Yaesu FT DX 1200, Руководство по эксплуатации

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Page 61
FT
DX
1200 O
PERATING
M
ANUAL
AGC
(
A
UTOMATIC
G
AIN
C
ONTROL
)
The $ GC system is designed to help compensate for fading and other propagation effects. The $ GC characteristics can
be individually set for each operating mode. The basic objective of $ GC is to maintain a constant audio output level
once a certain minimum threshold of signal strength is achieved.
3 ress the [ AGC
] button repeatedly to select the desired
receiver-recovery time constant. You will observe the
$ GC status notation in the $ GC column of the . ey
Function ' isplay on the TFT display, denoting the $ GC
receiver-recovery time currently in use. For most opera-
tions, we recommend the “
$ UT 2 ” mode. $ dditionally,
you may disable the $ GC by pressing and holding in the
[
AGC
] button for one second.
T
OOLS FOR
C
OMFORTABLE AND
E
FFECTIVE
R
ECEPTION
[AGC] Button
N
OTE
:
ˆ The “ $ UT 2 ” selection mode selects the optimum
receiver-recovery time for the reception mode.
In this case, the selected receiver-recovery time in
the $ GC column of the . ey Function ' isplay glows
green 1 ormally glows blue).
ˆ
3 ressing the [
AGC
] button allows selection of the
desired receiver-recovery time constant. 1 ormally,
the “ $ UT 2 ” 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 F
$ ST. The $ UT 2
mode selections are
A
DVICE
:
ˆ If the $ GC receiver-recovery time is set t o “ 2 ff” by
pressing and holding in the [ AGC
] button, the S-
meter will no longer de À ect. $ dditionally, you will
likely encounter distortion on stronger signals, as the
IF ampli
¿ ers and the following stages are probably
being overloaded.
Q
UICK POINT
:
Several aspects of $ GC performance may be con ¿ gured
via the 0 enu. However, because $ GC can have such a
profound impact on overall receiver performance, we
generally do not recommend any changes to the
$ GC
0 enu selections until you are thoroughly familiar with
the performance of the FT
DX
1200 .
T
ERMINOLOGY
:
$ utomatic Gain Control, or $ GC, is a circuit that senses
the received signal strength, and then limits the gain of
the
5 F and IF stages to keep the output audio volume at
a more-or-less constant level. $ GC also protects the 5 F,
IF, $ udio, and ' S 3 stages from overload, as it limits the
signal strength that is allowed to À ow, irrespective of the
input signal level.
AUTO AGC S
ELECTION
SLOW
FAST
MID
O
PERATING
M
ODE
LSB/USB/AM
CW/FM
RTTY/DATA
SLOPED AGC Operation
In traditional $ GC systems, the audio output from the transceiver becomes essentially ¿ xed once the threshold
for $ GC action is reached usually several do ] en dB above the no-signal noise À oor). The
FT
DX
1200
, however,
includes an innovative Sloped $ GC system on the 0 ain band VF 2 - $ ) receiver, that allows the audio volume
to rise and fall slightly according to signal strength. $ lthough the rise fall slope is not dramatic, it is suf ¿ cient to
allow you to use your ear to discern and separate signals according to signal strength, not just audio fre T uency.
Using Sloped $ GC
1. 3 ress the [ MENU
] button to engage the
0 enu mode.
. 5 otate the [ VFO-B/CLAR
] knob
or press the S T
button) to select 0 enu item “
004 AGC SLOPE
”.
3. 3 ress the [ SELECT
] button, then rotate the [
VFO-B/
CLAR
] knob
or press the S T button) to change the
setting to “SL 23( ”.
4. 3 ress the [ SELECT
] button, then press the [
MENU
] but-
ton to lock in the new setting and exit to normal opera-
tion.You will now be using the Sloped
$ GC system.
SLOPED
NORMAL
AGC start
Input Signal
Audio Output
K
EY
F
UNCTION
D
ISPLAY
Indicates the AGC