Circuit Description (Version I & K); Vx-450 Series Uhf Band Service Manual - Vertex Standard VX-450 series Service Manual

Circuit Description (Version I & K)
When the detection voltage is low, the CPU makes
Q3049 ON with making 90 pin "H" and the AF sig-
nal is output.
2-5-2. Carrier Squelch
The CPU (14 pin: A/D port) detect RSSI voltage out-
put from Q3033 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 –1dBu (EMF) higher
than squelch tight sensitivity.
3. Transmitter System
3-1. MIC Amplifier
The AF signal from internal microphone MC2001
(Non key Type: MC3001) or external microphone
J3004 in to Audio processor IC Q3013 (selected 33
pin or 34 pin). Q3013 is which contains the micro-
phone amplifier, compandor, Pre-emphasis, limiter
and splatter filter, the processed signal to made FM
modulation to transmit carrier by the modulator
D3014 (HVC383B) of VCO.
Q3013 is built-in DTMF Receiver, and Inversion Type
Encryption.
3-2. Drive and Final Amplifier Stages
The modulated signal from the VCO Q3023
(2SC4227) is buffered by Q3017 (2SC5005). Then
the signal is buffered by Q3010 (2SC3356) for the
final amplifier driver Q3015 (RQA0004PXDQS). The
low-level transmit signal is then applied to Q3006
(RQA0011DNS) for final amplification up to 5 watts
output power.
The transmit signal then passes through the antenna
switch D3005 (HVU131) and is low pass filtered to
suppress away harmonic spurious radiation before
delivery to the antenna.

VX-450 Series UHF Band Service Manual

3-3. Automatic Transmit Power Control
The current detector Q3040-1 (NJM12904V) detects
the current of Q3006 and Q3008, and converts the
current difference to the voltage difference.
The output from the current detector Q3040-1 is com-
pared with the reference voltage and amplified by
the power control amplifier Q3040-2.
The output from Q3040-2 controls the gate bias of
the final amplifiers Q3006 and the final amplifier
driver Q3008.
The reference voltage changes into four values
(Transmit Power High and Low) controlled by Q3040
(NJM12904V).
4. PLL Frequency Synthesizer
The frequency synthesizer consists of PLL IC, Q3036
(AK1541), VCO, TCXO (X3001).
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 Q3019
(2SK508) in VCO generates a programmed fre-
quency between 282.35 and 322.35 MHz (Version "I")
or 249.15 and 289.15 MHz (Version "K") as 1st local
signal.
While the radio is transmitting, the TX oscillator
Q3023 (2SC4227) in VCO generates a frequency be-
tween 350 and 390 MHz (Version "I") or 300 and 340
MHz (Version "K").
The output from oscillator is amplified by buffer
amplifier Q3017 (2SC5005) and becomes output of
VCO. The output from VCO is divided, one is am-
plified by Q3022 and feed back to the PLL IC 17 pin.
The other is amplified in Q3014 and in case of the
reception, it is put into the mixer as the 1st local sig-
nal through D3011, in transmission, it is buffered
Q3010, and more amplified in Q3008 and it is put
into the final amplifier Q3006.
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.
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