2)
2)
2)
2)F
F
F
Fir
i r
ir
irst
s t
st
stM
M
M
Mi
i
i
ixer
x er
xer
xer
ThesignalfromtheRFamplifierisheterodynedwiththefirstlocaloscillatorsignalfrom
thePLLfrequencysynthesizercircuitatthefirstmixer(Q2)tocreatea26.45MHzfirst
intermediatefrequency(1stIF)signal.ThefirstIFsignalisthenfedthroughcrystalfilters
(XF1,XF2)tofurtherremovespurioussignals.
3)
3)
3)
3)I
I
I
IF
F
F
Fam
a m
am
amp
p
p
plifi
l ifi
lifi
lifier
e r
er
er
ThefirstIFsignalisamplifiedbyQ3,andthenentersU1(FMprocessingIC).The
signalisheterodynedagainwithasecondlocaloscillatorsignalwithinU1tocreatea
450kHzsecondIFsignal.ThesecondIFsignalisthenfedthrougha450kHzceramicf ilter
(CF1)tofurthereliminateunwantedsignalsbeforeitisamplifiedandFMdetectedin
CF1.
4)
4)
4)
4)A
A
A
AF
F
F
Fam
a m
am
amp
p
p
plifi
l ifi
lifi
lifier
e r
er
er
TherecoveredAFsignalobtainedfromU1goestothemicroprocessor(U10).The
processedAFsignalpassesthroughanAFvolumecontrolandisamplifiedtoasufficient
leveltodrivealoudspeakerbyanAFpoweramplifier(U9).
5)
5)
5)
5)Squ
S qu
Squ
Sque
e
e
el
l
l
lch
c h
ch
ch
PartoftheAFsignalfromtheICenterstheFMICagain,andthenoisecomponentis
amplifiedandrectifiedbyafilterandanamplifiertoproduceaDCvoltagecorresponding
tothenoiselevel.TheDCsignalfrom
t
heFMICgoestotheanalogportofthe
microprocessor(U10).U 10determineswhether
t
ooutputsoundsfromthespeakerby
checkingwhethertheinputvoltageishigherorlowerthanthepresetvalue.
6)
6)
6)
6)R
R
R
Rece
e ce
ece
ecei
i
i
iv
v
v
ve
e
e
es
s
s
si
i
i
ign
g n
gn
gna
a
a
ali
l i
li
lin
n
n
ng
g
g
g
QT/DQT
TheoutputsignalfromFMIC(U1)entersthemicroprocessor(U10).U810determines
whethertheQTorDQTmatchesthepresetvalue,andcontrolstheAFPowerandthe
speakeroutputsoundsaccordingtothesquelchresults
3
3
3
3.
.
.
.P
P
P
PLL
LL
LL
LLf
f
f
fr
r
r
re
e
e
equ
q u
qu
que
e
e
en
n
n
nc
c
c
cy
y
y
ys
s
s
sy
y
y
yn
n
n
nt
t
t
th
h
h
hes
e s
es
esiz
i z
iz
ize
e
e
er
r
r
r
ThePLLcircuitgeneratesthefirstlocaloscillatorsignalforreceptionandtheRFsignalfor
transmission.
1)
1)
1)
1)PL
P L
PL
PLL
L
L
L
ThefrequencystepofthePLLcircuitis5and6.2
5
kHzandsoon.A13MHzreference
oscillatorsignalisdividedatU4byafixedcoun tertoproducethe5or6.25kHz
referencefrequency.Thevoltagecontrolledoscillator(VCO)outputsignalisbuffer
amplifiedbyQ15,thendividedinU4byaprogrammablecounter.Thedividedsignalis
comparedinphasewith
t
he5or6.25kHzreferencesignalinthephasecomparatorin
U4.Theoutputsignalfromthephasecomparatorisfiltreredthroughalow
-
passfilter
andpassedtotheVCOtocontroltheoscilla
t
orfrequency.
2)
2)
2)
2)VC
V C
VC
VCO
O
O
O
TheoperatingfrequencyisgeneratedbyQ12intransmitmodeandQ19inreceive
mode.TheoscillatorfrequencyiscontrolledbyapplyingtheVCOcontrolvoltage,obtained
fromthephasecomparator, tothevaractordiodes(
D
8andD12intransmitmodeand
D11andD13inreceivemode).TheTC/
R
CpinissetlowinreceivemodecausingQ13off,
TheTC
/
RCpinissethightintransmitmodecausingQ14off.
