Comtech EF Data CDM-500 User manual

Part Number MN/CDM500.IOM Revision 1.3
CDM-500
Satellite Modem
Installation and O
p
eration Manual

Copyright © Comtech EFData, 2000. All rights reserved. Printed in the USA.
Comtech EFData, 2114 West 7th Street, Tempe, Arizona 85281 USA, [phone], FAX: [phone].
CDM-500
Satellite Modem
Installation and Operation Manual
Part Number MN/CDM500.IOM
Revision 1.3
July 10, 2000
Comtech EFData is an ISO 9001
Registered Company.

Copyright © Comtech EFData, 2000. All rights reserved. Printed in the USA.
Comtech EFData, 2114 West 7th Street, Tempe, Arizona 85281 USA, [phone], FAX: [phone].
Customer Support
Contact the Comtech EFData Customer Support Department for:
• Product support or training
• Information on upgrading or returning a product
• Reporting comments or suggestions concerning manuals
A Customer Support representative may be reached at:
Comtech EFData
Attention: Customer Support Department
2114 West 7th Street
Tempe, Arizona 85281 USA
[phone] (Main Comtech EFData Number)
[phone] (Customer Support Desk)
[phone] FAX
or, E-Mail can be sent to the Customer Support Department at:
[e-mail]
Contact us via the web at www.comtechefdata.com.
1. To return a Comtech EFData product (in-warranty and out-of-warranty) for
repair or replacement:
2. Request a Return Material Authorization (RMA) number from the Comtech
EFData Customer Support Department.
3. Be prepared to supply the Customer Support representative with the model
number, serial number, and a description of the problem.
4. To ensure that the product is not damaged during shipping, pack the product in
its original shipping carton/packaging.
5. Ship the product back to Comtech EFData. (Shipping charges should be prepaid.)
For more information regarding the warranty policies, see Error! Reference source not
found., p. Error! Bookmark not defined..

CDM-500 Satellite Modem Preface
Rev. 1.3 i
Table of Contents
Customer Support........................................................................................................................................................ i
About this Manual .................................................................................................................................................... vii
Conventions and References...................................................................................................................................vii
Cautions and Warnings ......................................................................................................................................vii
Metric Conversion..............................................................................................................................................vii
Reporting Comments or Suggestions Concerning this Manual..............................................................................vii
SAFETY NOTICES.................................................................................................................................................viii
Electrical Safety.....................................................................................................................................................viii
Fuses......................................................................................................................................................................viii
Environmental..........................................................................................................................................................viii
Installation.................................................................................................................................................................. ix
Telecommunications Terminal Equipment Directive............................................................................................. ix
EMC (Electromagnetic Compatibility).................................................................................................................... ix
Warranty Policy.......................................................................................................................................................... x
Limitations of Warranty ........................................................................................................................................... x
Exclusive Remedies.................................................................................................................................................. x
CHAPTER 1. INTRODUCTION.................................................................................1–1
1.0 Introduction.................................................................................................................................................. 1–1
CHAPTER 2. INSTALLATION ..................................................................................2–1
2.0 Unpacking..................................................................................................................................................... 2–1
2.1 Mounting....................................................................................................................................................... 2–1

