-512 Trailblazer Installation and User Manual version 1.09 9
antennas so that the first Fresnel zone signal path is clear and the second is
obstructed.
2.3.3 Radio Path Losses
After confirming not only line of sight and adequate Fresnel zone clearance, it is
then time to look at the Free Space Loss of the radio signal, RF cable losses,
and antenna gains to determine how much is left over. The remaining signal is
called the “Fade Margin”.
Distance Distance Ant Gain Ext RF Path Loss RF power ERP Link Margin
in miles in km in dBi Cable(s) in dB in dBm in dBm in dB
1.5 2.4 14.0 0.0 108 17 31 28.0
2.0 3.2 14.0 0.0 110 17 31 25.5
5.0 8.0 14.0 0.0 118 17 31 17.6
8.0 12.9 14.0 0.0 122 17 31 13.5
10.0 16.1 14.0 0.0 124 17 31 11.5
12.0 19.3 14.0 0.0 126 17 31 10.0
14.0 22.5 14.0 0.0 127 17 31 8.6
20.0 32.2 24.0 1.4 130 17 41 24.1
35.0 56.3 24.0 1.4 135 17 41 19.3
50.0 80.5 24.0 1.4 138 17 41 16.2
Table 2: Fade Margin Chart
The above chart shows various antenna and distance combinations. A
changeable Excel spreadsheet is available on the world wide web at
www.carlsonwireless.com/support.html The 24 dB gain external antenna option
is only available through factory trained dealers.
What’s an acceptable “Link Margin“? A rule of thumb theory is that 10 dB of fade
margin will deliver about 90% reliability and 20 dB will deliver about 99%
reliability, etc. Multi-path and polarization will affect the link as well. At 2.4 GHz
there is only a small ground wave component involved in the radio propagation,
hence the above numbers presume both clear LOS (line of sight) and clearing at
least 60% of the first Fresnel zone. Multi-path degradation is the reason why a
minimum of 16 to 20 dB of margin is required for the link.
2.3.4 Consideration of other devices in the 2.4 GHz ISM band
The ISM (Industrial, Scientific, and Medical) band at 2.400-2.483 GHz is an
unlicensed band shared for many uses. Any of these devices could become a
source of interference for the Trailblazer products. Some examples are
described here:
Video Transmitters