Motorola R-20010 Maintenance Manual page 504

SECTION 23.
ENHANCED TRUNKED RADIO TEST OPTION
23.1 DESCRIPTION
Motorola trunked radios can be tested using the
Trunking Test board. By selecting tests from a menu
on the screen, the operator uses the board to provide
data and generate the necessary signal to communi-
cate with a Motorola trunked radio. This board is also
used to auto test trunked radios over the entire fre-
quency range.
23.2 THEORY OF OPERATION
23.2.1 TRANSMITTED DATA
The system microprocessor generates all data trans-
mitted to the Motorola trunked radio under test. A
serial communication controller (SCC) (U10) gener-
ates both control channel and voice channel transmit-
ted data. The control channel data is modulated onto
the control channel by the trunking synthesizer (U25
and U27). The voice channel data is added to the EXT
MOD of the R2001D synthesizer using U30 and U22A.
The transmit clock is divided down from the 3.6864
MHz oscillator (U7) to the desired data rates using the
SCC. Control Channel data is transmitted out at TP3
at 3600 bits per second (bps) by the SCC. High speed
handshaking is transmitted out at TP4 at a data rate
of 3600 bps. Low speed handshaking is transmitted out
at TP4 at 150 bps.
The microprocessor counts the number of control
channel bits transmitted to allow synchronization to
the receive data stream. Ull is used to gate and clock
a timer (U13) in order for the microprocessor to read
the number of bits transmitted.
23.2.2 RECEIVED DATA
The data received from the trunking radio is shaped
to TTL levels using a center slice circuit (U18 and
U19). The SCC samples the data at four times the
receive data rate (14.4 kHz). The SCC data is then read
by the microprocessor to determine the received data.
The receive clock is divided down from the 3.6864
MHz oscillator (U7) to 14.4 kHz by U8.
23.2.3 DATA DETECT CIRCUIT
The data detect circuit operates as a fast attack
squelch circuit. Since t he squelch is always open in
trunking modes, noise is present in the DEMOD CAL
AUDIO input unless the radio is transmitting. The
received signal is amplified by U31A and high pass fil-
tered (U21A). The output of U21A is then integrated
by U21B and compared with a known level to indicate
whether noise or a signal is present. The output of
U19B will be a logic 0 if signal is present.
23.2.4 MODULATION
The audio modulation paths are enabled or dis-
abled depending on whether or not a trunking test is
in progress. If no trunking test is in progress, the EXT
MOD RTN (0), INT MOD RTN (0), and the 1 kHz
SINE RTN (0) paths are enabled. At t he beginning of
a trunking test and until the radio is on the voice
channel, the EXT MOD RTN (1), INT MOD RTN (0)
and the 1 kHz SINE RTN (0) paths are disabled. The
EXT MOD RTN (0) path continues to be enabled as
the high speed/low speed data is transmitted through
U30. After the radio has completed t he signalling
required for the test, EXT MOD RTN (1), INT MOD
RTN (0), 1 kHz SINE RTN
(O)
paths are enabled.
The 1 kHz SINE RTN (0) line can be used to meas-
ure receiver distortion and sensitivity. EXT MOD
INPUT can be used to add an external modulation
source.
23.2.5 RF SECTION
23.2.5.1 General
The trunking RF section provides a modulated con-
trol channel for transmitting data to Motorola trunked
radios. The design uses a frequency synthesizer, a
crystal oscillator, and an output mixer to generate this
control channel over three different trunking bands:
851.0000 to 866.0000 MHz in 12.5 kHz steps; 850 to
859.9750 MHz in 6.25 kHz steps, and 935.000 to
940.9875 MHz in 12.5 kHz steps.
23.2.5.2 Frequency Synthesizer
The frequency synthesizer is a single loop design
with a VCO (U25) capable of operating over two fre-
quency bands. The lower band ranges from 401 MHz
to 412.5 MHz, while the upper band covers from 423.5
MHz to 435 MHz. The digital synthesizer (U28) uses
a 6.25 kHz reference derived from a 12.8 MHz oscilla-
tor (U27). The frequency of this oscillator can be
adjusted via a digitally-controlled attenuator (U45, 46)
connected to the warp voltage input. The synthesizer
provides direct FM modulation from 1 Hz to 3.6 kHz
using dual port modulation techniques. The deviation