Preface CDM-500 Satellite Modem
ii Rev. 1.3
2.2 Configuration................................................................................................................................................ 2–2
2.3 Select Internal IF Loop................................................................................................................................ 2–2
2.4 Connect External Cables ............................................................................................................................. 2–2
CHAPTER 3. FUNCTION..........................................................................................3–1
3.0 Functional Description................................................................................................................................. 3–1
CHAPTER 4. PHYSICAL DESCRIPTION.................................................................4–1
4.1 Front Panel ................................................................................................................................................... 4–1
4.2 Rear Panel..................................................................................................................................................... 4–3
CHAPTER 5. CONNECTOR PINOUTS.....................................................................5–1
5.1 Connector Pinouts........................................................................................................................................ 5–1
5.1.1 Data Connector - 25 Pin ‘D’ Type Female..............................................................................................5–1
5.2 Alarms Connector - 15 Pin ‘D’ Type Male................................................................................................. 5–2
5.3 Remote Control Connector - 9 Pin ‘D’ Type Male.................................................................................... 5–3
5.4 Auxiliary Serial Connector - He1402 3 Pin Header .................................................................................. 5–3
CHAPTER 6. FRONT PANEL OPERATION.............................................................6–1
6.1 Description.................................................................................................................................................... 6–1
6.2 Menu Trees................................................................................................................................................... 6–3
6.3 OPENING SCREEN.................................................................................................................................... 6–4
6.4 SELECT........................................................................................................................................................ 6–4
6.5 CONFIG: ...................................................................................................................................................... 6–5
6.5.1 (CONFIG) TX (Transmit) ......................................................................................................................6–5
6.5.2 (CONFIG, TX) MOD (Modulation).......................................................................................................6–6
6.5.3 (CONFIG, TX) FREQ (Frequency)........................................................................................................6–6
6.5.4 (CONFIG, TX) DATA (Data Rate)........................................................................................................ 6–6
6.5.5 (CONFIG, TX) FEC (Forward Error Correction)...................................................................................6–6
6.5.6 (CONFIG, TX) ON/OFF........................................................................................................................ 6–6
6.5.7 (CONFIG, TX) PWR (Power)................................................................................................................6–7
6.5.8 (CONFIG, TX) SCRAM (Scrambling) .................................................................................................. 6–7
6.5.9 (CONFIG, TX) CLK (Clocking)............................................................................................................ 6–7
6.5.10 (CONFIG, TX) TSI (Transmit Spectral Invert) ................................................................................6–7
6.5.11 (CONFIG) RX (Receive) ................................................................................................................... 6–8
6.5.12 (CONFIG, RX) MOD (Modulation).................................................................................................. 6–8
6.5.13 (CONFIG, RX) FRQ (Frequency)......................................................................................................6–8

