Icom IC-821H Instruction Manual page 26

23
4 RECEIVE AND TRANSMIT
< AGC time constant
The AGC (Automatic Gain Control) controls receiver
gain to produce a constant audio output level even
when the received signal strength is varied by fad-
ing, etc. Use AGC slow for normal phone operation;
AGC fast for receiving data and searching for sig-
nals.
e Push [AGC] to toggle the AGC time constant
between slow and fast.
- The AGC time constant is fixed in FM mode.
The sub band's AGC is automatically selected as
slow in SSB and fast in CW. AGC time constant
cannot be changed in FM mode.
© Attenuator and optional preamp
The attenuator prevents desired signals from dis-
torting when very strong signals are near the desired
frequency or when very strong electric fields, such
as from broadcasting stations are near your location.
e Push [ATT] to toggle the attenuator ON and OFF.
- The attenuation level is approx. 15 dB for each band.
- The attenuator can be used on one band or both
bands using set mode with the [ATT] switch. (p. 49)
O FM center indicator
The RX indicators indicate the received signal devi-
ation in FM mode. When an off-center signal is
received, the RX indicator flashes.
When an off-center signal is received, rotate the
tuning dial or use the RIT function to light the RX
indicator continuously.
The FM center meter can be turned OFF using set
mode with the [FM] switch if desired. See p. 47 for
setting the FM center meter ON and OFF.
The optional preamplifier, AG-25 or AG-35, amplifies
received signals near the antenna to improve the
S/N ratio, sensitivity and cable loss. Turn the pre-
amplifier ON when receiving weak signals.
e Push [PREAMP] to toggle the preamplifier ON and
OFF.
- The preamplifier can be used on one band, both
bands or neither using set mode with the [PREAMP]
switch. (p. 49)
4
The transceiver applies DC voltage to the anten-
nas when this switch is turned ON. Therefore,
this switch should be set to OFF when no pream-
lifier is connected.
Flashes when an off-center signal is received.
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