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Page 44 FT-991 OperaTing Manual
convenience features
receiver operAtion
(
Front end block diAgrAM
)
The
FT-991
includesawiderangeofspecialfeaturestosuppressthemanytypesofinterferencethatmaybeencoun-
teredontheHFbands.However,realworldinterferenceconditionsareconstantlychanging,sooptimumsettingofthe
controlsissomewhatofanart,requiringfamiliaritywiththetypesofinterferenceandthesubtleeffectsofsomeofthe
controls. Therefore, the following information is provided as a general guideline for typical situations, and a starting
point for your own experimentation.
The
FT-991
interference-ghtingcircuitrybeginsinits“RF”stages,andcontinuesthroughouttheentirereceiversec-
tion.
FT-991
allowscongurationofthefeaturesdescribedbelow.
CONTOUR Filter
TheDSP Contourfilter hastheunique abilitytopro-
vide eithera null ora peak intunablesegments of the
receiverpassband.You maysuppress interferenceand
excessivefrequencycomponentsofanincomingsignal,
oryoumaypeakthosetunablefrequencysegments.The
levelofthenullorpeak,andthebandwidth,overwhich
itisapplied,areadjustableviatheMenu.
IF SHIFT
ThepassbandcenterfrequencyoftheIFDSPltermay
bemovedupordownbyadjustingthiscontrol.
IF WIDTH
ThewidthoftheIFDSPlteringmaybeadjustedusing
this control.
IF NOTCH
TheIFNotchlterisahigh-Qnotchlterthatcanelim-
inate,orsignicantlyreduceaninterferingcarrier.
DNF
(
Digital Notch lter
)
When multiple interfering carriers are encountered dur-
ingreception, theDigital NotchFilter cansignicantly
reduce the level of these signals.
DNR
(
Digital Noise Reduction
)
TheDSP’s DigitalNoiseReduction (DNR)feature uti-
lizes 15 different mathematical algorithms to analyze
andsuppressdifferentnoiseprolesencounteredonthe
HF/50 MHzbands. Choose the selectionthat provides
thebestnoisesuppression,andallowsthesignaltorise
up out of the noise.
AGC
The AGC system automatically adapts to changing sig-
nalandfadingcharacteristics,makingreceptionpossible
underthemostdifcultconditions.
The
FT-991
usesthe15kHzroonglteronAM/
FM/C4FM modes. All the other modes use the
3 KHz filter automatically. There is no manual
selectionpossible.
Front end block diAgrAM
HF/50MHz
HF/
50MHz
ANT
VHF/
UHF
ANT
ATT BPF
RF
1st IF
69.450 MHz
2nd IF
9 MHz
2nd IF
450 kHz
FM C4FM
3rd IF
24 kHz
MCF
144MHz
LPF
430MHz
LPF
BPF
RF AMP/
IPO
1st
IF AMP
3rd
IF AMP
DSP
UNIT
ROOFING
FILTER
RF AMP
RF AMP BPF FM DET
1st Local
3 kHz
15 kHz
2nd Local
3rd Local
1st Local
2nd Local
C4FM
DSP UNIT
46


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