CDM-500 Satellite Modem Preface
Rev. 1.3 iii
6.5.14 (CONFIG, RX) DATA (Data Rate) ...................................................................................................6–8
6.5.15 (CONFIG, RX) FEC (Forward Error Correction).............................................................................. 6–8
6.5.16 (CONFIG, RX) ACQ (Acquisition sweep range) .............................................................................. 6–9
6.5.17 (CONFIG, RX) DESCRAM (Descrambler).......................................................................................6–9
6.5.18 (CONFIG, RX) CLK (Clocking).........................................................................................................6–9
6.5.19 (CONFIG, RX) BUF (Buffer size).................................................................................................... 6–10
6.5.20 (CONFIG, RX) RSI (Receive spectral inversion)............................................................................. 6–10
6.5.21 (CONFIG, RX) Eb/No (Eb/No Alarm)............................................................................................. 6–10
6.5.22 (CONFIG) FRAME (Framing Mode)............................................................................................... 6–10
6.5.23 (CONFIG, FRAME) TRANSPARENT............................................................................................ 6–10
6.5.24 (CONFIG, FRAME) FRAMED........................................................................................................ 6–11
6.5.25 (CONFIG, FRAME, FRAMED) EDMAC-ON.................................................................................6–11
6.5.26 (CONFIG, FRAME, FRAMED, ON) EDMAC MASTER...............................................................6–11
6.5.27 (CONFIG, FRAME, FRAMED, ON) EDMAC SLAVE.................................................................. 6–12
6.5.28 (CONFIG) INTFC (Interface)........................................................................................................... 6–12
6.5.29 (CONFIG) REMCONT (Remote control).........................................................................................6–12
6.5.30 (CONFIG, LOCAL).......................................................................................................................... 6–12
6.5.31 (CONFIG, REMOTE)....................................................................................................................... 6–12
6.5.32 (CONFIG, REMOTE, BAUD)..........................................................................................................6–13
6.5.33 (CONFIG, REMOTE, INTFC) ......................................................................................................... 6–13
6.5.34 (CONFIG, REM, INTFC, ADDR) RS232 BUS ADDRESS........................................................... 6–13
6.5.35 (CONFIG, REM, INTFC, ADDR) RS485 BUS ADDRESS:.......................................................... 6–13
6.5.36 (CONFIG) MASK (Alarm mask)..................................................................................................... 6–13
6.5.37 (CONFIG, MASK) AGC ................................................................................................................. 6–14
6.5.38 (CONFIG, MASK) Eb/No ................................................................................................................ 6–14
6.5.39 (CONFIG, MASK) RX-AIS .............................................................................................................6–14
6.5.40 (CONFIG, MASK) BUF-SLIP (Buffer slip).....................................................................................6–14
6.5.41 (CONFIG, MASK) TX-AIS..............................................................................................................6–15
6.5.42 (CONFIG) IMPED (IF impedance) .................................................................................................. 6–15
6.6 TEST ........................................................................................................................................................... 6–16
6.7 INFO (Information) ................................................................................................................................... 6–17
6.7.1 (INFO) ID (Circuit ID).......................................................................................................................... 6–17
6.7.2 (INFO) TX (Transmit information)....................................................................................................... 6–17
6.7.3 (INFO) RX (Receive information) ........................................................................................................6–17
6.7.4 (INFO) BUFF (Buffer information) ......................................................................................................6–18
6.7.5 (INFO) EDMAC (Framing and EDMAC information)......................................................................... 6–18
6.7.6 (INFO) REMCONT (Remote Control information).............................................................................. 6–18
6.7.7 (INFO) MASK (Alarm mask information)............................................................................................ 6–18
6.7.8 (INFO) MISC (Miscellaneous information).......................................................................................... 6–19
6.8 MONIT (Monitor)...................................................................................................................................... 6–20
6.8.1 (MONIT) ALARMS.............................................................................................................................. 6–20
6.8.2 (MON, ALARMS) UNIT (Unit alarms)................................................................................................ 6–20
6.8.3 (MON, ALARMS) RECEIVE (Receive alarms)...................................................................................6–20
6.8.4 (MON, ALARMS) TRANSMIT (Transmit alarms)..............................................................................6–20
6.8.5 (MONIT) STORED EVENTS............................................................................................................... 6–21
6.8.6 (MON, EVENTS) VIEW ...................................................................................................................... 6–21
6.8.7 (MONIT) RX-PARAMS (Receive Parameters).................................................................................... 6–22
6.9 STORE/LD (Store/Load)........................................................................................................................... 6–23
6.9.1 (STORE/LD) STORE............................................................................................................................6–23
6.9.2 (STO/LD) LOAD .................................................................................................................................. 6–23

Preface CDM-500 Satellite Modem
iv Rev. 1.3
6.10 UTIL (Utility) ............................................................................................................................................. 6–25
6.10.1 (UTIL) SET-RTC (Set real-time clock)............................................................................................6–25
6.10.2 (UTIL) DISPLAY (Display brightness)............................................................................................ 6–25
6.10.3 (UTIL) MAN-1:1 (Manual 1:1 switchover)...................................................................................... 6–25
6.10.4 (UTIL) RECENTER-BUF (re-center buffer).................................................................................... 6–25
6.10.5 (UTIL) ID (Circuit ID)......................................................................................................................6–26
CHAPTER 7. CLOCKING .........................................................................................7–1
7.1 Transmit Clocking........................................................................................................................................ 7–1
7.1.1 Internal Clock.......................................................................................................................................... 7–1
7.1.2 External Clock......................................................................................................................................... 7–1
7.1.3 Loop-Timed............................................................................................................................................. 7–2
7.2 Receive Clocking .......................................................................................................................................... 7–2
7.2.1 Buffer Disabled .......................................................................................................................................7–2
7.2.2 Buffer Enabled, Rx=Tx...........................................................................................................................7–2
7.2.3 Buffer Enabled, Rx<>Tx.........................................................................................................................7–2
7.3 X.21 Notes..................................................................................................................................................... 7–2
CHAPTER 8. EDMAC CHANNEL.............................................................................8–1
8.1 Theory Of Operation ................................................................................................................................... 8–1
8.2 M&C Connection ......................................................................................................................................... 8–2
8.3 Setup Summary............................................................................................................................................ 8–3
APPENDIX A. SUMMARY OF SPECIFICATIONS.................................................... A–1
A.1 Modulator.....................................................................................................................................................A–1
A.2 Demodulator.................................................................................................................................................A–2
A.3 Data Interfaces..............................................................................................................................................A–3
A.4 Miscellaneous................................................................................................................................................A–3
A.5 Approvals......................................................................................................................................................A–3
APPENDIX B. REMOTE CONTROL.......................................................................... B–1
B.1 Introduction..................................................................................................................................................B–1
B.2 EIA-485 .........................................................................................................................................................B–1
B.3 EIA-232 .........................................................................................................................................................B–2
B.4 Basic Protocol...............................................................................................................................................B–2

