Theory Of Operation (Basic Functional Description); Introduction; Radio Power; General - Motorola HT 1000 series Theory/Troubleshooting Manual

THEORY OF OPERATION (BASIC FUNCTIONAL DESCRIPTION)

I.

INTRODUCTION

This publication covers a large family of portable
radios: HT 1000, MT 2000, MTS 2000, and MTX series
units. They are software driven, and because of the
wide range of operating systems and radio functionality
provided by this family of radios, the theory discussions
will be divided into several major categories. The
transceiver is frequency sensitive and falls into one of
four frequency bands: vhf, uhf, 800MHz, or 900MHz.
Because of their similarity, transceivers will be catego-
rized into two discussion groups: vhf/uhf transceivers
and 800/900MHz transceivers. The controller falls into
two categories: a closed architecture controller and an
open architecture controller. Each controller will be dis-
cussed separately. This THEORY OF OPERATION
section of the manual provides a functional description
of the radio. First, overall radio functions are discussed
in basic terms, with each circuit and its relationship to
other parts of the radio described. Then, a more detailed
functional description is given for circuit relationships,
with special attention directed to some of the selected
circuits. Pay particular attention to the topics being dis-
cussed, and note the application: vhf/uhf transceiver,
open architecture controller, etc.
II. RADIO POWER
A. General
In this family of radios, power is distributed to four
general combinations of transmitters and controllers:
1. vhf/uhf xcvr with closed architecture controller
2. vhf/uhf xcvr with open architecture controller
3. 800/900MHz xcvr with closed architecture controller
4. 800/900MHz xcvr with open architecture controller
Discussing each of the four combinations would be
somewhat redundant, so pairs 1 and 4 were chosen for
illustration and explanation in the following paragraphs.
Paragraph B covers the vhf/uhf transceiver and the
closed architecture controller; paragraph C covers the
800/900MHz transceiver and the open architecture con-
troller.
B. B+ Routing and DC Voltage Distribution
(for a Closed Architecture Controller and a

VHF or UHF Transceiver)

Operating power for the radio is derived from a 7.5-
volt battery (BATT 7.5V), which is applied directly to the
transceiver board as B+. The B+ voltage is fused and
routed through the jumper flex as Raw B+ and applied
through the controller board to the controls flex. In the
controls flex, B+ is applied to the on/off/volume control.
When the radio is turned on, switched B+ (SB+) and the
2
voltage sources required to operate various stages of
the radio are distributed as shown in Figure1A.
The power amplifier (PA) module (U105) and auto-
matic level control (ALC) IC (U101) of the RF board are
powered-up directly from the BATT B+. Other sections
of the transceiver board are powered-up through the
switched B+. Two 5-volt regulators are used on the
transceiver board; one 5V regulator (U202) is used to
supply those circuits which require voltages to be on all
the time, such as the reference oscillator, synthesizer
IC, IF IC, and digital-to-analog (D/A) IC. The voltage-
control oscillator (VCO) buffer obtains its voltage (Vcc)
from the SOUT line of the synthesizer. The other 5V
regulator (U103) of the transceiver board supplies 5V to
the receiver RF AMP IC and Mixer IC during the receive
mode and to the ALC and other transmitter circuitry dur-
ing the transmit mode.
The controller board obtains its voltage source from
switched B+, and produces regulated 5 volts from two
regulators. One 5V regulator (U709) is used to supply
5V to the microcomputer. The SB+ is also connected to
the AUDIO PA. The audio signalling filter (ASF) IC
obtains its 5V (Vcc) from the AUDIO PA (U706) internal
5V regulator.
C. B+ Routing and DC Voltage Distribution
(for an Open Architecture Controller and an

800 or 900MHz Transceiver)

Refer to figure 1B and note that operating power for
the radio is derived from a 7.5-volt battery (BATT 7.5V),
which is applied directly to the transceiver board as B+.
The B+ voltage is fused and routed through the jumper
flex as Raw B+ and applied to the controller board.
From the controller, B+ is applied to three different
areas:
1. the expansion board, via connector jack J702 pin1,
2. an electrical switch IC, U712 pins 2 and 3, and
3. the controls flex, via connector jack J703 pin 8.
The UNSW B+ is routed to the expansion board so
that functions there can be performed independently of
the SW B+ supply. The UNSW B+ is also routed to the
electrical switch IC, U712 (a P-channel FET in an SOIC-
8 package), which connects it to SW B+ when the
control voltage at U712 pin 4 is low. The SW B+ is then
distributed to the rest of the radio, including the
transceiver board, front cover/display flex, and expan-
sion board, as well as other controller board circuitry.
Finally, UNSW B+ is routed to the mechanical on/off
switch and returns to the controller as MECH SWB+.
The MECH SWB+ signal activates the electrical switch
(U712), and also feeds a resistive divider so that the
microprocessor (U705) can monitor the battery voltage.