LT-4200 - Connect Systems

CONNECT SYSTEMS INC.
1802 Eastman Ave. Suite 116
Ventura, Ca. 93003
Phone (805) 642-7184
Fax
(805) 642-7271
Model LT-4200
Trunked Repeater Manager
USER'S INSTRUCTION MANUAL
Made in U.S.A.
Copyright (C) 1996
By
Connect Systems Inc.
TABLE OF CONTENTS
Notices
........................................
LT-4200 Description
Overview .....................................
A Closer Look ................................
Managing the System with with your PC ........
Specifications ...............................
Connecting the LT-4200 to your Repeater
........
Set up and Adjustments
Setting the LT-4200 Jumpers ..................
Setting the Dip Switches .....................
Setting the Levels ...........................
Programming the LT-4200
........................
Definition of terms
............................
Circuit Description
............................
Warranty
.......................................
Schematic Diagrams
.............................
Connect Systems Inc. - Model LT-4200
Page 2
NOTICES
FEDERAL COMMUNICATIONS COMMISSION (FCC) REGULATIONS
Your LT-4200 complies with Part 15 of the FCC rules for a Class A
digital computing device. Operation is subject to the following
regulations:
1. This device may not cause harmful interferance.
2. This device must accept any interferance received, including
interferance that may cause undesired operation.
In order to assure that operation remains in compliance with FCC
Part 15, all repairs must be performed by CSI, or an authorized
CSI repair station.
COPYRIGHT NOTICE
The Printed Circuit Board, Cabinet Nomenclature, Operating
Software and CSI BASE are copyrighted and remains the exclusive
property
of
Connect
Systems,
Inc
(CSI).
Reproduction,
duplication, or disclosure is not permitted. No part of this
document may be copied or reproduced in any form without the
prior written consent of Connect Systems, Inc.
TRADEMARKS
LTR
EFJ
UNIDEN
CSI
CSI BUS
CSI BASE
is
is
is
is
is
is
a
a
a
a
a
a
registered
registered
registered
registered
registered
registered
trademark
trademark
trademark
trademark
trademark
trademark
of
of
of
of
of
of
E.F. Johnson Company
E.F. Johnson Company
Uniden America.
Connect Systems, Inc.
Connect Systems, Inc.
Connect Systems, Inc.
All manufacturer and product names used in this document are the
trademarks or registered trademarks of their respective owners.
Connect Systems Inc. - Model LT-4200
Page 3
LT-4200 DESCRIPTION
OVERVIEW
The CSI LT-4200 is a sophisticated dispatch only Trunking
Repeater Manager (Controller) for use on LTR trunked repeater
systems. The LT-4200 may be used with any combination of other
makes of dispatch or dispatch/interconnect controllers. The xx
provides up to 250 USER ID's per repeater. There may be up to 20
repeaters per system.
The LT-4200 "talks" to the other controllers on the system using
an LTR REPEATER BUS which the user must set for either EFJ or
Uniden protocol. In addition, CSI LT series controllers "talk"
amongst themselves using a second bus we call the "CSI BUS". The
CSI BUS allows the CSI controllers to perform advanced trunking
features unavailable in competing controllers and the ability to
program or download any CSI controller on the system through any
individual CSI controller. Thus a Modem connected to any CSI
panel gives programming and downloading control of all other CSI
controllers on the same system.
The CSI LT-4200 and LT-4900 are the only panels available with a
front panel LCD display that keeps you totally informed about
repeater and system status while you are at the repeater site.
User ID and other useful data are constantly displayed.
Another unique feature is a removable front panel that gives
access to all internal adjustments without removing the
controller from service or removing the controller from the rack.
Although the CSI LT-4200 and LT-4900 operate flawlessly with
other makes of controllers, the advanced features made possible
with the CSI BUS are good reasons to use CSI controllers
exclusively on each system you operate.
A CLOSER LOOK
Dispatch Logic Unit
The LT-4200 decodes and encodes digital trunking data to and from
the mobile units, routes conversations to other repeaters,
Connect Systems Inc. - Model LT-4200
Page 4
controls audio paths, maintains operator programmed talk limit
timers, and more.
