User's Manual

Advanced RF Technologies, Inc.
24
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 can be attained by separating antennas at 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.
With ICS mode, the recommended isolation value is 5dB greater than the maximum gain of the repeater. For
example, if the gain of the repeater is 50 dB, then an isolation of 55dB or greater is required. In the same manner,
because the AXM700F-9543-ICS-X has a maximum gain of 95dB in case of AXM700F-9543-ICS-X, it requires
isolation of at least 100dB.
With SDR mode, the recommended isolation value is 20dB greater than the maximum gain of the repeater. For
example, if the gain of the repeater is 50 dB, then an isolation of 70dB or greater is required. In the same manner,
because the AXM700F-9543-ICS-X has a maximum gain of 95dB in case of AXM700F-9543-ICS-X, it requires
isolation of at least 115dB.
WARNING: Inserting a CW signal into the AXM700F-9543-ICS-X when ICS is enabled will cause the system to
generate a false alarm. The false alarm will cause the system to go into a shutdown state. If a CW signal needs to
be injected into the repeater for testing purposes, the ICS routine must be turned off.