31
Interference Rejection
FT-891 Advance Manual
Using IF SHIFT and WIDTH Together
The IF SHIFT and Variable IF WIDTH features, together, form a very effective interference
fighting filter system.
For example, in Figure (A), interference has
appeared on both the high and low sides
of the desired signal. By enabling the IF
WIDTH Operation, the interference from
one side can be eliminated (Figure “B”).
(A)
(B)
(C)
IF BANDWIDTH
Desired Signal
QRM
QRM
Desired Signal
Desired Signal
IF BANDWIDTH IF BANDWIDTH
QRM
QRM
QRM
QRM
Next, rotate the
MULTI
function knob to re-position the passband (Figure (C)), the in-
terference on the opposite side can be removed, without re-introducing the interference
previously eliminated in Figure (B).
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The WIDTH and SHIFT features are the primary tools to use for best interference
reduction. After narrowing the bandwidth (WIDTH) and/or adjusting the center of the
passband (SHIFT), the Contour control may then be activated to provide additional
signal-enhancement benefits on the net residual bandwidth. Even more, the IF NOTCH
Filter (described later) may also be used, in conjunction with these filter systems, to
significant advantage.
NARROW (NAR) One-Touch IF Filter Selection
1. Press the [
F
] key repeatedly, to find the
“FUNCTION-1” list screen.
2. Rotate the
MULTI
function knob to select
“NAR”.
3. Press the
MULTI
function knob to enable
one-touch, selection of the mode-specific,
narrow IF DSP filter, that does not require
resetting the WIDTH/SHIFT bandwidth con-
trol.
4. Pressing the
MULTI
function knob once more returns the bandwidth control to the
WIDTH/SHIFT system.
The factory default bandwidths are:
Operating Mode
Enable/Desable the NARROW Function
Enable
Desable
SSB
200 Hz - 1.8 kHz* (1.5 kHz)
1.8 - 3.2 kHz* (2.4 kHz)
CW
50 - 500 Hz* (500 Hz)
500 Hz - 3.0 kHz* (2.4 kHz)
RTTY/DATA (LSB, USB)
50 - 500 Hz* (300 Hz)
500 Hz - 3.0 kHz* (500 Hz)
AM
6 kHz
9 kHz
FM/DATA (FM)
9 kHz
16 kHz
*: Depends on the [WIDTH] setting / ( ): Default Bandwidth
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NARROW 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.
