Antenna Separation/Isolation; Figure 4-7 Rf Repeater Oscillation - ADRF SDR User Manual

4.3 Antenna Separation/Isolation/ Installation
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.
The Donor antenna cable must be used with 24 dB Loss.
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 SDR
has a maximum gain of 95dB in case of SDR-33, it requires an isolation of at least 108 ~ 110dB.
Advanced RF Technologies, Inc.
Figure 23 RF Repeater Oscillation
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SDR-33-AF