The REPEATER BUS
compatibility.
can
be
user
set
for
EFJ
or
Uniden
bus
Airtime Accumulation
The LT-4200 accumulates four accounting functions for each of 250
homed User ID's regardless on which repeater(s) were used:
1. Hits
2. Hits
3. Time
4. Time
time.
during regular time. Up to 65,536.
during prime time. Up to 65,536
useage during regular time. Up to 4660 hours talk time.
useage during prime time time. Up to 4660 hours talk
The LT-4200 also keeps track of attempted useage by invalid User
ID's.
Separate storage of regular time and prime time useage allows CSI
BASE to give you the option of prime time billing which also
helps control loading during peak use hours. Time accumulation is
maintained to the nearest second.
In addition, all necessary data is stored allowing you to view
repeater loading statistics in both data and graphical form on
your computer for:
1. The past 24 hours. Or,
2. Midnight to present time.
Validator
The built-in validator will only allow access to mobiles with
enabled User ID's. The validator in your LT-4200 will also
validate users on other makes of controllers that lack their own
validator.
Site Monitor
The site monitor allows you to graphically view the activity of
all channels on your system (even the channels with brand X
panels) while running CSI BASE on your PC. The PC may be
connected to to either RS-232 port of any LT-4200 or LT-4900 on
the system (or use a MODEM as explained below for remote
viewing).
You will see the repeater number, the mobile (home ID) using that
channel, the type of call (dispatch or interconnect), and how
long that dispatch has been in progress. If the mobile has been
Connect Systems Inc. - Model LT-4200
Page 5
invalidated in the data base, a home=21 will appear on the
screen. If the repeater is busied up to send the station ID or
because of a cross busy condition, a 253 will appear in the ID
field.
Modem
An external 1200/2400 Baud modem may be connected to the front or
rear RS-232 port on any LT-4200 on your system. All other LT4200's on the system can be accessed via this single modem using
a standard end to end phone line.
NOTE: If you have even one LT-4900 on the system, you can use
it's built-in modem to access all of your LT series panels.
IMPORTANT: Having RS-232 ports on both the front and rear panel
is a convenience only. YOU MAY ONLY CONNECT AND USE ONE AT A
TIME.
MANAGING THE SYSTEM WITH YOUR PC
Your system is totally managed using CSIBASE, a software
application for your PC. CSIBASE runs either under DOS or using a
DOS window from WINDOWS. CSIBASE will manage all of the
individual repeaters (with LT series panels) in a system and also
manage all of your systems running with LT series controllers.
You have total control of all LT series panels on each system
from any RS-232 port or remotely using an external modem
connected to any LT-4200 or the built in modem in any LT-4900.
CSIBASE stores the set up parameters of all repeaters on each
system. You may review the set up, edit to any extent you wish
off line, then quickly transfer new programming data and/or
download billing data with a quick call. Your LT-4200 can service
mobile users and on line programming simultaneously, therefore
there is no interrruption of service while you are programming or
site monitoring.
CSIBASE also incorporates a site monitoring capability which
allows you to view the entire operation of a system from your
office, or use the convenient histograms to analyze loading etc.
It may be very convenient to have a laptop connected to an RS-232
port when you are at the site so you are totally aware of what
the system is doing at all times. (The front panel LCD displays
also keep you informed).
CSIBASE can generate customer invoices, or "export" billing files
to your favorite accounting application. Call CSI for assistance
if required.
Connect Systems Inc. - Model LT-4200
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SPECIFICATIONS
(probably should have more specs)
Mechanical
Height
Width
Depth
Weight
1.75 inch
19
inch
6.9 inch
lbs.
Power Requirements
DC Input Voltage
DC Input current
+10 to +16 Vdc
TBD, approx 200 Ma max
Interface to the Rx and Tx
Connector
Phoenix
12 Pin
P/N MSTB2.5/12ST-5.08
Mating Plug
Phoenix
12 Pin
P/N MSTBA2.5/12G-5.08
Connections
DC Power, GND, TX AUD, TX KEY, RX DET, TX SUB, RX
COS, AUX RLY, AUX RLY, SENSE 1, SENSE 2
TX AUD 0 - 5 Vpp in two selectable ranges.
