FIPLEX • Electromagnetic Devices for Radiocommunication Systems
FIPLEX BIDIRECTIONAL AMPLIFIER - USER MANUAL
If “AGC ON” led indicator is on when the repeater starts operating, this means that
signal received from the donor site is above minimum signal level required for nominal
gain operation so AGC circuitry is active.
Under this condition of operation user should attenuate the gain level of the
repeater using DOWN control, decreasing gain until “AGC ON DOWNLINK” indicator turns
off.
This operation is recommended in order to release dynamic range to the AGC
circuitry.
Automatic Gain Control (AGC)
Automatic Gain Control circuitry is intended to keep repeater’s output power at a
fixed level when input signals exceed maximum values, avoiding quality signal degradation
by intermodulation generation.
If “AGC ON Downlink” led is on this means that signal level from donnor site plus
repeater gain produces an output power that is above the maximum composite output
power of the repeater. This should not be considered an undesired working condition, far
from that; this is the best operating condition because you are getting the maximum
composite output power available from the repeater.
Anyway is a good practice (if manual attenuator is set to a value different from
zero), to increase attenuation (reducing gain), until AGC led turns off, this operation
releases AGC circuitry dynamic range.
Also is a good practice to check signals from donor site to ensure that undesired
signals are not being amplified by the repeater, or even desired signal levels are not
excessively high taking repeater to an overload condition.
Overload Protection
When the automatic gain control circuit reaches its limit (20 dB), the power
amplifier stage is shut down to prevent harmful distortion and potential damage to the
repeater. After approximately ten seconds the system checks if overload condition is still
present, if this happens amplifiers will remain off. This cyclic check will continue until
condition that makes AGC circuitry reach its limits desapears.
Conditions that can cause AGC to reach its limits include the presence of one or
more very strong channels, a strong in-band noise source, or amplifier oscillation due to
poor antenna isolation.
When overload protection is active led labeled “OVERLOAD DOWNLINK” is on.
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Document FIP-BDAM-07-EN
