LBI-39006
MAINTENANCE MANUAL
CHANNEL GUARD ENCODER/DECODER
OPTION MHCG1E (349A9730P27)
FOR
MONOGRAM SERIES PORTABLE RADIO
30-50 MHZ
TABLE OF CONTENTS
Page
SPECIFICATIONS ..............................................................................................................................................................1
DESCRIPTION......................................................................................................................................................................1
PINOUT/FUNCTIONS............................................................................................................................................2
INSTALLATION.....................................................................................................................................................2
ALIGNMENT ........................................................................................................................................................................3
NOISE SQUELCH THRESHOLD, 10 DB SINAD.................................................................................................3
TONE DEVIATION ADJUSTMENT.....................................................................................................................3
SCHEMATIC & OUTLINE DIAGRAM
Channel Guard Board...............................................................................................................................................4
PARTS LIST ........................................................................................................................................................................4
SPECIFICATIONS
Tone Frequencies 37 (Standard EIA)
67 to 250.3 Hz
Modulation Limits 500 - 1000 Hz
Decode Sensitivity 8 dB SINAD
Receive Response Time 250 ms max.
Encode Response Time 75 ms max.
Transmit Tone Distortion 5% max.
Transmit Intermodulation Distortion 15% max.
Power 5 Vdc, 4.5 mA
Temperature Range -30° to +60°C
ericssonz
LBI-39006
DESCRIPTION
Channel Guard Option MHCG1E is use with the 30-50
MHz Monogram Portable radio. It is a continuous tone coded
squelch system (CTCSS) capable of utilizing all 37 standard
EIA tone frequencies to provide a degree of privacy in voice
communications and allow you to hear only those calls
intended for you. Additionally, a non-standard tone, 97.4 Hz
and a disabled state called "No Tone" are available. All are
programmed by channel and mode, transmit or receive. This
allows radios with Channel Guard to be programmed so that
each channel may have different encode/decode tones or may
have no encode or decode at all. T he subaudible tone assigned
to your transmit frequency precedes the voice message. Its
purpose is to activate the decoder and open the receiver to
allow the message to be heard. Table 1 identifies the standard
EIA CTCSS tones.
Operational control of the programmed Channel Guard
frequencies is controlled by an eight bit digital code sent
serially by the radio's microcomputer from the EEPROM to
the Channel Guard when the radio is first turned on, when the
channel is changed, and when the radio changes from receive
to transmit and transmit to receive modes.
The Channel Guard board contains a single IC (integrated
circuit) and associated discreet components mounted on a
printed circuit board. The PCB is located underneath the Top
Panel PCB and is plugged into the optio n interface connector
located on the main PCB. See Installation.
Table 1 Channel Guard Tone Frequencies
No. Freq. Hz No. Freq. Hz.
01 67.0 20 131.8
02 71.9 21 136.5
03 74.4 22 141.3
04 77.0 23 146.2
05 79.7 24 151.4
06 82.5 25 156.7
07 85.4 26 162.2
08 88.5 27 167.9
09 91.5 28 173.8
10 94.8 29 179.9
11 97.4 30 186.2
12 100.0 31 192.8
13 103.5 32 203.5
14 107.2 33 210.7
15 110.9 34 218.1
16 114.8 35 225.7
17 118.8 36 233.6
18 123.0 37 241.8
19 127.3 38 250.3
PINOUT/FUNCTIONS
PIN FUNCTION
1 PTT OUT - Connects to pin 2; allows PTT signal to pass through
2 PTT IN - Connects to pin 1; allows PTT signal to pass through
3 GND - ground
4 TX AF IN - Transmit audio input; allows CTCSS tones to be added
5 1 MHz - Frequency reference for U1.
6 + 5 Vdc - input power, 4.5 mA
7 DECODE - CTCSS decode state output to the radio; +5 Vdc indicates tone is present, 0 Vdc indicates it is not.
8 Not used
9 DATA - Data received from EEPROM to set tone frequency and mode (encode/decode)
10 SQ POT (dual purpose) - Grounded - disables the CTCSS decode function. Ungrounded - allows R6 to control the
radio's squelch threshold and enables the tone decode function
11 RX AF IN - Radio detector input from radio. Allows audio frequencies below 300 Hz to be filtered out and permits
CTCSS tone detection..
12 CLOCK - Used to shift data out of EEPROM. R8 &C4 delays data out so that the rising edge seen by U1 comes after
the data appears on pin 9.
