Yaesu VX-450 series, Руководство по обслуживанию

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25 VX-450 Series UHF Band Service Manual
The reference voltage changes into four values
(Transmit Power High and Low) controlled by
Q1040
(
NJM12904V
).
4. PLL Frequency Synthesizer
The frequency synthesizer consists of PLL IC, Q1036
(
AK1541
), VCO, TCXO (X1001).
The output frequency from TCXO is 16.8 MHz and
the tolerance is ±2.5 ppm (in the temperature range
–30 to +60 degrees).
4-1. VCO (Voltage-Controlled Oscillator)
While the radio is receiving, the RX oscillator Q1019
( 2SK508 ) in VCO generates a programmed fre-
quency between 382.35 and 452.35 MHz (Version A:
332.35 and 402.35 MHz) as 1st local signal.
While the radio is transmitting, the TX oscillator
Q1023 ( 2SC4227 ) in VCO generates a frequency be-
tween 400 and 470 MHz (Version “A”) or 450 and
512 MHz (Version “D”).
The output from oscillator is amplified by buffer
amplifier
Q1017 ( 2SC5005 ) and becomes output of
VCO. The output from VCO is divided, one is am-
plified by
Q1022 and feed back to the PLL IC 17 pin.
The other is amplified in Q1014 and in case of the
reception, it is put into the mixer as the 1st local sig-
nal through
D1011 , in transmission, it is buffered
Q1010 , and more amplified in Q1008 and it is put
into the final amplifier Q1008 .
4-2. VCV (Varactor Control Voltage) Control
Tuning voltage of VCO is expanding the lock range
of VCO by controlling the cathode of varactor diode
at the voltage and the control voltage from PLL IC.
4-3. PLL
The PLL IC consists of reference divider, main di-
vider, phase detector, charge pumps and pulse swal-
low operation. The reference frequency from TCXO
is inputted to 10 pin of PLL IC and is divided by
reference divider.
The other hand, inputted feed back signal to 17 pin
of PLL IC from VCO is divided with the dividing
ratio which becomes same frequency as the output
of reference divider. These two signals are compared
by phase detector, the phase difference pulse is gen-
erated.
Circuit Description (Version A & D)
2-5-2. Carrier Squelch
The CPU (14 pin: A/D port) detect RSSI voltage out-
put from
Q1033 12 pin, and controls AF output.
The RSSI output voltage changes according to the
signal strength of carrier. The stronger signal makes
the RSSI voltage to be higher voltage.
The process of the AF signal control is same as Noise
Squelch.
The shipping data is adjusted –1 dBu (EMF) higher
than squelch tight sensitivity.
3. Transmitter System
3-1. MIC Amplifier
The AF signal from internal microphone MC2001 or
external microphone J1004 in to Audio processor IC
Q1013 . (selected 34 pin or 35 pin) Q1013 is which
contains the microphone amplifier, compandor, Pre-
emphasis, limiter and splatter filter, the processed
signal to made FM modulation to transmit carrier
by the modulator
D1014 ( HVC383B ) of VCO.
Q1013 is built-in DTMF Receiver, and Inversion Type
Encryption.
3-2. Drive and Final Amplifier Stages
The modulated signal from the VCO Q1023
( 2SC4227 ) is buffered by Q1017 ( 2SC5005 ) . Then
the signal is buffered by Q1010 (
2SC3356
) for the
final amplifier driver Q1015 ( RQA0004PXDQS ). The
low-level transmit signal is then applied to Q1006
( RQA0011DNS ) for final amplification up to 5watts
output power.
The transmit signal then passes through the antenna
switch
D1005 (
HVU131
) and is low pass filtered to
suppress away harmonic spurious radiation before
delivery to the antenna.
3-3. Automatic Transmit Power Control
The current detector Q1040-1 ( NJM12904V ) detects
the current of Q1006 and Q1008 , and converts the
current difference to the voltage difference.
The output from the current detector
Q1040-1 is com-
pared with the reference voltage and amplified by
the power control amplifier
Q1040-2 .
The output from Q1040-2 controls the gate bias of
the final amplifiers Q1006 and the final amplifier
driver Q1008 .