TM 11-5820-803-12
CHAPTER 1
INTRODUCTION
Section I. GENERAL
1-1.
Scope.
Report (DISREP) (SF 361) as prescribed in AR
This manual describes Modem, Digital Data MD-921/G,
5538/NAVSUPINST
4610.33C/AFR
75-18/MCO
hereinafter referred to as the PSK modem (fig. 1-1). It
P4610.19D/DLAR 4500.15.
includes installation, operation, maintenance, and
troubleshooting for operator/ organizational maintenance.
1-4.
Reporting
Equipment
Improvement
Recommendation (EIR)
contains the maintenance allocation chart.
If your equipment needs improvement, let us know. Send
us an EIR. You the user, are the only one who can tell
1-2.
Consolidated Index of Army Publications and
us what you don't like about your equipment. Let us know
Blank Forms
why you don't like the design. Tell us why a procedure is
Refer to the latest issue of DA Pam 310-1 to determine
hard to perform. Put it on an SF 368 (Quality Deficiency
whether there are new editions, changes or additional
Report).
Mail it to Commander, US Army
publications pertaining to the equipment.
Communications-Electronics Command and
Fort
Monmouth, ATTN: AMSEL-ME-MP, Fort Monmouth,
1-3.
Maintenance Forms, Records, and Reports
New Jersey 07703-5007. We'll send you a reply.
a. Reports of Maintenance and Unsatisfactory
Equipment Department of the Army forms and
1-5.
Administrative Storage
procedures used for equipment maintenance will be
a. Administrative storage of equipment issued to
those prescribed by DA Pam 738-750 as contained in the
and used by Army activities will have preventive
Maintenance Management Update. Air Force personnel
maintenance performed in accordance with the PMCS
will use AFR 66-1 for maintenance reporting and TO-00-
charts before storing. When removing the equipment
35D54 for unsatisfactory equipment reporting. Navy
from administrative storage, the PMCS should be
personnel will report maintenance performed a utilizing
performed
to assure
operational readiness.
the Maintenance Data Collection Subsystem a (MDCS)
Disassembly and repacking equipment for shipment or
IAW OPNAVINST 4790.2 Vol 3 and unsatisfactory
limited storage is covered in SB 38-100.
material/conditions (UR submissions) IAW OPNAVINST
b. COMSEC equipment must be removed before
4790.2 Vol 2, chapter 17. s
storage, and turned in to the COMSEC
account
b. Report of Packaging and Handling Deficiencies.
custodian.
Fill out and forward SF 364 (Report of Discrepancy
(ROD)) as prescribed in AR 735-11-2/DLAR
1-5.1. Destruction of Army Electronics Materiel
4140.55/NAVMATINST 4355.73A AFR 400-54/ MCO
Destruction of Army electronics materiel to prevent
4430.3F.
enemy use shall be in accordance with TM 750-244-2.
c. Discrepancy in Shipment Report (DISREP) (SF
COMSEC equipment and keying information have first
361). Fill out and forward Discrepancy in Shipment
priority.
Section II. DESCRIPTION AND DATA
1-6. Purpose and Use
1-7. Description
The PSK modem provides a means of interfacing digital
The PSK modem (figs. 1-3 and 1-4) is designed for rack
data over the Defense Satellite Communications System
mounting in a standard 19-inch equipment rack. It is 12
(DSCS). The modem converts between the baseband
1/4 inches high and 22 inches deep. Operating controls
data signals required by a digital user and the modulated
are located on the front panel and under the top cover
70 MHz signals required by a satellite ground terminal
behind the front panel. Indicators and test jacks are also
located on the front panel. Two fans and the external
receive sections which
provide the user with the
interface connectors are located on the rear of the
capability of full duplex digital communication. The
chassis. The chassis contains two card file assemblies,
modem will process data at any rate between 19.200
each of which has two files capable of accepting 24
kb/s and 9.9999 Mb/s. Self-test, link test, and on-line
cards. One assembly is accessible through the top cover
fault monitoring functions are built into the modem.
and the other through the bottom cover. The top
Internal or external error-correcting coders/decoders can
assembly, A2A1, contains 17 printed circuit cards in the
)be employed if required to improve the quality of the
Al file, 19 cards in the A2 file. The bottom assembly,
communications.
A2A2, contains 20 cards in the A1 file and 9 cards in the
A2 file. Located on
Change 2 1-1
