\/. \'ARACTOR TUNER
AND PRESET TUNING SYSTEM
I. VARACTOR TUNER
Avaractortuneristh€lunersystem
inwhich
varáctor
diode
junction
capacitanceisvariedbymeansof the
inversebiasvalueappliedto the diodefor station
selection. By employinga varactor
diode.
tuning
which is samea! ordinaryvaÍiablecondenseÍs),stem
cánbêmad€
withoutusinga variablecondenserby
changingcontrol
voltageonly.
l) Features
a) Whenusedin an FM tuner,th€ front endcan
be madesmall€rthan\{hencompaÍedwith a
variablecondenser.
b) Station selectorbutaonpositioning
is not
limited.
c) Slation sel€ctionby remotecontrol ispossible.
d) Idealvoltagecanbe setfor a certainreception
frequencybeforehand,and presettuning can
b€ efect€d by successively
switching the
e) If control voltsg€ sweep is at ideal speed,
automatictuning(seàÍchtuning)isposible-
0 Pow€r consumption is about the same as a
variablecondenseÍsystem.
ï
f,
g
q
Fig.3
Fig.4 TuningcircuitemployingavaÍactordiode
Fig.5 ExampleofHighFrequency
AmplifierStage
Cncuit
+ INVERSEVOLTÀCE
2) VaÍactor
Diode
Characteristics
As foÍ varactor
diodecharacteristics,
asshown
in Frg.3, cápacitancec r( changedby chm8e
in
inversevoltage
VR. Further,
ifthis varactor
diode
isused
jnatuningcircuit,
the
followingconditions
Cmax + CD
Cmin + CD
Cmai, Cmin arc th€ maximum and minimum
valuesof varactordiode capacitánce
change. CD
is the sum of stray capacitance
and trinmer
capacitance.
K isover
l_5
b€causeFMbroadcast
frequency
rangeis 88 to t08 MHa Fig.s4(a)
and
4(b) showtheactualusage
method.
I
