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PRINCIPLES OF OPERATION
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The PRO-2004 is a Phase Locked Loop (PLL) synthesized VHF/UHF, AM/FM Receiver controlled bya
Centra I Processing 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.
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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.
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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 signaI entered 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!.
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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
supply
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.
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CX501 (7.37 MHz) is a clock which is used for CPU
control.
Figure B shows 1/4 divided waveform at Pin
.31 of 1C-503.
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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 5 Vlines.
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11:503
28
(lSOI
CSl2
s·v--
- - - -
-~-:;-::;-;::.:::-.=-:.-
_
0.4
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IC503
31
tt
1IO
R:lOZ
r- --
- - - ,
I
1. Dr-
I
: T
T
:C~1
I
I
'----
---~
5V-----~
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0\1--
Figure A
ov-----
i.o.:I<"
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Figure B
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