RPP
Programming Software Instruction
VXR-5000
Circuit Description
Receive Signal Path
~com.ing
RF
from
the
RX
antenna jack is
dehvered
to
the
RX
Unit
and
passes
through
the
bandpass
filter consisting of coils L4002,
L4003
and
L4005, capacitors C40l6, C4017,
C4019, C4021
& C4023. Signals within the
frequency
range
of
the
receiver are then am-
plified
by
Q4010(3SK131). The amplified
RF
IS
then
bandpass
filtered
again
by
L4011,
L4013, L4015,
and
C4046, C4050, C4054,
C4057, C4061
and
C4067 to ensure
pure
in-
band
inP1:lt
to
the
first double-balanced mixer
D4003 (DBM0135).
Buffered
output
from
the
VCO Unit is am-
plified
by
Q4011 (2SC3357)
and
low-pass fil-
tered
by
L40l4, L4016, C4056, C4060, C4062
and
C4066, to
provide
a
pure
first local signal
between 112.4
MHz
and
152.4 MHz to the
first double-balanced mixer. The 21.6 MHz
first mixer
product
is amplified
by
Q40l8
(2SC3356),
then
passed
through
dual
mono-
lithic crystal filter
(± 7.5
kHz
BW)
XF-4001
(21P15BU-1), to strip
away
all
but
the de-
sired
signal,
which
is
then
amplified
by
Q4024 (2SC3356).
The amplified 1st IF signal is then applied
to
~
IF subsystem IC Q4017 (MC3372ML),
which contains
the
2nd
mixer, 2nd local oscil-
lator
and
limiter amplifier. A
2nd
L.a.
signal
generated
from
the
22.055
MHz
crystal
X4003,
produces
the 455
kHz
2nd
IF
when
mixed
with
the
1st
IF
within
Q4017. The 2nd
IF
then passes
through
ceramic filter CF4001
(CFW455E), to strip
away
any
unwanted
mixer products,
and
is
then
applied to the
limiter
amp
in
Q4017,
which
removes any
amplitude
variations
in
the
455
kHz
IF
before
detection of speech
by
ceramic discriminator
CD4001 (CDB455C16). The detected audio is
amplified
by
Q40l6 (NJM2902M)
and
deliv-
ered to
J4002-pin-1 (DISC OUT).
Squelch Control
When
no
carrier is received, noise at the
output
of the detector stage from Q40l7,
pin
9 is
sampled
and
fed to squelch gate Q4021
(2SA1179), VR-4001
adjusts
the
squelch
threshold before delivery to
the
3-pole active
bandpass
filter formed
by
Q4025
and
Q4026
Instruction
Manual
(both 2SC2812),
where
the
audio
is de-em-
phasized
and
audio
frequencies above 5-kHz
are rejected. The noise signal is
next
amplified
by
Q4023
and
Q4020 (both 2SC2812),
then
rectified
by
diode
D4004(1
SS226)
to
produce
a DC control voltage for
the
squelch switch
section
in
Q4022. This resulting DC voltage is
amplified
by
Q4016-4(NJM2902M),
then
compared
with
a reference voltage
of
9 VDC
at
Q40l6-3. The open-collector
output
volt-
age from analog switch
Q4022 (DTC144EK)
is delivered to
J4001
pin
7 (NSQ DET)
and
on
to microprocessor Q1009
pin
26 (NSQ DET).
Then, microprocessor
pin
14 (U N E OUT)
goes
high,
turning
on
analog
mute
gate
Q2001 (NJU4066DM)
on
Control
Unit
2, al-
lowing
audio
to
pass
from J2007,
pin
1 (DISC
IN) through
audio
stages Q2008
and
Q2006 to
line selector
Q2004 (uPD4052BG).
CTCSS Operation
A
CTCSS
(Continuous
Tone-Coded
Squelch System) is
provided
by
program-
ming
via
CE-8
Software.
The
CTCSS IC
Q2008 (MX165CLH) contains a CTCSS tone
encoder for
anyone
of
39
subaudible
tones.
The
CTCSS
audio
level
output
from
pin
16
of
Q2008 is amplified
by
Q2005-1(NJM2902M),
and
adjusted
by
VR2003 before injection into
the
audio
chain
at
Q2003-2 (NJM2902M).
S-Meter
S-meter signal is
output
from
pin
13
of
Q4017(MC3372ML) to C4118
where
the 455
kHz
signal is rejected(filtered), to buffer am-
plifier
Q4016-2(NJM2902M)
through
J4001
pin
1 to CNTL Unit-I.
RX
PLL & VCO Circuit
PLL circuitry
on
the
RX
unit
consists of
PLL
subsystem
IC Q4014(MC1415190F),
which contains a reference oscillator / divider,
serial to parallel
data
latch,
programmable
divider,
phase
comparator
and
a swallow
counter.
Stability is
obtained
by
a regulated
5-VDC
supply
via
Q4001 (TA78L05) to Q4009
(DTA143EK)
and
temperature
compensating
capacitors associated
with
the
12.8
MHz
fre-
quency
standard
X4002 (GFS-720).
2-1
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