Page 53
FT-
991
Operating Manual
Interference Rejection
A
B
C
Using IF SHIFT and WIDTH Together
The IF SHIFT and Variable IF WIDTH features
together form a very effective interference-fight
-
ing filtering system.
For example, in Figure “
A
”, you can see how in-
terference has appeared both on the high and low
sides of the desired signal. Touch [
WIDTH
] on
the LCD, the interference from one side can be
eliminated (Figure “
B
”). Next, rotate the
MULTI
knob to re-position the passband (Figure “
C
”),
the interference on the opposite side can be re-
moved, without re-introducing the interference
previously eliminated in Figure “
B
”.
Advice:
The WIDTH and SHIFT features are the pri-
mary 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 yield additional
signal-enhancement benefits on the net residual
bandwidth. Even more, the IF NOTCH Filter
(described later) may also be used, in conjunc-
tion with these filter systems, to significant ad
-
vantage.
Desired Signal
Desired Signal
Desired Signal
QRM
QRM
QRM
QRM
QRM
QRM
IF BANDWIDTH
IF BANDWIDTH
IF BANDWIDTH
WIDTH (IF DSP Bandwidth) Tuning (SSB/CW/RTTY/DATA Modes)
