Motorola Saber Theory Maintenance 68p81044c05 O Manual

can be controlled by the coded/clear selector switch,
or by “strapping” on a per-channel basis using the
Radio Service Software. Regardless of the
coded/clear selector switch position or the channel
strapping, the radio will receive both coded and clear
transmissions.
4. PRINTED CIRCUIT BOARDS AND FLEXIBLE 
CIRCUITS
a. General
Functional circuits in the SABER radio are con-
tained on the main radio circuit board, and, in SABER
II and III radios, the display circuit board. Flexible cir-
cuits are used to...

3
BATTERY CHARGING
1. AVAILABLE CHARGERS
Available chargers include a single-unit desk top
charger, a single-unit Porta-Pocket charger, and multi-
unit chargers that may be mounted on a wall or a
bench. The multi-unit chargers will charge up to six
nickel-cadmium batteries at once.
The single-unit desktop and multi-unit chargers are
rapid-charge models, while the porta-pocket is a slow-
charge model. The slow-charge model will charge any
of the batteries, with or without the radio attached, in
16 hours....

a. Obtain a Radio Housing Adapter (Motorola part
number RTL-4225A) from your nearest Area Parts
Office.
b. Connect the appropriate 20-ohm or 11-ohm load
resistor (see note above) between the gold (+) ter-
minal and a solder lug (-) screw and nut of the
housing adapter.
c. Connect a voltmeter across the load resistor and
slide a fully charged battery onto the housing
adapter.
d. Monitor the voltmeter as the battery discharges
through the load resistor, until the voltage is 6.0
volts. 
e. Disconnect...

THEORY OF OPERATION
1. INTRODUCTION
This section of the manual provides a functional
description of the SABER radio. First, basic functions
are discussed, with each circuit and its relationship to
other parts of the radio described. Then, detailed cir-
cuit descriptions are given for each circuit and module
used in the radio.
2. BASIC FUNCTIONAL DESCRIPTION
a.  DC Voltage Distribution
(See Figure 2)
Operating power for the radio is derived from a
7.5-volt battery. This 7.5 volts (B+), is fed, via the...

sensing circuit of PA U202, and (uhf radios only) the
base of Q200.
RX 5V, identified by the Å symbol, is also provid-
ed by U201s 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 Æ
symbol. No.1B REGULATED 5V is distributed to
U200, pin 1, and U301, pin 4.
b.  Frequency Generation and 
Distribution Circuits...

er/prescaler (U300), and the signalling IC (U700).
The CORE uses its serial peripheral interface
(SPI) subsystem to program these ICs. The micro-
processor lines that make up the SPI subsystem
include the MISO (pin 28), MOSI (pin 29), and
SCK (pin 30) lines. In conjunction with the SPI, the
CORE uses dedicated output ports to select each
individual IC. Examples of when the ICs can be
programmed include channel changes, volume
changes, transitions from receive to transmit, and
transitions from transmit to...

also part of the audio filter IC (U101). The demod-
ulated, filtered, hard-limited signal is sent (U101,
pin 28) over the PL DECODE line to the CORE
processor (pin 41). At the instant that the CORE
wants to sample this line, it sends (pin 39) a latch-
ing pulse, via the PL SAMPLE/CLK line, back to
U101 (pin 33). This pulse latches the sample,
which can then be read by the CORE processor.
The frequency of the pulse is 1071 Hz for TPL or
537 Hz for DPL.
·
MDC Encode.The MDC encoder is part of the sig-...

c.  Digital-to-Analog (D/A) Converter (U200)
The digital-to-analog (D/A) converter, U200, is a
multifunction CMOS integrated circuit containing two
7-bit D/A converters, one 4-bit D/A converter, six con-
trol outputs, two SPDT transmission gates, and a
microcomputer interface.
The output (U200, pin 11) of the first 7-bit D/A con-
verter supplies the tuning voltage for the reference
oscillator, U301. When the R/T line is low (0V), the
output of the second 7-bit D/A converter is routed, via
an internal...

As in the vhf models, the TX/RX antenna switch-
ing is controlled by the R/T line (U201, pin 9). When
the R/T line is high (5V), the RX 5V regulator in U201
is on and supplying current to receiver U2. The supply
current for the RX 5V regulator is drawn from U203,
pin 10 (receive path PIN diode cathode). Current flow
through the receive path PIN diode causes a 
low-impedance rf path from U203, pin 9, to the select-
ed antenna. When the R/T line is high, the voltages 
at pin 26 of U201 and pin 7 of U203...

g. Receiving
The signal received at the antenna is routed
through the filter/detector/switch module (U203) and
applied to the receiver rf front end module for filtering,
amplification, and mixing down to the first i-f.
(1) RF and 1st I-F
(a) Mid-Band (U1, U4)
In the mid-band receiver string, rf enters U1, the rf
filter/amplifier module. This module consists of a dis-
crete-component, 3-pole bandpass filter, designed to
cover either the low (68-84 MHz) or the high (74-88
MHz) bandsplit, and a common-base,...