Output impedance = 1K ohm.
Connect Systems Inc. - Model LT-4200
Page 7
TX KEY
Selectable sink to gnd, or pull to +12Vdc.
0.5 Amp maximum.
RX DET 15mV - 10V in two selectable ranges. Has de-emphasis
built-in. Input impedance = 150K ohms.
TX SUB
RX COS
AUX RLY
0 - 5V pp in two selectable ranges.
Output impedance = 5.1K ohms
0 - 10 V. Adjustable threshold point. Selectable
polarity. Input impedance = 100K ohms.
Selectable NO or NC contacts. 0.5 amp DC maximum.
SENSE 1
Used as cross busy input. A logic high instructs
the LT-4200 to operate normally. A low instructs
the LT-4200 to be busy.
Low <= 1V. High >= 2V. Input impedance = 2.2k ohms
pulled up to +5 Vdc.
SENSE 2
Low <= 1V. High >= 2V. Input impedance = 2.2k ohms
pulled up to +5 Vdc.
Interface to the other Repeater Controllers
RPTR BUS
CSI BUS
Uses EFJ or Uniden protocol.
(User selectable).
All system controllers are interfaced with RG-58
coax fitted with BNC connectors.
Uses proprietary Connect Systems, Inc. protocol.
All CSI LT series controllers are interfaced with
RG-58 coax fitted with BNC connectors.
Connect Systems Inc. - Model LT-4200
Page 8
CONNECTING THE LT-4200 TO YOUR REPEATER
Interface the LT-4200 to the Rx and Tx via the 12 pin connector.
Use shielded wiring for all connections (be sure to connect all
shields to GND). For your convenience, the plug is removable:
RX DET:
The RX DET input terminal must be connected directly (do
not use a coupling capacitor) to the receiver
discriminator (de-modulator) output.
RX COS:
NOTE: You have a choice of either using the LT-4200
noise squelch or, if you prefer, to use the squelch
built into the receiver. We recommend using the LT-4200
noise
squelch
and
not
bothering
with
the
COS
connection. The choice is yours. To use the noise
squelch, simply remove JP13. If you wish to make a COS
connection and use the Rx internal squelch, use the
following directions:
Connect Systems Inc. - Model LT-4200
Page 9
Connect to a point that has good voltage swing when the
squelch is opened/closed. The best point to connect is
to the collector of the transistor that controls the
busy light (if the receiver has one). Otherwise, you
may connect to the squelch gate control voltage. Your
last choice would be to connect to output of the noise
rectifier.
If the point selected goes more positive (voltage
increases) when a signal is received, strap JP-13center
to the + side. If the point goes to a lower voltage,
strap JP-13 from center to the - side.
When the COS threshold control P3 has been properly
adjusted (see page zz), and JP-13 properly strapped
(see page zz), the front panel LCD will indicate RX
when a signal is received. This condition must be
achieved for proper operation of the LT-4200.
NOTE: The squelch control in the receiver must be set
for quiet (squelched) receive. Set the squelch as you
would any squelch, but remember if you set it too tight
receive sensitivity may suffer.
TX AUD: Connect to the transmitter voice audio input.
TX KEY:
Connect to the transmitter PTT line.
TX SUB:
The TX SUBTONE output is used to inject the digital
subcarrier directly into the transmitter modulator.
This injection point must be past IDC and must not
interfere with the voice modulation.
NOTE: Only true FM (frequency modulation) can be used
for the digital modulation of the transmitter.
+12 VDC:
Connect to a source of 12-16 Vdc. The LT-4200 is
reverse polarity protected, so a polarity mistake will
not damage your LT-4200. Connect the return lead (-) to
GND.
SENSE 1:
Is used as the Cross Busy input. The input is
compatible with CMOS, TTL or open collector logic
levels.
SENSE 2:
Is a spare input, not yet defined. The input is
compatible with CMOS, TTL or open collector logic
levels.
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10
Page
AUX RLY:
Used only for special applications. JP-1 allows
selection of NO or NC operation. Do not exceed .5 amp
contact current.
