Table of Contents
Advertisement
RX
5V, identified by the
"©"
symbol, is also provid-
ed by U201's
internal
TX/RX
5V
regulator.
This voltage
is distributed
to
the following circuits: pin 22 of U201;
pin
7 of
U1
and pin 2 of T1 (vhf) or
pin
3 of U2 (uhf).
No.1B
REGULATED
5V
(vhf radios only) origi-
nates at U100,
pin 14,
and is identified by the
"@"
symbol. No.1B
REGULATED SV
is
distributed
to
U200,
pin 1,
and
U301,
pin
4.
b.
Frequency Generation and
Distribution
Circuits
(U300, U301)
The
SABER
radio
uses a
coherent synthesizer
(traditional voltage-controlled
oscillators
[VCO]
and
phase-locked
loop
[PLL])
with
state-of-the-art
designs
to
generate frequencies that support a dual-conver-
sion radio
with unlimited
capabilities
in
the mid-band,
uhf, and
vhf ranges
with operating
splits of up to 30
MHz.
The
rf
frequency generation circuits include the
reference oscillator, U301, and the synthesizer, U300.
The synthesizer
has three major subassemblies: oscil-
lator, controller
(PLL/divider),
and buffer/amplifier. To
provide superior system performance, each sub-
assembly is
broken down
into
a separate
TX
and
RX
section.
The
synthesizer (U300,
pin 1)
uses
the 16.8
MHz signal
from
the reference oscillator
(U301,
pin
3)
in
conjunction
with its own internal
dividers and
VCOs
to
generate
and
synthesize
the following frequencies:
e
TX
carrier (U300,
pin
14),
e
local oscillator (1st injection) (U300,
pin
15),
e
2nd
local oscillator (both high- and low-side
injection) (U300,
pin
32),
e
2.1
MHz (U300,
pin
17), and
e
300
kHz
(internal only).
The
audio
in
the
SABER
synthesizer is simultane-
ously
modulated at two different ports.
The
audio is
first conditioned
(pre-emphasis and
limiting)
externally
by audio filter U101, then sent,
via
the
VCO
MOD and
REF
MOD lines,
to two different ports on the
synthe-
sizer
module, U300.
The
reference modulation
port
(U300,
pin 19)
accepts
low-frequency audio
(<70Hz)
and modulation
is produced by
varying the frequency
of the
synthesiz-
er
in
proportion to the audio input
voltage.
The
VCO
modulation port
(U300,
pin
3) accepts
high-frequency audio
(>70Hz)
and modulation is pro-
duced by varying the control voltage
of the
VCO
in
proportion to the high
frequency audio
input.
The
dual-
modulation scheme allows for a flat deviation
response
for all
desirable signals
that readily support
Motorola's
PL
channels
and
sensitive
SECURENET
radios.
The
following
generic
(TX
or
RX)
description of the
SABER
synthesizer
is used
because
of the symmetri-
cal hardware
and operational
systems
for both the
TX
and
RX
sections.
The
VCO
becomes active and gen-
erates an
output frequency, which is
compared
to the
desired frequency.
If
the frequencies differ, an error
ramp
voltage
is
generated
to the
VCO
that brings the
output
frequency
to
the desired frequency.
When the
output and
desired frequencies match, the
VCO
is
locked.
The
locked state
of the
synthesizer can
be
observed externally by looking
for
zero volts
on the
LOCK
DETECT
line of the
synthesizer (U300,
pin
16).
c. Antenna Switch and Bias Circuits
Steering
of
rf
between receiver and transmitter,
and standard and remote antennas, is accomplished
electronically by
a
4-port PIN diode switch located
in
the filter/detector/switch module, U203.
This
module
also contains a directional coupler and power detector
that supply the
system
with an indication of
transmit
output power.
Low-pass
filters are
also included
to
attenuate transmitter and receiver (mid-band only)
harmonics.
d.
Display Circuitry
(SABER
Il
and
Ill
radios only)
The display circuitry
for the
SABER
II
and
III
radios includes the liquid-crystal.display
(LCD)
and the
display circuit board. This
board, mounted
on
the
radio's front shield, provides
SABER
II
and
III
radios
with additional and
expanded capabilities. Two basic
types
of
display boards are available: the standard 8k
board, and the optional 2k board (not
available
on
mid-band models). Both boards have four
ICs
in
common:
e
An MC68HC11 microprocessor, U502. This IC is
also called
the
COPE
(control
of
peripheral
electronics).
e
An electrically-erasable, programmable read-only
memory
(EEPROM),
U501.
This IC's
memory
size
is either two kilobytes
(2k
board) or eight kilobytes
(8k
board).
e
A
liquid-crystal display
(LCD)
driver,
U504.
e
Aserial-to-parallel
shift register, U503.
The 8k
board
has one
additional IC, the dual-tone,
multi-frequency
(DTMF)
generator, U505.
The display
board communicates with the radio
board
via
the 8-wire
LCD
interconnect flexible
cable
(J8);
this
cable provides
both
power and signal paths.
There
is also
(8k
board only)
a
3-wire connection
to
the speaker/microphone flex
(J9)
that is used
as a
DTMF
signal
path.
e.
SECURENET
Circultry
(SECURENET
radios only)
The
SECURENET
module
(U900)
requires an
encryption key,
or
key variable,
to
perform its
encode/decode function. This key
is a digital
sequence
that is loaded
into the radio,
via
the radio's
universal connector,
from
a
hand-held key variable
loader (such
as
the
T3010BX DVP
Keyloader, which is
suitable for all radios
with the
DVP
algorithm).
In
order
for two
SECURENET
radios
to
communicate
with
each
other
in
the
secure
mode, both must
have the
same
encryption
key loaded.
6
Advertisement
Table of Contents
