Yaesu FT-991 Operating Manual page 55

iF notch F
The IF NOTCH filter is a highly effective system that allows cutting out an interfering beat note or other carrier signal
from inside the receiver passband.
1. Press the F(MLIST) button to show the functions
listed on the TFT display.
2. Touch [ NOTCH ] on the TFT display. The Notch
function will be set to "ON".
NOTCH indicator
NOTCH level indicator
3. Rotate the MULTI knob to adjust the "null" position
of the Notch filter.
4. To cancel the NOTCH filter, touch [ NOTCH ] on the
TFT display, "OFF" will appear in the display, con-
firming that the NOTCH filter is no longer in opera-
tion.
A :
dvice
Alternate touches of [ NOTCH ] , will switch the
NOTCH filter between on and off.
A :
dvice
 The bandwidth of the NOTCH filter (either narrow
or wide) may be adjusted using Menu item "116
IF NOTCH WIDTH". The factory default setting is
"WIDE".
FT-991 O
peraTing
i
nterference
o
ilter perAtion
M
anual
( SSb/cW/rtty/dAtA/AM M
The performance of the IF NOTCH filter is illus-
trated in Figure "A", where the desired signal and
the interfering heterodyne are shown within the
IF passband. In Figure "B" the notching effect of
the IF NOTCH filter is illustrated as the MULTI
knob is rotated to eliminate the interfering het-
erodyne.
A
Desired Signal
QRM
(Heterodyne)
IF BANDWIDTH
r
eJection
odeS
F(M-LIST) Button
MULTI Knob
B
Desired Signal
QRM
(Heterodyne)
IF BANDWIDTH
MULTI
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)