CDM-500 Satellite Modem Preface
Rev. 1.3 v
B.5 Packet Structure...........................................................................................................................................B–3
B.5.1 Start Of Packet ....................................................................................................................................B–3
B.5.2 Address................................................................................................................................................B–3
B.5.3 Instruction Code..................................................................................................................................B–4
B.5.4 Instruction Code Qualifier...................................................................................................................B–4
B.5.5 Message Arguments............................................................................................................................B–5
B.5.6 End Of Packet .....................................................................................................................................B–5

Preface CDM-500 Satellite Modem
vi Rev. 1.3
Figures
FIGURE 1-1 CDM500 PHOTO...............................................................................................................................1–1
FIGURE 4-1 FRONT AND BACK PANELS.........................................................................................................4–2
FIGURE 6-1 PRINCIPLE MENU TREE................................................................................................................ 6–3
FIGURE A-1 BER VITERBI DECODING............................................................................................................ A–4
Tables
TABLE 4-1- FRONT PANEL LED INDICATORS ................................................................................................ 4–2
TABLE 5-1 25 PIN ‘D’ TYPE FEMALE................................................................................................................5–1
TABLE 5-2 ALARMS CONNECTOR.....................................................................................................................5–2
TABLE 5-3 REMOTE CONTROL CONNECTOR.................................................................................................5–2
TABLE 5-4 AUXILIARY SERIAL CONNECTOR................................................................................................5–3

CDM-500 Satellite Modem Preface
Rev. 1.3 vii
About this Manual
This manual provides installation and operation information for the Comtech EFData
CDM-500 satellite modem. This is a technical document intended for earth station
engineers, technicians, and operators responsible for the operation and maintenance of
the CDM-500.
Conventions and References
Cautions and Warnings
CAUTION
CAUTION indicates a hazardous situation that, if not avoided, may result in
minor or moderate injury. CAUTION may also be used to indicate other
unsafe practices or risks of property damage.
WARNING
WARNING indicates a potentially hazardous situation that, if not avoided,
could result in death or serious injury.
Metric Conversion
Metric conversion information is located on the inside back cover of this manual. This
information is provided to assist the operator in cross-referencing English to Metric
conversions.
Reporting Comments or Suggestions Concerning this Manual
Comments and suggestions regarding the content and design of this manual will be
appreciated. To submit comments, please contact the Comtech EFData Customer Support
Department.

Preface CDM-500 Satellite Modem
viii Rev. 1.3
IMPORTANT INFORMATION - PLEASE READ
BEFORE INSTALLATION AND USE
SAFETY NOTICES
Electrical Safety
The CDM-500 VSAT Modem has been shown to comply with the following safety
standard:
EN 60950: Safety of Information Technology Equipment, including electrical
business machines
The equipment is rated for operation over the range 100 - 240 volts AC. It has a
maximum power consumption of 25 watts, and draws a maximum of 250 mA.
The user should observe the following instructions:
Fuses
The CDM-500 is fitted with two fuses - one each for line and neutral connections. These
are contained within the body of the IEC power inlet connector, behind a small plastic
flap.
For 230 volt AC operation, use T0.5A, 20mm fuses.
For 115 volt AC operation, use T1A fuses, 20mm fuses.
FOR CONTINUED OPERATOR SAFETY, ALWAYS REPLACE THE FUSES WITH
THE CORRECT TYPE AND RATING.
Environmental
The CDM-500 must not be operated in an environment where the unit is:
• Exposed to extremes of temperature outside the ambient range 0 to 50 C, 0
precipitation, condensation, or humid atmospheres above 95% RH,
• Altitudes (un-pressurised) greater than 2000 metres, excessive dust or vibration,
flammable gases, corrosive or explosive atmospheres.
• Operation in vehicles or other transportable installations which are equipped to
provide a stable environment is permitted. If such vehicles do not provide a stable
environment, safety of the equipment to EN60950 may not be guaranteed.

