•
•
PRINCIPLES OF OPERATION
•
The
PRO-2004
is
aPhase Locked Loop (PLL) synthesized VHF/UHF, AM/FM Receiver controlled
bya
CentraIProcessing Unit (CPU) via
the
keyboard.
Receiving
mode
and
search step
are
initially
set
to correspond with
the
frequencies entered. When a fre·
quency within
FM
broedcast band
is
keyed in, receiving
mode
is
set
to
Wideband
FM
(WFM). When a
frequency in Action radio band, Police, Fire, Ambulance, Ham radio etc.
is
keyed in,
the
mode
is
set to
Narrowband
FM
(N
FM), and when a
frequency
in
Aircraft and
CB
band
is
keyed in,
it
sets
to
AM
mode.
Also
the
mode
and
step can be changed
by
!MODEl,
!STgP) Keys.
The CPU (IC·503)
controls
receiving
frequency
range, frequency determination, scanning speed, delay time,
etc. The CPU
is
able
to
do
only
the
assigned functions, and no modification
of
the
CPU
is feasible.
The following paragraphs explain
the
operation
of
the
circuit in
terms
of
the
functional bloeks:
RF
input
circuit cernprises 10 dB
attenuator
and
Bandpass filter. A signal generated
by
VCO-l
or
VCO·2
is
applied
to
Double balanced mixer (D.S.M.) via Low-pass or High-pass filter and mixed with
the
RF signaL
The
D.S.M. is
employed
to
facilitates
25
MHz
to
1300
MHz
mixing. --
The
1st
IF
(05)
is
607.505
MHz
to
611.500
MHz, and
the
signal is mixed with VCO-3 frequency
at
the
2nd
mixer
(06)
to
produce
48.5
MHz signal,
which
is
applied
to
WFM
IF
(012)
or
AM/NFM IF
(010,
018,
019).
Corresponding with
input
from
the
keyboard,
CPU
determines which
of
VCO-,
or
VCO·2,
WFM
IF,
AM/NFM,
AM
IF, Data
of
PLL
circuit
to
be functioned, and
outputs
the
necessary
data
.
. A signal
entered
to
AM/NFM IF
is
mixed
with
X'tal oscillation frequency 48.045
MHz
at
the
3rd mixer
(JC-2)
and
converted
to
.455 kHz signa!. A signaIentered
to
WFM
IF
is
mixed with X'tal oscillation frequen-
cy
37.8
MHz
at
the
3rd
mixer
(013)
and
converted
to 10.7
MHz
signal.
The
signals are further amplified
and
detected
to
AF
signa!.
•
•
AF signa
Is
of
WFM, AM,
NFM
are
CPU
controlled
and applied
to
AF
Power Amplifier (tC-7)
via
switching
circuit. Squelch signaI is comprised
of
noise
product
trom
WFM/NFM
detector
output,
and amplified by
IC·2
to
switching signal, which
centreis
AF
mute
and
CPU.
Any unstable
supp
ly voltage
te
the
CPU can produce
CPU
malfunetions, such as wrong data processing,
wrong
data
transfer,
etc~
Ta
overcome this
C512
and R501 "initialize"
the
CPU. Initialization
is
done when
RESTART switch is pushed. Figure A
shows
initiatizing waveform.
•
•
CX501 (7.37 MHz)
is
aclock which
is
used
for
CPU
control. Figure Bshows 1/4 divided waveform
at
Pin
.31
of
1C-503. •
••
CPU
output
data
display frequency,
function,
etc. on LCD.
LCD
is
back lighted with Electra Luminescence,
which works from
70
V rms,
300
Hz
A.C.
Power
supply
comprises D.C
30
V,
8 V and
two
5Vlines.
I
•
•
11:503
28
(lSOI
CSl2
s
·v--
- - - -
-~-:;-::;-;::.:::-.=-:.-
_
0.4
•
IC503
31
tt
1IO
R:lOZ
r-
--
---,
I
1.
Dr-
I
: T T
:C~1
I I
'----
---~
5V-----~
•
•
0\1--
Figure A
ov-----
i.o
.:I<"
IFigure B