The following connections are required to the other repeater
controllers on the system:
RPTR
BUS
BNC female. All controllers on a system must be
connected in a daisy chain with RG-58 fitted with
BNC's. Use BNC "T" adapters as necessary to complete
the daisy chain.
NOTE:
CSI BUS
The LT-4200 must be configigured for EFJ
Uniden bus compatibility. See page zz JP-??.
or
BNC female. All LT-4200's and LT-4900's on a system
must be connected in a daisy chain with RG-58 fitted
with BNC's. Use BNC "T" adapters as necessary to
complete the daisy chain.
NOTE: Do not attempt to connect the CSI BUS to the
SUBSCRIBER BUS on Zetron panels or to any any other
product.
####################
WARNING
####################
The LT-4200 contains a power supply sensing circuit that
continuously monitors the input supply voltage. An instantaneous
drop below 10 VDC will cause a microcomputer reset. If the power
supply has poor regulation, erratic operation may result.
The purpose of the input voltage sensor is to protect the random
acceess memory (RAM) during power up and power down.
If erratic operation is observed be suspicious of poor regulation
from the power supply.
#########################################################
SET UP AND ADJUSTMENTS
SETTING THE LT-4200 JUMPERS
Connect Systems Inc. - Model LT-4200
11
Page
Prior to attempting adjustments or operation, all jumpers and dip
switches must be properly selected.
JP-1
Relay contact selector. The auxilliary relay (RL1) can be
set for NO or NC contacts available on the interface
connector (labelled, AUX RLY). Simply install the strap
center to NO for normally open or, center to NC for
normally closed.
JP-2 These four jumpers configure the LT-4200 for EFJ or Uniden
JP-3 bus compatibility. Put all four jumpers in position E for
JP-4 EFJ based systems or, put all four in position U for Uniden
& based systems.
JP-5
NOTE: It is very important that all four of these jumpers
are in the same position. All in E or, all in U! DO NOT
MIX!
JP-6 Selects the termination resistor for the CSI BUS. This bus
must be terminated in only one of your LT series
controllers per system.
For LT series units which are not to be terminations for
the CSI BUS, Put the jumper in position O (open).
The one LT unit selected as the system CSI BUS termination
must have the jumper in position E if used on an EFJ based
system or, put in position U if used on a Uniden based
system.
JP-7
Is the termination resistor for the RPTR BUS. This bus must
be terminated in only one controller on the system.
For units which are not to be terminations for the RPTR
BUS, Put the jumper in position O (open).
The one unit selected as the RPTR BUS termination must have
the jumper in position E if used on an EFJ based system or,
put in position U if used on a Uniden based system.
JP-8
Rx Polarity. A variety of factors can cause the digital
subcarrier to be received "inverted". This causes the
digital data to be undecodable. 'Strap in' is normal
polarity, strap removed is inverted and corrects receiver
inversion. If the mobile data can not be decoded after
adjusting the PREAMP (see page zz) try the inverse polarity
by removing JP-8.
JP-9
Tx Polarity. A variety of factors can cause the repeater
digital subcarrier to be transmitted "inverted". This
Connect Systems Inc. - Model LT-4200
12
Page
causes the digital data to be undecodable in the mobiles.
Strap in is normal polarity, strap removed is inverted and
corrects transmitter inversion. If the repeater data can
not be decoded try the inverse polarity by removing JP-8.
JP-10 does not apply
JP-11 TX KEY Polarity. This strap gives you a choice of pull to
GND, or pull to POS (+12 VDC) for transmitter keying.
JP-12 Is not used on the LT-4200 and should be left open.
JP-13 COS Polarity Select. This strap must be removed if using
the LT-4200 noise squelch. To enable COS operation, simply
install JP-13 connecting the center pin and the desired COS
polarity. The polarity (+/-) is marked adjacent to JP13.
NOTE: See the COS adjustment P3
infromation on polarity selection.
on
page
zz
for
more
JP-14 does not apply
JP-15 Coarse PRE-AMP gain select strap: When strapped the PRE-AMP
is operating at lowest gain. Try to complete the PRE-AMP
adjustment with the strap installed. Only remove JP-15 if
the desired level measured at TP3 can not be achieved.
