User's Manual

AXM700 Repeater
User Manual V0.2
Page | 16
3.4.4 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 6: 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 13 ~ 15 dB greater than the maximum gain of the repeater. For example, if the gain of the repeater is
50 dB, then an isolation of 63 ~ 65 dB or greater is required. In the same manner, because the AXM700 has a maximum gain of
90 dB in case of AXM700, it requires an isolation of at least 103 ~ 105 dB.