CDM-500 Satellite Modem Preface
Rev. 1.3 ix
Installation
The installation and connection to the line supply must be made in compliance to local or
national wiring codes and regulations.
The CDM-500 is designed for connection to a power system that has separate earth, line
and neutral conductors. The equipment is not designed for connection to power system
which has no direct connection to earth.
The CDM-500 is shipped with a line inlet cable suitable for use in the country of
operation. If it is necessary to replace this cable, ensure the replacement has an equivalent
specification. Examples of acceptable ratings for the cable include HAR, BASEC and
HOXXX-X.
Examples of acceptable connector ratings include VDE, NF-USE, UL, CSA, OVE,
CEBEC, NEMKO, DEMKO, BS1636A, BSI, SETI, IMQ, KEMA-KEUR and SEV.
Telecommunications Terminal Equipment Directive
In accordance with the Telecommunications Terminal Equipment Directive 91/263/EEC,
this equipment should not be directly connected to the Public Telecommunications
Network.
EMC (Electromagnetic Compatibility)
The CDM-500 VSAT Modem has been demonstrated, by independent testing, to comply
with the following standards:
Emissions: EN 55022 Class B - Limits and methods of measurement of radio
interference characteristics of Information Technology Equipment.
FCC Part 15 Class B
Immunity: EN 50082 Part 1 - Generic immunity standard, Part 1: Domestic,
commercial and light industrial environment.
In order that the Modem continues to comply with these standards, observe the following
instructions:
• Connections to the transmit and receive IF ports (BNC female connectors) should be
made using a good quality coaxial cable – for example RG58/U (50 ohm) or RG59/U
(75 ohm).
• All 'D' type connectors attached to the rear panel must have back-shells which provide
continuous metallic shielding. Cable with a continuous outer shield (either foil or
braid, or both) must be used, and the shield must be bonded to the back-shell.
• The equipment must be operated with its cover on at all times. If it becomes necessary
to remove the cover, the user should ensure that the cover is correctly re-fitted before
normal operation commences.

Preface CDM-500 Satellite Modem
x Rev. 1.3
Warranty Policy
This Comtech EFData product is warranted against defects in material and workmanship
for a period of two years from the date of shipment. During the warranty period, Comtech
EFData will, at its option, repair or replace products that prove to be defective.
For equipment under warranty, the customer is responsible for freight to Comtech
EFData and all related custom, taxes, tariffs, insurance, etc. Comtech EFData is
responsible for the freight charges only for return of the equipment from the factory to
the customer. Comtech EFData will return the equipment by the same method (i.e., Air,
Express, Surface) as the equipment was sent to Comtech EFData.
Limitations of Warranty
The foregoing warranty shall not apply to defects resulting from improper installation or
maintenance, abuse, unauthorized modification, or operation outside of environmental
specifications for the product, or, for damages that occur due to improper repackaging of
equipment for return to Comtech EFData.
No other warranty is expressed or implied. Comtech EFData specifically disclaims the
implied warranties of merchantability and fitness for particular purpose.
Exclusive Remedies
The remedies provided herein are the buyer's sole and exclusive remedies. Comtech
EFData shall not be liable for any direct, indirect, special, incidental, or consequential
damages, whether based on contract, tort, or any other legal theory.
Disclaimer
Comtech EFData has reviewed this manual thoroughly in order that it will be an easy-to-
use guide to your equipment. All statements, technical information, and
recommendations in this manual and in any guides or related documents are believed
reliable, but the accuracy and completeness thereof are not guaranteed or warranted, and
they are not intended to be, nor should they be understood to be, representations or
warranties concerning the products described. Further, Comtech EFData reserves the
right to make changes in the specifications of the products described in this manual at any
time without notice and without obligation to notify any person of such changes.
If you have any questions regarding your equipment or the information in this manual,
please contact the Comtech EFData Customer Support Department.

