PRINCIPLES OF OPERATION
The PRO-2022 is a Phase Locked Loop (PLL) synthesized VHF/UHF, FM receiver,controlled
by
aCentral Pro-
cessing Unit (CPU) via a keyboard.
The VHF Lo band (30 - 54 MHz)
or
VHF Hi band (136.005 - 174 MHz) is received in 5 kHz increments, and the
UHF Lo band (380 -512 MHz)
or
UHF Hi band (806 - 960 MHz) is set up
to
be 12.5 kHz increments.Similarly, the
aircraft band (108 -136 MHz) is in a 25kHz step.
All functions such as receiving frequency range,frequency determination,scanning and delay time,etc., are con-
trolled
by
the CPU. 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 blocks:
AvariabIe capacitance
diode
(varactor) tuning ("Automatic Tuning System
")
is employed
on
all Bands.
Field-effect transistors (FET) are used in the RF/MIX circuits
of
10
and hi bands,
to
achieve optimum mlx-rnodula-
tion and mutual-modulation characteristics. Q18 amplifies the 10.7
MHz
IF. A10.7MHz monolithic crystal filter
is
incorporated
to
obtain a
good
IF selectivity.
IC1
contains the local oscillator, mixer,
IF
amplifier, quadrature
FM
detector, noise amplifier. Acrystal oscillator
produces
10
.245 MHz.which is mixed with 10
.7
MHz.resulting in 455 kHz IF. A 455 kHz ceramic filter is providec
to
increase the IF selectivity. The 455 kHz IF signal is
amp
lified in the IF
amp
stage,and the quadrature FM detec-
tor
detects it
to
an audio signa
!.
The detected output of FM is applied
to
IC3. IC3 amplifies the audio signals and drives the speaker.
IC7 is the CPU. The CPU does data processing, calculation etc.Any unstable supply voltage
(V
DD)
to
the
CPU
can
cause the CPU
to
malfunction,such as wrong data processing,
wrong
data transfer etc.
To
overcome this, C164
and R167 in the
logic
circuit "initializ
e"
the CPU. (Refer
to
the schematic on page 55
.)
The initialization is
done
as soon as AC plug
or
external power is connected. Figure Ashows the initializing wave-
form.Memory back
up
function is automatically started whenever the initialization has been done.
The RESET switch is located in the hole on the read panel and is used
to
correct an LCD
or
keyboard maltune-
tion. The initialization of the CPU, mentioned above can also be
done
by
pushing RESET.
Key inpu
t,
receiving frequency,etc. is managed
by
the CPU, and CPU output drives LCD.
CX1
(2
MHz) is a ceramic oscillator clock which is used for CPU control. Figure Bshows 1/8 divided waveform of
Figure C.
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