User's Manual

Advanced RF Technologies, Inc.
27
4.2 Antenna Separation/Isolation
The separation between the donor and server antennas is necessary to prevent oscillation. Oscillation occurs
when the signal entering the system continually re-enters, 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 4-2 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.
Recommended isolation value is 15dB greater than the user-set gain of the repeater. For example, if the user-
set gain of the repeater is 50dB, then an isolation of 65dB or greater is required. In the same manner, to utilize
the maximum gain of 95dB of the PSR-78-9533, an isolation of at least 110dB is required.
PSR-78-9533