JP-16 LED Power: Removal eliminates power to LED's (e.g. Power
LED on the front panel). Used to conserve power in solar
powered installations.
JP-17 TX AUDIO Output level strap. The audio output is selectable
in two ranges. With the strap installed, the audio out is
0-1 volt. With the strap removed, the output range is 0-5
volts. The strap should be installed in most installations.
JP-18 DCS (Digital Coded Subcarrier) Level strap. The TX SUB
output level is selectable in two ranges. With the strap
installed, the level is 0-1 volt. With the strap removed,
the output range is 0-5 volts. The strap should be
installed in most installations.
Connect Systems Inc. - Model LT-4200
13
Page
SETTING THE DIP SWITCHES
Your LT-4200 has an eight position dip switch and a four position
dip switch. Here are the four functions conrolled by the eight
position switch:
Sw Pos
Pos 1.
Pos 2.
Pos 3.
Pos 4.
Pos 5.
Pos 6.
Pos 7.
Pos 8.
Function
Repeater number
Repeater number
Repeater number
Repeater number
Repeater number
Area bit
Validation
Test
bit
bit
bit
bit
bit
1
2
4
8
16
Physical
1 1 1 1 1 1 1 1 -
Position
0
0
0
0
0
0
0
0
The four position switch controls three functions:
Sw Pos
Pos 1.
Pos 2.
Pos 3.
Pos 4.
Function
RS-232 Baud rate bit 1
RS-232 Baud rate bit 2
RNDL Master:
CSI MASTER:
Physical
1 1 1 1 -
Position
0
0
0
0
Dip switch setting procedure
The LT-4200 has been programmed to allow the front panel LCD
display to assist you in setting the dip switches. Watch the
display and you simply can't go wrong!
Begin by turning on the LT-4200 by applying 12 Vdc power. To get
into the dip switch setting mode, put all five switches that
control the Repeater number into logic 0 (to the right) and tap
the CPU reset button SW3. The LCD will now display "INVALID
REPEATER". As soon as you begin to set the repeater number, the
LCD will change screens and show all seven of the current dip
switch settings. You can now change switch settings in any order
you like.
Resetting all Parameters to Factory default settings
Connect Systems Inc. - Model LT-4200
14
Page
The factory default settings for all programmable parameters
be restored by placing all five of the repeater number
switches into the 1 position (to the left) and tapping the
reset button (SW3). Afterward, you will have to follow the
switch setting prodedure to restore these dip switches to
correct repeater number.
can
dip
CPU
dip
the
8 Position Dip Switch
Repeater number
Each repeater must be assigned a unique repeater number 1 - 20.
Here are the binary codes:
Sw Pos
Pos 1.
Pos 2.
Pos 3.
Pos 4.
Pos 5.
Repeater Number
0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0
----------------------------------------| 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
| 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0
| 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1
| 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0
| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
You can almost "feel" the five binary switches into the position
you desire because the computer is constantly converting the
binary dip switch setting and displaying the repeater number as a
two digit decimal number on the LCD.
NOTE: Five dip switches can set the decimal equivalent to numbers
0 - 31. However only 1 - 20 are valid repeater numbers. Do not
set to a number outside of this range.
Area Bit
The area bit is set to 1 or 0 as desired to match the area bit
settings of the mobiles. The LCD will show: "A# 1" or, "A# 0".
Pos 6.
Area bit
1
0
Validation
Set whether this LT-4200 should be used as a validator for other
controllers not equipped with a validator. The LCD will show a
capital "V" if enabled, a lower case "v" if disabled.
Pos 7.
Validation
1 = Enabled
Connect Systems Inc. - Model LT-4200
15
0 = Disable
Page
Test
Test causes the LT-4200 to send a steady stream of Sub Code data
so that you can easily set the TX SUB modulation, or for other
test pusposes. The LCD will show a capital "T" if in test mode, a
lower case "t" if not in test mode.
Pos 8.
