Yaesu FT-991 Operating Manual

Also see for FT-991: Manual Manual Operating manual Reference book Instruction manual

Page 40FT-991 O PERA T ING M ANUALA B CinTerferenCe reJeCTionwidth (iF dSp bAndwidth) tuning (SSb/cw/rtty/dAtA ModeS)The IF WIDTH tuning system allows you to vary the width of the DSP IF passband, to reduce or eliminate interference.Moreover, the bandwidth may actually be expanded from its default setting, should you wish to enhance incoming sig-nal fidelity when interference on the band is low.1. Touch [WIDTH] displayed by pressing the F(M-LIST) button repeatedly to reduce the interference.A dvice :The frequency display will show the bandwidth ofthe IF passband whenever [WIDTH] is touched.Referring to Figure “B”, you can see the defaultbandwidth on the SSB mode.By rotating the MULTI knob to the left, the band-width will narrow (see Figure “A”, while rotationof the MULTI knob to the right, as depicted inFigure “C”, will increase the bandwidth.A B CThe default bandwidths, and total bandwidth ad-justment range, will vary according to the operat-ing mode:SSB Mode: 1.8 kHz ~ 4.0 kHz (default: 2.4 kHz).CW Mode: 500 Hz ~ 2.4 kHz (default: 2.4 kHz)RTTY/DATA Modes: 500 Hz ~ 2.4 kHz (default:500 Hz)Using IF SHIFT and WIDTH TogetherThe IF SHIFT and Variable IF WIDTH featurestogether 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 lowsides of the desired signal. Touch [WIDTH] onthe LCD, the interference from one side can beeliminated (Figure “B”). Next, rotate the MULTIknob to re-position the passband (Figure “C”),the interference on the opposite side can be re-moved, without re-introducing the interferencepreviously eliminated in Figure “B”.A dvice:For best interference reduction, the WIDTH andSHIFT features are the primary tools you shoulduse, after narrowing the bandwidth (WIDTH)and/or adjusting the center of the passband(SHIFT). The Contour control may then yieldadditional signal-enhancement benefits onthe net residual bandwidth. Even more, the IFNOTCH Filter (described later) may also beused, in conjunction with these filter systems, tosignificant advantage.IF BANDWIDTH IF BANDWIDTH IF BANDWIDTHMULTI MULTI MULTI Desired Signal Desired Signal Desired SignalQRMQRMQRMQRMQRMQRMIF BANDWIDTH IF BANDWIDTH IF BANDWIDTHF(M-LIST) Button