Transmitter System; Microphone Amplifier; Final Amplifier; Apc Circuit - Kenwood TK-768 Service Manual

)
a
)
)
3-2. Finalamplifier
The signal from the PLL is amplified by drive ampli-
fier (0205, 206) and power module (1C501) to an out-
put level of 25W45W, and goes through the antenna
switch D20 and harmonic filter, and on to the antenna
terminal.
lC13 filzl compares the DC input to pin 2 with the
reference voltage at pin 3 applied by ICB (1/2), ampli-
fies the result, and controls the DC amplifier (Q22 and
O23) to keep the transmit final current constant, thus
keeping the transmit output constant.
3-3. APC circuit
The direct current that flows through the power
module (1C501) produces a voltage across resistors
R108. This voltage is applied to pin 6 of lC13 l2l2l, and
is input as the reference voltage difference of pin 5 and
amplified.
)
)
)
CIRCU IT D ESCRI PTIO N/ FE ffiË HN
3.Transmitter System
3-1. Microphone amplifier
The signalfrom the microphone goes to the micro
phone mute Switch (Q403 off), lt then passes through
the high-pass filter in 1C402 (212l. and the pre-empha-
sis/lDC circuit in 1C402 (1121.
The signal is applied to the 1C404 summing amplifier
and mixed with OT from the CPU (1C409). lt then
passes through the splatter filter (the fourth low-pass
filter) consisting of 1C406 (112,212]',
which removes
unwanted harmonics.
The output from the low-pass filter is input to the D/
A converter (lC6)to adjust the modulation.
From
Microphone
Fig. 3 Microphone ampliÍication
3-2. tfrË*ËË
* É t r f H 4 ( P L L ) É t Ë € É H f f i È t J t á #
( Q205,Q206
) ffi t, f*F+i fr.^X&Írt+fr Jt+Ffr t U
D 20 fr iHWlg&{F,Ëftiá*ffi tr
"
rc13 ( u2) ffiffi 2 HÊ!Éffiffi^ÊEfiÉ rc8 (1/
2) E L+g|ffi 3 WffJ4t HE+E bh&, tL#.Ê<J**
*Wffi.
x, Mffiwfif{à€, Ëft||ËffitrJt# (Q22frrq.,;3)
, t))
4*W È.W Xetrt # É! Êifi Êg E Ë.
3-3. Ê drdr*Hf;tlËffi ( A P c )
ffi,firrt 4lffiWÊlHffi Èffi ê Rl08 Ê,ffi. mffi È4 - f
ÉE, ÉLË,EfigJ rc13 (2n) WH 6m, +f[ 5ffJ4t
Ttc768/H
3. ËSJËF
3-1. iËÊfft*+E
ÁiÉÉrffi ^ Êt È ffitr'" Et$tiÉ ffi ffi È#x ( Q403&
Jt') tr^É rc402 Qn) &frÊ!ËjÉtË&**, iáiÍtË&
ffi f=" E& rc402 ( U2) fr:frffilnÉ,/ wffiffi.t ( rDc Ê,
ffi ) 4I4.
,ái$414 Ê!{È€& jË^ rc404 Ê! il Ëtrn{*ft * Ê
cpu lÍ crcss uÈfrË€lEê , f E jEi$ fr rc4061n,2l
2) t6frÊ!{ÍiËffiw{# ( ffi 4 {ftiÉ}B** ) uffihfttrÉ0*
ffi{Ë€.
iEi$Í{ftiÉffiw#É0{àëË^ D/A 4&# ( rc6 ) D{
iEHiEfi{Ë.
D/A Converter
tc6
Fig. 4 Transmit power circuit and APG circuit
39