Test
1 = on
0 = off
4 Position Dip Switch
RS-232 Baud rate
The baud rate can be set to 300, 1200, 2400, 4800. The LCD will
show e.g. B=2400 if the baud rate is currently set for 2400
bits/second.
Baud Rate
1 2 4
3 2 4 8
0 0 0 0
0 0 0 0
Sw Pos --------Pos 1. | 0 1 0 1
Pos 2. | 0 0 1 1
Repeater Bus (RNDL) Master
Any controller (regardless of make) on the system can be the
Repeater Bus MASTER. (BE SURE ONLY ONE CONTROLLER IS SET TO BE
THE REPEATER BUS MASTER). The LCD will show a capital "R" if
enabled or, a lower case "r" if disabled.
Pos 3.
RNDL Master
1 = MASTER ON
0 = off
CSI BUS Master
Any LT series repeater on the system can be the CSI BUS MASTER.
(BE SURE ONLY ONE CSI LT SERIES CONTROLLER IS SET TO BE THE CSI
BUS MASTER). The LCD will show a capital "C" if enabled or, a
lower case "c" if disabled.
Pos 4.
CSI MASTER
1 = MASTER
Connect Systems Inc. - Model LT-4200
16
0 = off
Page
SETTING THE LEVELS
P1
PREAMP: The PREAMP control is used to match the audio level
from your receiver to the LT-4200. To adjust, a
signal containing LTR subcode with about 1Khz
deviation must be applied to the receiver. Adjust
the PREAMP control until a level of 1V P-P is
observed at TP-3 using an oscilloscope.
An alternate (but less accurate) method of PREAMP
adjustment is to apply a signal containing LTR
subcode and advance the PREAMP adjustment CW from
its fully CCW position until the LVL LED
(adjacent to the PREAMP control) just begins to
flash. Stop at the point where regular flashing
occurs. The LVL LED will also flash on noise when
there is no signal, disregard.
This completes the adjustment of the PREAMP
control.
Future
adjustment
should
only
be
required if the LT-4200 is connected to a
different receiver.
P2
SQUELCH:
NOTE: If JP13 has been strapped for COS
operation, then P2 is not used and has no effect.
P2 is set like a conventional squelch control.
The RX icon on the LCD will come on when the
squelch setting is below threshold or, when a
signal is received.
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Page
P3 COS:
NOTE: If JP13 has been strapped for noise squelch
operation, then P3 is not used and has no effect.
The COS control sets the COS input threshold
level. Measure the voltage at TP-2 with no
signal, then measure the voltage again with a
signal applied. Adjust the COS control until the
voltage reading at TP-3 is approximately midway
between the two readings previously obtained at
TP-2.
For example: If TP-2 read 2 volts with no signal,
and 4 volts with a signal applied to the
receiver, TP-3 would be set to read 3 volts.
IMPORTANT: If the COS polarity select strap JP13
is set correctly and the COS control is properly
adjusted, the RX icon in the LCD will illuminate
when there is a signal, and will go out when the
signal is removed.
P4 DCS:
P6
The DIGITAL CODED SUBCARRIER control sets the
modulation level of the subcarrier on the TX SUB
output.
RPT AUDIO: The REPEAT AUDIO control sets the level of the
voice audio. Set so that 3 khz. input deviation
causes 3 khz. output deviation. This will cause a
linear input/output relationship.
NOTE: The RPT AUDIO control should only be
adjusted after the PREAMP control has been
properly adjusted.
P7 DTMF:
The DTMF control adjusts the deviation of the
outgoing regenerated DTMF. Set for about 2.5 KHz.
deviation.
P8 SIGNAL 1:
Adjust for the desired CW ID modulation level.
NOTE: P5, P6, P9, P10, are not used in the LT-4200.
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Page
DEFINITION OF TERMS
this is left over stuff
Courtesy beep: A brief tone at the end of a mobiles transmission
that lets the other mobile know that it is their turn to reply.
CW ID: Automatic identification of call sign in Morse Code.
Stuck
Mic.
activity
timer:
Sets
the
maximum
continuous
(uninterrupted) talk time. If a user talks past the activity
timer time, the repeater merely stops transmitting until the
input drops and is picked up anew.
