User's Guide

1313
Antenna Isolation
Isolation between the donor (base) antenna and service area antenna should be 20 dB greater
than the gain of the repeater amplifier.
If the isolation is less than the amplifier gain, then positive feedback sufficient for oscillation is present
in the system. Such oscillations will overdrive one or both amplifier chains and continuously activate
the AGC auto-shutdown circuitry. This situation will be apparent by the red fault LED being lit.
Antenna isolation is usually not a problem for in-building installations. Isolation is improved by using a
directive donor antenna and facing it away from the distribution or service antenna(s). Decoupling is
achieved by spatially separating the antennas vertically and/or horizontally. Other factors influencing
isolation include multi-path reflections, structures, other antennas, passing vehicles, personnel
proximity, etc. Contact RFS Applications Engineering for further assistance.
It is always best to measure the isolation before connecting the repeater. The most direct way to
measure the isolation is to inject a known signal into one antenna, and measure the coupled
signal at the other antenna. This should be done across the applicable bandwidth to account for
the frequency dependency of standing waves.
Diagnostics/Troubleshooting
Test Point Descriptions
• Green power LEDs indicate DC voltage is applied to the respective link.
• Yellow AGC LEDs indicate AGC is active in the respective link
• Red Fault LED indicates that a under or over current condition exists or that the AGC Shut Down
circuitry has been activated.
• Relay NC (normally closed), C (common), NO (normally open) is a summary fault relay that
changes state whenever the fault LED is lit or when the power fails. This relay is rated for up to 48
VDC at 2 Amps.
• Shut Down pin will cause the 48900 to shut down when it is connected to GND (ground). Current
draw is insignificant.
Faceplate
IMPORTANT
The 48900 is not designed for field repair. The outer cover may be removed for some
troubleshooting but under no circumstances should the covers be removed from the
internal amplifier modules, this will void the warranty.