Rev. 1.3 1–1
1Chapter 1.
INTRODUCTION
1.0 Introduction
The CDM-500 (Figure 1-1) is a very low-cost Closed Network Satellite Modem, intended
for VSAT applications. It offers variable data rates from 2.4 to 512kbps, in BPSK and
QPSK modes. It is extremely compact, being 1U high and 12 inches deep, and consumes
only 18 watts. It has a front panel VFD display and keypad for local configuration and
control, although it can be fully remote-controlled. For 1:1 applications the CDM-500 is
supported by a low-cost external switch, the CRS-100. For Hub applications, the CDM-
500 is supported by a low-cost 1:N switch, the CRS-200. Its fast acquisition time makes
it attractive for both demand-assigned and fixed-assigned SCPC applications.
Figure 1-1. CDM-550 Satellite Modem

Introduction CDM-500 Closed Network Satellite Modem
1–2 Rev. 1.3
The CDM-500 includes, as standard, a universal data interface which eliminates the need
to exchange interface cards for different applications. The interfaces offered include
RS422 (EIA530) DCE, V.35 DCE, synchronous RS232 DCE, and X.21 DTE and DCE.
The internal software is both powerful and flexible, and permits the user to store, and
then retrieve, up to 10 different modem configurations. The unit includes many test
modes and loopbacks for rapid verification of the correct functioning of the unit. Of
particular note is the IF loopback, which permits the user to perform a quick diagnostic
test without having to disturb external cabling. During the loopback, all of the receive
configuration parameters are temporarily changed to match those of the transmit side.
When normal operation is again selected, all of the previous values are restored.
A perennial problem is that of the IF port impedance. Whilst many users select the
universal standard of 50 ohms, there are many users who are still using 75 ohms. In the
past this has presented difficulties for the manufacturer, who has traditionally had to offer
both options. The CDM-500 eliminates this problem, by offering both impedances in the
same unit. The user simply selects from the front panel which impedance he wishes to
use.
In order to facilitate network management, the CDM-500 incorporates EDMAC, an
acronym for Embedded Distant-end Monitor And Control. In this mode, an additional 5%
overhead is combined with the traffic data, which permits M&C information to be added
(transparently to the user), allowing access to the distant-end modem.
This mode does not require any additional cabling at either the local or distant-end
Modems - access to EDMAC is via the standard M&C control port. Full monitor and
control is possible, and importantly, the on/off status of the carrier at the distant-end
carrier can be controlled.
The CDM-500 has been designed as a companion product for the Comtech EFData line
of RF Transceivers. As such, the Modem incorporates an FSK serial link which can be
activated on the Receive IF port, for the purpose of communicating with a Transceiver, if
connected. In this manner, a user may monitor, configure, and control the Transceiver,
using the front panel display and keypad of the Modem. The EDMAC channel may also
be used to convey M&C data to a Transceiver at the distant end of a satellite link, if it is
connected to a CDM-500.

