User's Manual
Trailblazer Installation and User Manual version 1.03
6
Some examples are given in the table above. On the software CD that comes with each
system there is a folder called “Calculators”. In that folder you will find an excel
spreadsheet called fresnel zone calculator.xls you can use to calculate your own
path.
Set the Fresnel zone to even numbered values when plotting a profile to see potential
areas of phase canceling present in the path. You can improve your path by optimizing
the height of antennas so that the first Fresnel zone is clear.
2.1.5 Path Loss
After confirming line of sight and adequate Fresnel zone clearance, add the Free Space
Loss of the radio signal, RF cable losses, and antenna gains to determine your system’s
remaining signal, i.e. fade margin. The chart below shows various antenna and distance
combinations.
Distance
in miles
Distance
in km
Ant Gain
in dBi
Ext RF
Cable(s)
Path Loss
in dB
RF power
in dBm
ERP
in dBm
Link Margin
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
You can also calculate your own path loss using the integrated radio link margin
calculator included on the CWT product CD in a folder called “Calculators”.
Video Transmitters
These devices use analog radios which are usually fixed in frequency, utilize 6 to 10
MHz of bandwidth and are low power with an ERP of less then +10dBm.
2.1.6 RF Cable Sizing and Recommendations
Before making any decisions as to which cable to use, first consider several factors; the
final length of the cable, the amount of power you want the cable to tolerate, the loss
factor of the cable at your chosen frequency and the outdoor climate conditions the
cable will be exposed to. For most general installations, LMR400 will work fine. Heliax™