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— Chapter 3. Mounting the Antennas
PES1900NR Operations Manual
36
Measuring Antenna Isolation
Measure the actual isolation between the antennas, to ensure that the donor (base station) antenna
is sufficiently isolated from the subscriber (mobile) antennas.
WARNING:
This is a critical step in all on-frequency repeater installations.
If the isolation is not sufficient, the repeater might oscillate, or it might operate with less gain (signal
amplification). In the first case, the repeater can introduce spurious emissions into the network. This
is unacceptable. The second case reduces the range of the repeater’s coverage area.
Antenna isolations should be at least 15 dB greater than the repeater gain setting in each direction.
Measuring antenna isolation requires a signal generator and a spectrum analyzer. The generator
transmits a signal from the donor antenna, and the spectrum analyzer measures the same signal as
the subscriber antenna receives it. Figure 6 shows the equipment set-up for each antenna
configuration.
Figure 5 shows four simplified setups. They show only the overall configuration for measuring
antenna isolation. Isolation must take into account all cables that will be attached when the repeater
is in operation. Therefore, you must measure isolation with all jumpers and feeder lines in place. The
only other cables present, that are not part of the actual isolation measurement, should be the one
from the signal generator, and the one to the spectrum analyzer. Figure 6 shows all cables and
equipment in place for measuring actual antenna isolation.