Agc ( Automatic Gain Control ) - Yaesu FT-991A Operating Manual

Tools for Comfortable and Effective Reception
The AGC system is designed to help compensate for fading and other propagation effects. The AGC characteristics can
be individually set for each operating mode. The basic objective of AGC is to maintain a constant audio output level
once a certain minimum threshold of signal strength is achieved.
Press the F ( M-LIST ) button, then touch [ AGC ] on the
LCD repeatedly to select the desired receiver-recovery
time constant. You will observe the AGC status notation
in the AGC column of the Key Function Display on the
TFT display, denoting the AGC receiver-recovery time
currently in use. For most operations, we recommend
the "AUTO" mode. Additionally, you may disable the
AGC by touching [ AGC ] on the LCD.
Note:
 The "AUTO" selection mode selects the optimum
receiver-recovery time for the reception mode.
In this case, the selected receiver-recovery time in
the AGC column of the Key Function Display glows
green ( Normally it glows blue ) .
 Touching [ AGC ] on the LCD allows selection of the
desired receiver-recovery time constant. Normally,
the "AUTO" selection is satisfactory for most situ-
ations, but in the event of operation on a crowded
band where you wish to receive a weak signal, you
may wish to change the setting to FAST. The AUTO
mode selections are:
Operating Mode
LSB/USB/AM
CW/FM/DATA-FM
RTTY/DATA-LSB/DATA-USB
FT- 991 Operating Manual

AGC ( Automatic Gain Control )

AUTO AGC Selection
SLOW
FAST
MID
F ( M-LIST ) Button
Advice:
 If the AGC receiver-recovery time is set to "Off" by
touching [ AGC ] on the LCD, the S-meter will no
longer deflect. Additionally, you will likely encoun-
ter distortion on stronger signals, as the IF amplifiers
and the following stages are probably being over-
loaded.
Quick point:
Several aspects of AGC performance may be configured
via the Menu. However, because AGC can have such a
profound impact on overall receiver performance, we
generally do not recommend any changes to the AGC
Menu selections until you are thoroughly familiar with
the performance of the FT-991A.
Terminology:
Automatic Gain Control, or AGC, is a circuit that senses
the received signal strength, and then limits the gain of
the RF and IF stages to keep the output audio volume at
a more-or-less constant level. AGC also protects the RF,
IF, Audio, and DSP stages from overload, as it limits the
signal strength that is allowed to flow, irrespective of the
input signal level.
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