Kenwood TKR-D710 Service Manual Download

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TKR-D710

2-3. Transmitter Main PLL circuit (SUB unit)

■

VCO

The TX VCO circuit consists of two VCOs (VCO A X58-

520: Q352, VCO B X58-520: Q353). Those VCOs generates
a transmit carrier. VCO A Q352 produces a transmitter fre-
quency from 136.000MHz to 154.995MHz. VCO B Q353
produces a transmitter frequency from 155.000MHz to
174.000MHz.

Those VCO oscillation frequencies are determined by

two systems of voltage control terminals: “CV” and “TXAS-
SIST”.

The voltage control terminals, “CV” and “TXASSIST”, are

controlled by the PLL IC (X58-520: IC300) and MCU (X53-
458: IC20) and the output frequency changes continuously
according to the applied voltage. For the modulation input
terminal, “MO”, the output frequency changes according to
the applied voltage.

D355

D352

D358

D359

SW Q350

TXVCOA

TX_CV

TXASSIST

TXVCOB

80C

VCO_A

Q352

Buffer

Q354

SW Q351

D357

D353

D360

D361

VCO_B

Q353

Fig. 3 Transmitter VCO circuit

■

PLL IC (X58-520: IC300)

The PLL IC compares the differences in phases of the

VCO oscillation frequency and the transmitter PLL reference
signal (16.8MHz), returns the difference to the VCO CV ter-

minal and realizes the “Phase Locked Loop” for the return
control. This allows the VCO oscillation frequency to accu-
rately match (lock) the desired frequency.

When the frequency is controlled by the PLL, the fre-

quency convergence time increases as the frequency dif-
ference increases when the set frequency is changed. To
supplement this, the MCU is used before control by the
PLL IC to bring the VCO oscillation frequency close to the
desired frequency. As a result, the VCO CV voltage does not
change and is always stable at approx. 3.0V.

The desired frequency is set for the PLL IC by the MCU

(X53-458: IC20) through the 3-line “SPSD0”, “SPSCLK0”, “/
TXPCS” serial bus. Whether the PLL IC is locked or not is
monitored by the MCU through the “LDT” signal line. If the
VCO is not the desired frequency (unlock), the “LDT” logic
is low.

Ref 16.8MHz

LDT

SPSCLK0

SPSD0

/TXPCS

Buffer

Q300

TX VCO/PLL

IC300

LPF

TX_CV

BPF

FIN

Loop filter

Fig. 4 Transmitter Main PLL IC circuit

2-4. Modulation level adjustment circuit

The Modulation level adjustment circuit adjusts the mod-

ulation waveform balance. This circuit consists of IC804,
IC603, IC604, IC605 and IC606.

The modulating signal comes from the Control unit (X53-

458) through the interface connector (CN800 Pin 14). The
modulating signal is produced by the modulation low-pitched
tone to the transmitter modulation 16.8MHz PLL circuit and
adds the high-pitched modulation to the transmitter main
PLL.

IC804 is an electronic volume control IC. It has 8 elec-

tronic volume control circuits. The modulation level adjust-
ment circuit uses 2 electronic volume control circuits in
IC804. The 1st electronic volume control circuit adjusts the
modulating signal and is fed to IC603 and the 2nd electronic

Fig. 2 Transmitter reference 16.8MHz PLL circuit

TX VCO

/PLL

MOD

PLL IC

X58-5200-10

Ref
19.2MHz

LDT

IC602

SPSCLK0

SPSD0

/16_8PCS