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Next Generation
Signal Enhancement
•
There should be adequate vertical & horizontal separation
between the DONOR & SERVER antennas to avoid interference
and noise.
Separation can be determined by the mathematical formulas:
Vertical Separation:
Isolation (dB) = 28 + 40 log (D/
ʎ
in m)
Horizontal Separation:
Isolation (dB) = 22 + 20 log (D/
ʎ
in m) – (Gain of donor antenna
+ gain of server antenna)
D-Distance between donor & server antennas in m
ʎ
- wavelength in m
The following table is an approximate guide to antenna
separation.
The use of highly directional antennas with good front to back
ratios can help to reduce isolation requirements.
VERTICAL ANTENNA
SEPARATION
HORIZONTAL ANTENNA
SEPARATION
Separation (m.)
Isolation (dB)
Separation (m.)
Isolation (dB)
5 75.0 5 45.5
10 87.1 10 51.7
20 99.1 50 65.5
30 106.2 100 71.5
40 111.2 150 75.1
50 115.0 250 77.6
Vertical and Horizontal Antenna Separation @ 900 MHz
The antenna separation table demonstrates that vertical separation yields
better results than horizontal separation. However, when desired isolation
cannot be met due to insufficient separation, external shielding can help; for
example, mounting the antennas on either side of a rooftop penthouse or
using some type of grounded metal screen or wire mesh (so called chicken
wire) between antennas.
The following example illustrates the various signal levels and antenna
gains needed to form a properly functioning repeater system.
Received Signal Level
-72
dBm
Donor Antenna gain
12
dBi
Cable loss (100 ft. of 7/8 inch)
2
dB
Input to Repeater
-62
dBm
Gain of Repeater set
80
dB
Output of Repeater
+18
dBm
Cable loss (100 ft. of 7/8 inch)
2
dB
Server Antenna Gain
9
dBi
Repeater ERP
+26
dBm
