User's Manual

Advanced RF Technologies, Inc. 23
4.3 Antenna Separation/Isolation
Separation between the antennas is necessary to prevent oscillation. Oscillation occurs when the signal
entering the system continually reenters, due to the lack of separation between the donor and server antennas. In
other words, the signal is being fed back into the system. This creates a constant amplification of the same signal.
As a result, the noise level rises above the signal level.
Figure 4-3 RF Repeater Oscillation
To prevent feedback, the donor and server antennas must be separated by an appropriate distance to provide
sufficient isolation. Isolation is attained by separating antennas a sufficient distance so that the output of one
antenna does not reach the input of the other. This distance is dependent on the gain of the repeater.
A sufficient isolation value is 15 ~ 20dB greater than the maximum gain of the repeater. For example, if the
gain of the repeater is 50 dB, then an isolation of 65 ~ 70dB or greater is required. In the same manner, because
the AXM700-9543 has a maximum gain of 95dB in case of AXM700-9543, it requires isolation of at least 110 ~
115dB.