RAD Data comm 146 User Manual

Miniature Modems

Miniature short range modems
offer a simple, low cost and highly
reliable method to connect digital
devices in a local, campus or
metropolitan environment. They
also offer very easy installation
since in many cases they do not
require AC power, but derive their
power from the interface signals.

Miniature short range modems offer the
same communications functions as AC­powered modems but with fewer features,
such as limited diagnostics capability and no
BER tests. Usually they operate over shorter
distances at lower rates (normally up to

19.2 kbps). However, certain modems can
operate at data rates up to 115.2 kbps in
async transmission and up to 128 kbps in
sync transmission. Like AC-powered
modems, miniature modems are designed
to overcome distance limitations of standard
data communications interfaces such as
V.24/RS-232. They also overcome noisy
environments and provide ground isolation.

Miniature short range modems connect
computers, terminals, bridges/routers and
similar data communications devices inside
buildings, campuses or within city
boundaries. They support simple point-to­point communications as well as complex
multipoint campus-wide systems. They also
support flow control when connected to a
printer or a multiplexer.

Typical communications problems, such as
distance limitations and noise, are overcome
by using special signal modulation and line
equalization techniques that allow for
error-free transmission over longer
distances. RAD miniature modems have
transformers to isolate the equipment from
the line and ensure safety. The transformers
are rated at over 1,500 VRMS and are
approved by carriers worldwide for
connection to their lines.

What is the difference between
interface-powered and AC-powered
modems?

Interface-powered and AC-powered
modems perform the same basic
communications functions. Interface­powered modems incorporate innovative
VLSI and hybrid circuitry that enable them to
consume very little power. These modems
draw power from the interface signals
without loading the adjacent equipment or
interfering with normal operation. For
computers that do not support control
signals, there are special models that derive
their power solely from the data signals.

How do you select the right modem for
your application?

Several factors should be considered when
selecting a modem:

• Computer/DTE interface: V.24/RS-232,
V.35, etc.

• Communication method: sync, async or
both

• Data rate

• Distance

• Media: twisted pair, coax, fiber

• Point-to-point or multipoint application

• Control signals (does the application
require transmission of data only, or also
transmission of one or more control
signals?)

• Environment (is the environment noisy?)

146

A Quick Reference Guide on pages 158-159
will help you select the most suitable
modem for your application.

RAD Data Communications 2006 Catalog

MINIATURE SHORT RANGE MODEMS

RS-423/422
converter

4-wire, async

Fiber optic

Fiber optic

4-wire

Elastic buffer

Multidrop
sync/async

56/64 kbps

CMN-16

Elastic
buffer

RS-422

19.2 kbps

Fiber optic

Fiber optic

FOM-6A

SRM-8

SRM-8

SRM-8

High
speed

SRM-8H

IBM 3174

SRM-6AC

FOM-5A

FOM-8

CMN-16

Compact Modem Nest

12

MINIATURE SHORT RANGE MODEMS

• High density modem rack

• 2U high

• Accommodates copper and fiber optic

modems

• Indicator LEDs on each card

• V.54 diagnostics available with several

cards

• Redundant power supply

Visit www.rad.com for latest product updates

The CMN-16 compact modem nest is a space-saving
rack that houses up to 16 short range modem cards.
Most of the cards carry two modems, doubling the
capacity of the nest to up to 32 modems. The nest
provides an inexpensive solution to central site racking
of short range modems. In addition to short range
modems, the nest supports interface converters, fiber
optic modems and elastic buffers.

The CMN-16 is compatible with the SRM short range
modem family and has the added capability of
displaying activity on the interface signals.

The following cards are available:

CMN-C6A – dual async short range modem
card, compatible with SRM-5A, SRM-6A,
SRM-3A

CMN-C6AC – dual async multipoint short
range modem card, compatible with
SRM-5AC, SRM-6AC

CMN-C6S – sync short range modem card,
compatible with SRM-5S, SRM-6S

CMN-C6SC – sync multipoint short range
modem card, compatible with SRM-5SC,
SRM-6SC

CMN-C6TX – dual async 2 -wire short range
modem card, compatible with SRM-5TX

CMN-C8 – sync/async short range modem
card with V.54 loops, compatible with
SRM-8, ASM-10/8

CMN-C8H – sync/async high speed short
range modem card with V.54 loops,
compatible with SRM-8H

