l.
PRINCIPLES OF OPERATION
The PRO-2027 is a PLL (Phasa Locked Loop) syntheslzed VHFtIJHF, FM/AM race!ver, controlled by a CPU (Central
Processing Unit) via a keyboard.
•.
The VHF La band (30-54 MHz) or VHF Hl band (137-174 MHz) is raceived in 5 kHz lncrërnente and ths UHF La
band (380-512 MHz) or UHF Hl band (808--960 MHz) is set up
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ee in 12.5 kHz inc'ements. Similarly, the alrcratt
band (108-136,975 MHz) ia in 25 kHz steps.
All funGlions, such as the receiving trecuency ranga, frequency determination, and scanning and delay time. are
çonlrolled by the CPU. The CPU is able 10do only the assigned fum:lions and no modificatlon ot th.. CPU is teaslble.
Tha followlng paragraphs explatn the operation of the circuit in terrne of the functional bloeks:
Varactor (vanable capacrt
...
nce diode) tuning ("automatic luning syslem") is employed on all bands.
Field-effect transistors (FET) are used inthe RFIMIX circuits of low and high bands to eenleve optimum mix-modulatlon
ano mutual-modulatlon characteristlcs. Q23 amplifies Ihe 10.7 MHz IF. A 10.7 MHz monolithic ervetal tilier is
incorporated to oblain
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good
lf
selE>ctivity.
IC2 contains Ihe locai oscillator, mixer, IF amplifier. quadralure FM detector, and noise ampmier. A crystel oscutator
produces 10.245 MHz which is mixed wrth 10.7 MHz, resuiling in 455 kHz IF. A 455 kHz ceramic filter i8 provided
la lncrease the IF selectlvlty. The 455 kHz IF signal is ampiified in tha IF amp stage. and Ihe quadreture FM oetector
deteets it as an audio signal.
The detected output of Ihe FM is applied
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iC7. IC7 amplifies the audio slqnals and drives Ihe speaker.
IC6 is Ihe
cpu.
which does data processing and calculation. Any unstebla supply voltage (VDD) to tha CPU een
eause CPU maltunetlens. such as wrong data processing and wrong data transfer. To overcome Ihis,
C17l
and
R150 in the logle circuil "Initialize" Ihe CPU. (Refer
10
Ihe schemalic diagram on Page 55)
The inltlalizalion is done as soon as power is connected. Figure A
shcw"
the initielizlng waveform. The memory
backup
tunencri
is aulomatlcaily siaried whenever the initiallzation has been ccne.
t-j
The RESET switch is
IOCllted
In the hole on tho back of the unit end is used
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correct an LCD or keyboard
maifunction. Initiel;zallon of Ihe CPU, as mentioned ecove, can
...
Iso be
don"
by pushing RESET.
Key input and recalvlng trequ"ncy are managed by thc CPU, and Ihe CPU outpul drives the LCD.
CX1 (8 MHz) is a ceramic osoillator which is used
lor
CPU control. Figure B shows 1/8 divtded of Ihe waveterm of
Figure C.
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