Kenwood TH-77A Service Manual page 9

In the transmit signal channel, a directly oscillated voltage-con- The voltage-controlled OUTBUTS for the VHF and CHE pends ale
trolled oscillator (VCO) signal for the VHF and UHF bands is sent to two-stage amplifiers, then amplified to the reaniied
sent to the reactance modulator. The output levels of the mi-
level by the RF power amplifier module. The amplified output
crophone amplifiers for the VHF and UHF bands can be adjust-
signals are passed through the antenna switches for the VHF
ed independently. (See Figure 5.)
and UHF bands, and sent through a duplexer and lowpass filter
3-1 Modulator Circuit to the antenna.
The audio signal from the microphone is sent to control unit !C1
(NJM4560M), then a preemphasis circuit, amplifier, limiter am-
plifier, and splatter filter. The signal is then selected for the VHF
and UHF bands by Q12. The frequency deviation can be adjust-
ed by VR3 and VR4. The modulation signal is applied to a vari-
cap diode for voltage-controlled oscillator modulation for the
VHF and UHF bands, then sent to the reactance modulator.
The input pins are jumpered by Q11 when a dual-tone multifre-
quency (DTMF) is used.
144 MHz band
430 MHz band
Low frequency VCO (VHF) Buffer Buffer Excitation Excitation
esis 25238 (KI) rae oe sao (ee SAva24
NJM4560M
284083
28C4083
2SCA215 2SC3356
S-AV22A
Buffer
amplifier
2S8C4215
PLL eu
amplifier
M56760FP 2SC4116
CPU
#PD751 |6GF
HD404608
PLL
M56760FP
Buffer
amplifier
28C4226
REF OSC
2804116
Fig. 5 Transmitter system block diagram