Sailor RE2100, Техническое руководство

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3 SERVICE RE2100
Below the threshold level the input signal is too weak to be detected by the AGC circuit. The gain of the
2nd IF amplifier is then unregulated and the receiver output level will increase as 1:1 with increasing input
level.
Above the threshold level the input signal is large enough to be detected by the AGC. The gain of the 2nd
IF amplifier will then be regulated and the output from the receiver will idealistically be kept at a constant
level. However, in practice the receiver output level will increase slightly with increasing input level,
because a constant output level would require an infinite gain of the 2nd IF amplifier.
The performance of the AGC above the threshold level is checked by measuring the “flatness” of the AGC
characteristic. This measurement is also included in the check procedure given below, because it is
measured in the same manner as the threshold level.
The threshold level must, as indicated in the AGC characteristic, be less than the sensitivity level of the
receiver to ensure correct function of the AGC. The threshold level is determined by the level detector
and the open loop gain from the aerial input to the level detector input. To study this in more details, the
simplified block diagram is used in the following description.
4-0-26212
Simplified block diagram for the entire receiver.
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