Vertex Standard VX-6000V, Руководство по обслуживанию

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4-1
Circuit Description
Transceiver functions, such as PLL synthesizer
settings and channel programming, are controlled
via the microprocessor unit (MPU). Reception and
transmission are switched by "RX" and "TX" lines,
also controlled from the MPU.
Main Receiver Signal Path
The receiver uses double-conversion superhet-
erodyne circuitry, with a 43.95 MHz 1st IF and 450
kHz 2nd IF. The 1st LO, produced by a PLL synthe-
sizer, yields the 43.95 MHz 1st IF. The 2nd LO uses
a 43.5 MHz (43.95 MHz - 450 kHz) signal generated
by a crystal oscillator. The 2nd mixer and other cir-
cuits use a custom IC to convert and amplify the 2nd
IF, and detect FM to obtain demodulated signals.
Incoming RF signals from the antenna connector
are delivered to the PA Unit, and pass through a
low-pass filter (LPF) network consisting of coils
L6009, L6008, and L6007, capacitors C6041, C6047,
C6040, C6050, C6039, and C6027, and the antenna
switching relay for delivery to the receiver front end
in the Main Unit.
Signals within the frequency range of the trans-
ceiver are then passed through a varactor-tuned
band-pass filter consisting of L1007 and L1020 be-
fore RF amplification by Q1018 (
2SC3356
).
The amplified RF is then band-pass filtered again
by varactor-tuned resonators L1009 and L1011 be-
fore and then to ensure pure in-band input to 1st
mixer consisting of trances T1001, FET Q1043
(
SPM5001
).
Buffered output from the VCO Unit is amplified
by Q1032 (
2SC4227
) and low-pass filtered by L1041,
L1045 and C1153, C1154 and C1174 to provide a pure
1st local signal between 191.95 and 217.95 MHz for
input to the 1st mixer.
The 43.95 MHz first mixer product then passes
through second RF amplification by Q1030
(
2SC3356
) and dual monolithic crystal filters XF1001
and XF1002 (7.5 kHz BW) for wide band or XF1003
and XF1004 (3.75 kHz BW) for narrow band, and is
amplified by Q1041 (
2SC4226
) and delivered to the
input of the FM IF subsystem IC, Q1034
(
TA31136FN
). This IC contains the 2nd mixer, 2nd
local oscillator, limiter amplifier, FM detector, noise
amplifier, and squelch gate.
The 2nd LO in the IF-IC is produced from TCXO
X1001 (14.500 MHz), and the 1st IF is converted to
450 kHz by the 2nd mixer and stripped of unwant-
ed components by ceramic filter CF1001 or CF1002.
After passing through a limiter amplifier, the signal
is demodulated by the FM detector.
Demodulated receive audio from the IF-IC is
amplified by Q1036 (
2 S A 1 6 0 2 A
), Q2019
(
CXA1846N
). After volume adjustment by the AF
power amplifier Q2018 (
TDA7240AV
), the audio sig-
nal is passed to the speaker jack or the internal 4-
Ohm loudspeaker.
PLL Synthesizer
The 1st LO maintains stability from the PLL syn-
thesizer by using a 14.500 MHz reference signal from
TCXO X1001. PLL synthesizer IC Q1033
(
SA7025DK
) consists of a prescaler, reference
counter, swallow counter, programmable counter,
a serial data input port to set these counters based
on the external data, a phase comparator, and charge
pump. The PLL-IC divides the 14.500 MHz refer-
ence signal by 725 using the reference counter (20.0
kHz comparison frequency). The phase detector
comparison frequency is designed to be eight times
the channel spacing (2.5 kHz). The VCO output is
divided by the prescaler, swallow counter, and pro-
grammable counter. These two signals are compared
by the phase comparator and sent to the charge
pump. A voltage proportional to their phase differ-
ence is delivered to the low-pass filter circuit, then
fed back to the VCO as a voltage with phase error,
controlling and stabilizing the oscillating frequen-
cy. This synthesizer also operates as a modulator
during transmit.
The RX-VCO is composed of Q1019 (
2SK520
) and
D1010, D1011, D1016, D1018 (
HVU306A
X4), and os-
cillates between 191.95 MHz and 217.95 MHz accord-
ing to the programmed receiving frequency. And
the TX-VCO is composed of Q1020 (
2SC5107
) and
D1014 and D1015 (
HVU306A
X2), and oscillates be-
tween 148.0 MHz and 174.0 MHz according to the
programmed transmit frequency. The VCO output
passes through buffer amplifier Q1026 (
2SC5107
),
and a portion is fed to the buffer amplifier Q1029
(
2SC5107
) of the PLL IC, and at the same time am-
plified by Q1032 (
2SC4227
) to obtain stable output.
The VCO DC supply is regulated by Q1006
(
2SC4154E
). Synthesizer output is fed to the 1st mix-
er by diode switch D1025 (
1SS321
) during receive,
and to drive amplifier Q1031 (
2SC5415E
) and Q1025
(
2SC2954
) for transmit. The reference oscillator
feeds the PLL synthesizer, and is composed of TCXO
X1001 (14.500 MHz).