13 STROBE/ENABLE - Input used to strobe data into its internal control register.
14 RF AF OUT - Receive audio, after U1 filters out the Channel Guard tones, to radio volume control.
15 TX AF OUT - Transmit audio, after Channel Guard tone has been added, to radio modulator.
16 PUSH TO MON - Not used by Channel Guard. Radio microprocessor monitors this signal and always unmutes the
receiver.
Copyright October 1993, Ericsson GE Mobile Communications Inc.
2
INSTALLATION
The Channel Guard Board plugs into the option interface
connector on the main printed circuit board and is located
below the top panel printed circuit board. Refer to Figure 1,
Channel Guard Installation.
1. Release the locking bolt securing the battery cover (back)
and remove cover.
2. Remove battery by pulling up on cloth tab attached to
battery.
3. On each side of the radio near the top, remove the two
posidrive screws securing bottom cover casting to the top
panel casting. One screw passes through the top of the
PTT bar.
4. Using a posidrive screw driver, remove the four machine
screws from the bottom cover (battery compartment) and
separate the bottom from the radio assembly to expose the
option interface board.
5. Remove the option interface board from the main printed
circuit board in the radio and plug in the Channel Guard
board. as shown in Figure 1.
LBI-39006
CA-1121 Sub-Audible Tone Encoder/Decoder
ALIGNMENT
6. Reassemble radio in reverse order.
7. Refer to the ALIGNMENT section in this manual and
complete the procedures given to set the noise squelch
threshold and the tone deviation.
CAUTION
Improper installation or pin misalignment may
result in damage to the radio and/or the tone
board.
NOISE SQUELCH THRESHOLD, 10 DB
SINAD
1. Complete normal radio alignment given in the radio
maintenance manual (LBI-38998 )and then select a
channel programmed for Channel Guard.
2. Set RF Test Set to the channel frequency and modulate it
with a 1 kHz tone and 3 kHz deviation.
3. Adjust the output level for 10 dB SINAD.
4. Enable the tone decoder by rotating the radio squelch
control counterclockwise until it clicks.
5. Monitor U7-13 on main printed circuit board with a DC
voltmeter and adjust R6 until the voltage just goes high
more then 2.5 Vdc)
6. Remove the RF signal and verify that pin 13 goes low
(less than 2.5 Vdc).
3
LBI-39006 Parts List
TONE DEVIATION ADJUSTMENT
1. Set RF Generator to channel frequency and modulate
with 1 kHz tone. Set deviation for 750 Hz. You should
hear the 1 kHz tone only when the Channel Guard tone is
present.
2. Set up the test equipment to check transmitter modulation
as directed in the radio maintenance manual.
3. Push the PTT bar and adjust R9 for the desired tone
deviation, normally 750 Hz.
PARTS LIST
Channel Guard Board
344A9730P27
SYMBOL PART NO. DESCRIPTION
C1 R29/130-185-5
C2 R29/130-153-5
C3 R29/130-158-0
C4 R29/131-027--0Capacitor, ceramic chip. 100 pF
D1 R29/243-027-4 Diode, switching MMBD914 (5D)
D2 R29/249-005-4 Diode, Schottkey MMBD101 (4M)
P1 R29/422-217-0 Header, 16 pin male
Q1 R29/218-018-2 Transistor, switching
R1 R29/060-272-7
R2 R29/060-223-3
R3 R29/060-474-3
R4 R29/060-105-0
R5 R29/060-103-8
R6 R29/074-223-7 Resistor, Trimmer 22k ohm
R7, R8 R29/060-103-8
R9 R29/074-473-6 Resistor, Trimmer 47k ohm
U1 R29/229-288-7 IC MX-365LH
Capacitor, ceramic chip. 0.1 µF
Capacitor, ceramic chip. 0.1 µF
Capacitor, ceramic chip. 0.001 µF
MMBT3904(1A)
Resistor, Chip 2.7k ohm ± 5%
Resistor, Chip 22k ohm ± 5%
Resistor, Chip 470k ohm ± 5%
Resistor, Chip 1M ohm ± 5%
Resistor, Chip 10k ohm ± 5%
Resistor, Chip 10k ohm ± 5%
4
OUTLINE & SCHEMATIC DIAGRAM LBI-39006
OUTLINE DIAGRAM
SCHEMATIC DIAGRAM
CHANNEL GUARD BOARD
349A9730P27
5
Ericsson Inc.
Private Radio Systems
Mountain View Road
Lynchburg, Virginia 24502
1-800-528-7711 (Outside USA, 804-528-7711) Printed in U.S.A.
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