VXR-5000
RPP
Programming Software Instruction
RX
Unit
VCO Q5502 (2SK302GR) oscil-
lates
between
112.4
and
152.4
MHz
according
to
the
programmed
receiving frequency
and
repeater version type. A sample of the VCO
output
is amplified
by
Q40l5 (2SC3356)
and
returned to
the
prescaler / swallow counter in
Q40l4. There
the
VCO signal is divided
by
64
or
65,
according to a control signal from the
data latch section of
Q1009
on
CNTL Unit
1,
before being applied to the programmable
divider section of the
PLL chip.
The
data
latch section of Q4014 also re-
ceives serial dividing
data
from microproces-
sor
Q1009
on
CNTL
Unit
1, which causes the
pre-divided
VCO signal to
be
further divided
by
11,240
- 15,240
in
the
programmable. di-
vider section,
depending
upon
the desIred
receive frequency, so as to produce a
10-kHz
or
12.5
kHz
derivative of
the
current VCO
frequency. Meanwhile,
the
reference divider
section of
Q4014 divides the 12.8 MHz crystal
reference
by
1280 (or 1024) to produce the
10-kHz (or 12.5-kHz) loop reference.
The
10-kHz
or
12.5
kHz
signal from the
programmable
divider
(derived
from the
VCO),
and
that derived from the crystal are
applied
to
the
phase
detector
section of
Q4014,
which
produces
a
dual
phase-de-
tected
9-VDC
pulsed
output
with
pulse dura-
tion
depending
on
the
phase
difference
between
the
input
signals. This pulse train is
then converted to DC, low-pass filtered, then
fed back to varactor diodes
D5501, D5502,
05503
& D5504 in the
RX
VCO Unit.
Changes in the DC voltage applied
.to
the
varactor diodes affect the reactance
In
the
tank circuit
VCO Q5507, changing the oscil-
lating frequency according to the phase dif-
ference
between
the
signals derived from the
VCO
and
the crystal reference oscillator. The
VCO is
thus
phase-locked to the reference
frequency standard. The
output
of
RX
VCO
Q5507,
after buffering
by
Q5501, is delivered
for
amplification
to Q4012 (2SC3356) &
Q4011
(2SC3357) before application to the
first mixer, as described previously.
2-2
Transmitter
Transmitter VCO Q5002 (2SK302GR) os-
cillates between 134 -174
MHz
according to
the programmed
TX
frequency
and
repeater
version type. The theory
of
operation
of
the
remainder of the
PLL circuitry is similar to
that of the
RX
VCO Unit, however,
dividing
data from the microprocessor is
such
that
the
VCO frequency is
the
actual
transmit
fre-
quency.
IDC-processed speech
audio
from CNTL
Unit 2 is pre-emphasized
by
C20l0, R2006
and
Q2002-4(uPC4747) before application to
the
TX
VCO.
To
prevent
over-deviation, the
audio is processed
by
IDC (instantaneous de-
viation control) circuitry
on
CNTL
Unit
2 be-
fore delivery to
the
TX
Unit. Speech
audio
is
delivered to diode
D5006 (1T363) from Con-
trol
Unit 2, frequency
modulating
the
PLL
carrier
up
to ± 5
kHz
from the
unmodulated
carrier
at
the transmitting frequency.
DCS modulation from control
Unit
2 is low
pass filtered
by
Q3002 (NJM2904M),
then
ap-
plied to both the
VCO
and
to
the
PLL fre-
quency reference,
via
reference frequency
standard
X3001(GFS-720). The
modulated
signal from
TX
VCO
unit
is
buffered
by
Q5001 (2SC3356)
and
Q3011 (2SK1577),
then
passes
through
buffer-amp
Q3010
(2SC3356). The signal
then
passes
through
RF
diode switch D3003 (HSU277)
and
ampli-
fier
Q3009 (2SC3356). The signal level is
then
attenuated before delivery to
the
PA
Unit.
The signal first passes
through
the
low-pass
filter formed
by
inductor
L6001
and
capaCItor
C6003
and then buffer
amp
Q6001 (2SC2954)
before being applied to pre-driver amplifier
Q6002 (2SC2954).
The transmit signal is
then
finally ampli-
fied
by
PA
module
Q6003 (M67741
[[H]
in
C-
versions, M67741 [L]-in
A&B
Versions)
up
to
25
watts. Harmonic
and
spurious
radiation in
the final
output
is suppressed
by
as-pole
low-pass filter formed
by
inductors L6008,
L6009
and
L6010
and
capacitors
C6016,
C6017, C6018. C60l9
and
C6020
on
the
PA
Unit before delivery to the
TX
antenna
jack.
If
a
CTCSS
tone is enabled for transmission, the
sub-audible tone from the
unit
is low-pass
filtered, then mixed
with
the IDC-processed
speech audio.
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