For ‘Rule of 10s and 3s Example 2’
you have a wireless bridge generating
a 100 mW signal. The antenna cable
and connectors create 3 dB of signal
loss, and the antenna provides 10 dBi
of gain.
1
3
10
+
-
*
÷
dBm
0
2
10
mW
1
Start off with the template.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
2
3
10
+
-
*
÷
dBm
0
You determine that by multiplying 1
by 10 twice, you will get 100 mW.
Calculate the new mW value by
performing both of these
multiplications, and enter the new
values in the mW column.
2
10
mW
1
=10
*10
=100
*10
You need to determine if by
using * and ÷ and 2 and 10,
you can change from 1 to 100
mW.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
3
3
10
+
-
*
÷
dBm
0
mW
1
+10
=10
=10
*10
+10
=20
=100
*10
2
10
Remember that whatever you do to one side,
you must do the correlative mathematics on the
other side. Since you multiplied on the right
side, you must add on the left. And since you
multiplied by 10 twice on the right, you must add
10 twice on the left.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
4
+
-
3
10
*
÷
dBm
0
mW
1
+10
=10
=10
*10
+10
=20
=100
*10
-3
=17
2
10
Subtract 3 for the cable
loss.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
5
+
-
3
10
*
÷
dBm
0
mW
1
+10
=10
=10
*10
+10
=20
=100
*10
-3
=17
=50
÷2
2
10
Again, whatever you do to one side, you must do the correlative mathematics on
the other side. Since you subtracted on the left, you must divide on the right. And
since you subtracted 3 on the left, you must divide by 2 on the right. So the IR is
either 17 dBm or 50 mW.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
6
+
-
3
10
*
÷
dBm
0
mW
1
+10
10
10
*10
+10
20
100
*10
-3
17
50
÷2
+10
=27
=500
*10
All that’s left is to increase the dBm
side by the 10 dBi of the antenna.
2
10
When you do, you must perform the
correlative *10 to the mW side.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
7
+
-
3
10
*
÷
dBm
0
mW
1
+10
10
10
*10
+10
20
100
*10
-3
17
50
÷2
+10
27
500
*10
2
10
So you know that the EIRP of this wireless bridge is either 27 dBm or 500 mW. The
two columns of numbers are equal. They are just presented using two different units
of measurement.
Rule of 10s and 3s Example 2: 100 mW bridge, 3 dB cable loss, 10 dBi antenna gain
8