CMN-CF6A – dual async fiber optic short
range modem card, compatible with
FOM-5A, FOM-6A

CMN-CF8 – sync/async fiber optic modem
card with V.54 loops, compatible with
FOM- 8

CMN-C11 – async short range modem card
with V.54 loops, compatible with ASM-11,
and with ASM-10/8 and SRM-8 in async
mode

CMN-CEB – elastic buffer for connecting
two independently clocked DCEs

CMN-C423/422 – interface converter from
RS-423/V.10 to RS-422/V.11

Several plug-in power supplies are available
for 115/230 VAC and –48 VDC operation.
The card nest can be supplied with two
totally independent plug-in power supply
units, providing redundancy and automatic
backup. A standalone 115/230 VAC high
power version supports two card nests via
cable and card connection.

The CMN-16 is available as a 19" rack
mount enclosure and is 2U (3.5") high.

RAD Data Communications 2006 Catalog

147

MINIATURE SHORT RANGE MODEMS

SRM-31S

128 kbps

2-wire

8km

(5 miles)

LRS-24

ASMi-31-2C

Digital

Network

DTE

SRM-8H SRM-8H

IBM 37X5

56/64 kbps

4-wire

IBM 3174

SRM-31S

Miniature Multirate 2-Wire Modem

• Full duplex transmission over 2 wires in

synchronous transmission

• Data rates up to 128 kbps

• Transmission range up to 8 km (5 miles),

independent of data rate

• Supports IDSL technology (ISDN, U

interface)

• Works opposite the ASMi-31 modem,

including remote control and monitoring,
and LRS-24 modem rack (ASMi-31-2C)

Visit www.rad.com for latest product updates

The SRM-31S miniature synchronous
modem operates full duplex over a single
pair of wires. It supports data rates from

1.2 kbps to 128 kbps. The transmission
range is up to 8 km (5 miles) over 24 AWG
cable, independent of the data rate.

IDSL technology (ISDN, U interface) provides
extended range and efficient transmission
over a single copper pair.

The SRM-31 can operate opposite the
ASMi-31 modem, supporting remote control

and monitoring. When the ASMi-31 is a card
in the LRS-24 rack, the SNMP central
management station can perform control
and monitoring of the remote SRM-31.

Power is provided by a wall-mounted power
supply that is supplied with the product.

End-to-end signaling is available with no
interference to data transmission. The user
can select between RTS/DCD and DSR/DTR
end-to-end signaling options.

SRM-8H

High Speed Short Range Modem

148

• Selectable sync or async operation

• V.54 local and remote diagnostics

• Full or half duplex operation over 4 wires

• Selectable data rates: 56 or 64 kbps

• Range up to 4.5 km (2.8 miles) for 24 AWG

• Controlled or continuous carrier

• Four interfaces: RS-232/V.24, V.35, X.21, RS-530

• Four LED indicators

• Powered via wall-mount power supply

• Line connector options: terminal block,

RJ-12 and RJ-45

Visit www.rad.com for latest product updates

RAD Data Communications 2006 Catalog

The SRM-8H is a high speed short range
modem operating full duplex over twisted
pair, unconditioned telephone lines. It has
an extended range of 4.5 km (2.8 miles) for
24 AWG at data rates of 56 or 64 kbps.

The SRM-8H has diagnostic capabilities
complying with ITU V.54 standard. Two loops
are available: local analog loop and remote
digital loop.

The modem’s carrier can be strapped for
either continuous or switched operation,
controlled by the RTS signal, for passing
control signals.

Transmit timing can be selected for internal,
external or loopback clock. Four LED
indicators monitor Transmit Data, Carrier
Detect, Test and Power.

Four interface models are available:
RS-232/V.24, V.35, X.21, and RS-530.

Power is provided by a standard wall­mounted power supply. Connection of
modems to the line is usually via a 5-screw
terminal block. Other connectors available
are RJ-12 and RJ-45.

The modem is also available as a card
version for mounting in a 19" rack (see the
CMN-16 nest, card CMN-C8H).

Approximate Range (at 56/64 kbps)

Gauge 19 AWG 24 AWG 26 AWG

(0.9 mm) (0.5 mm) (0.4 mm)

Range 10 km 4.5 km 3.2 km

(6.0 miles) (2.8 miles) (2.0 miles)