Rev. 1.3 2–1
2Chapter 2.
INSTALLATION
2.0 Unpacking
Inspect shipping containers for damage. If shipping containers are damaged, they should
be kept until the contents of the shipment have been carefully inspected and checked for
normal operation.
Remove the packing list from the outside of the shipping carton. Open the carton and
remove the contents, checking the contents against the packing list. Verify completeness
of the shipment and that the unit functions correctly. If damage is evident, contact the
carrier and Comtech immediately and submit a damage report. Be sure to keep all
shipping materials for the carrier's inspection.
If the unit needs to be returned to Comtech EFData, please use the original shipping
container.
2.1 Mounting
If the CDM-500 is to be mounted in a rack, ensure that there is adequate clearance for
ventilation. The CDM-500 does not include a cooling fan, so care must be taken that too
many units are not mounted on top of each other. The limit is four units, and then a blank
1U panel must be inserted to allow sufficient airflow around the units. In rack systems
where there is high heat dissipation, forced air cooling must be provided by top or bottom
mounted fans or blowers. Under no circumstance should the highest internal rack
temperature be allowed to exceed 50 C.

Installation CDM-500 Closed Network Satellite Modem
2–2 Rev. 1.3
Note that the CDM-500 is very light - under 7 lbs (3.2 kgs), and very short – 12 ins (305
mm). For this reason, it has not been designed to have rack slides mounted to the side of
the chassis. However, Comtech recommends that some method of support within the rack
should be employed, such a rack shelves. If the user is any doubt, please consult the
factory.
2.2 Configuration
There are no internal jumpers to configure, no interface cards to install, and no other
options to install. All configuration is carried out entirely in software. The unit should
first be configured locally, using the front panel keypad and display. The unit will ship
with a default 64 kbps, QPSK, Rate 1/2 configuration. Please refer to the ‘FRONT
PANEL OPERATION’ section for details on how to fully configure the unit for the
desired operating parameters.
The auto-sensing AC power supply does not require any adjustments. Simply plug in the
supplied line cord, and turn on the switch on the rear panel.
2.3 Select Internal IF Loop
Correct operation of the unit may be verified rapidly, without the need for
externally connected equipment. From the top level menu, select TEST, then IF
LOOP (refer to the ‘FRONT PANEL OPERATION’ section) The demod should
synchronize, and the green RECEIVE TRAFFIC LED should illuminate. If the unit
does not pass this test, call the factory for assistance.
2.4 Connect External Cables
Having verified correct operation in IF loop, the user should now enter his desired
configuration, and proceed to connect all external cables. If difficulties are experienced,
please call the factory for assistance.
Please note that the modulator gives an output power level in the range 0 to –20 dBm,
and the demodulator expects to see a signal in the range -30 to -60 dBm.

Rev. 1.3 3–1
3Chapter 3.
FUNCTION
3.0 Functional Description
The CDM-500 has two fundamentally different types of interface - IF and data. The data
interface is a bi-directional path which connects with the customer’s equipment (assumed
to be the DTE) and the modem (assumed to be the DCE). The IF interface provides a bi-
directional link with the satellite via the uplink and downlink equipment.
Transmit data is received by the terrestrial interface where line receivers convert the
clock and data signals to CMOS levels for further processing. A small FIFO follows the
terrestrial interface to facilitate the various clocking and framing options. If framing is
enabled, the transmit clock and data output from the FIFO pass through the framer, where
the EDMAC data is added to the main data. Otherwise, the clock and data are passed
directly to the Forward Error Correction encoder. In the FEC encoder, the data is
differentially encoded, scrambled, and then convolutionally encoded. Following the
encoder, the data is fed to the transmit digital filters, which perform spectral shaping on
the data signals. The resultant I and Q signals are then fed to the QPSK/BPSK modulator.
The carrier is generated by a frequency synthesizer, and the I and Q signals directly
modulate this carrier to produce an IF output signal.
The received IF signal is first translated to a fixed IF frequency, using a frequency
synthesizer. An AGC circuit maintains the composite level within the IF bandwidth
constant over a limited range. Following this, the signal is sampled by a high-speed
(flash) A/D converter. All processing beyond this conversion is purely digital. The signal
is translated down to near zero frequency by a complex mix, and then is processed by a
digital Costas Loop, which performs the functions of Nyquist filtering, carrier recovery,
and bit-timing recovery. The resultant demodulated signal is fed, in soft decision form, to
the Viterbi (FEC) decoder. After decoding, the recovered clock and data pass to the de-
framer (if EDMAC is enabled) where the overhead information is removed.