RX polarity: Design characteristics of the repeater receiver
design can invert the received digital subcarrier from the
mobiles precluding decoding. The LT-4200 has the ability to
invert the SubCode in software by removing JP-8 in essence
correcting the unwanted inversion of the receiver. (see page zz).
TX polarity: Design characteristics of the repeater transmitter
design can invert the digital subcarrier precluding decoding in
the mobiles. The LT-4200 has the ability to invert the SubCode in
Connect Systems Inc. - Model LT-4200
19
Page
software by removing JP-9 in essence correcting the unwanted
inversion of the transmitter. (see page zz).
User Enable/Disable: Ability to turn a subscriber off for non
payment and back on in response to payment. Sometimes it may be
desirable to put a subscriber into reserve tone status rather
than use the deadbeat disable. That way he will realize that he
is picking up the repeater but can't talk. This may give the user
a clue that they need to write a check.
CIRCUIT DESCRIPTION
ANALOG CIRCUITS
The audio path
The incoming audio is buffered, de-emphasized and amplified to
the amount set by the PREAMP control by input op amps U35. The
audio then proceeds to a five pole low pass filter and a six pole
high pass filter. The low pass filter U36 removes voice audio and
extracts the mobile digital subcarrier for detection at the
adaptive centering differential comparator. The comparator output
(RX-SUBTONE) is fed to the subcarrier decoder CPU U8 for software
detection and error correction. The six pole high pass filter
U35/U36 removes the digital subcarrier data from the incoming
audio to avoid the buzzing sound that would result if it were not
Connect Systems Inc. - Model LT-4200
20
Page
removed. The audio from the high pass filter continues through
the squelch switch U46A, through the RPT level control and then
on to the audio output amplifier U48A.
COS and noise squelch
The noise squelch is derived by passing the PREAMP output through
a five pole high pass filter U37A/U37B which eliminates all voice
band power. The filtered noise is then amplified by U37C whose
gain is adjusted by the squelch control P2. The filtered noise is
then full wave rectified by D13/D14
and detected by U40B then
sent through R87 to inverter U26B.
The COS input is buffered by U40C and compared using U40D to a
reference voltage with which is set by the COS threshold pot P3.
The output then proceeds to the polarity select strap JP-13.
If JP-13 is not strapped, the noise squelch is active. If JP-13
is installed in either polarity, the COS overwhelms the noise
squelch due to the presence of R87. The resultant carrier
detection (REC) is sent to the main CPU U15.
(((((((((((( Left off here )))))))))))))
DTMF and MF decoding
DTMF is decoded and regenerated by U49 with the assistance of CPU
MF
is decoded by U34. When either occurs
The with some assistance from the microcomputer U12.
DCS is generated directly by the microcomputer U12. CTCSS
generated by waveform generator U16. The microcomputer
controls the U16 waveform generator via pins 34,35 and 36.
and CTCSS have separate level controls the output of each is
to summation amplifier and four pole low pass filter U4.
output of U4 feeds the transmitter modulator with SUBTONE.
is
U12
DCS
fed
The
The PTT circuit consists of Q6, Q14 and Q20. This circuit is
controlled by the microcomputer U12 via pin 7. A polarity select
strap gives the choice of ground keying or plus keying.
A power on reset circuit consisting of Q21 and associated
components monitors the input voltage and quickly halts the
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microcomputer if the applied input voltage is too low. The power
on reset circuit provides proper computer start up after power is
applied and protects the EE memory U13 on power down.
Counters U22 and U23 divide the 448 KHz clock from U11 and allow
remote re-booting of the microprocessor when any incoming DTMF
digit exceeds 9 seconds in duration. At the end of nine seconds
U22 pin 15 turns on transistor Q9 which in turn enables the power
on reset circuit.
The front panel digital display U6-U9 are controlled by the
display driver U5. The microcomputer U12 talks to U5 via pins
37,38 and 39.
Incoming power is fed through reverse polarity protect diode D8
and then fuse F1. From there the +V voltage feeds a +5 volt
regulator U20 used by the digital components. Another smaller +5
volt regulator U21 is used to supply bias and reference voltage
to the analog op-amps etc.
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