32
Interference Rejection
FT-891 Advance Manual
IF NOTCH Filter Operation (SSB/CW/RTTY/DATA/AM Modes)
The IF NOTCH filter is a highly effective system that can reduce or eliminate an interfering
beat note or other carrier signal from inside the receiver passband.
1. Press the [
F
] key repeatedly, to find the
“FUNCTION-1” list screen.
2. Rotate the
MULTI
function knob to select
“NCH”.
3. Press the
MULTI
function knob, and then
rotate it to adjust the “null” position of the
Notch filter within the receiver passband.
4. When the adjustment is completed, press
the
MULTI
function knob.
5. Press and hold the [
F
] key for one second
to exit the “FUNCTION-1” list screen and re-
sume normal operation.
r
To set the IF NOTCH to “OFF”:
1. Press the [
F
] key repeatedly, to find the “FUNCTION-1” list screen.
2. Rotate the
MULTI
function knob to select “NCH”, then press the
MULTI
function knob.
3. Press and hold the [
F
] key for one second to exit the “FUNCTION-1” list screen
and resume normal operation.
r
The bandwidth of the NOTCH filter (either narrow or wide) may be adjusted using
Menu item
“
12-04
[
IF NOTCH WIDTH
]”
. The factory default setting is “WIDE”.
r
IF NOTCH function may be assigned to the [A], [B] or [C] key. Refer to “Changing the
function assigned to the [A]/[B]/[C] keys” in the FT-891 Operating Manual.
The performance of the IF NOTCH
filter is illustrated 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 illus-
trated as the MULTI knob is rotated to
eliminate the interfering heterodyne.
(A)
(B)
IF BANDWIDTH
IF BANDWIDTH
MULTI
Desired Signal
Desired Signal
QRM
(Heterodyne)
QRM
(Heterodyne)
