RAD Data comm 146 - Manual

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146
RAD Data Communications 2006 Catalog
Miniature short range modems offer the
same communications functions as AC-
powered 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-to-
point 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. Interface-
powered 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?)
A Quick Reference Guide on pages 158-159
will help you select the most suitable
modem for your application.
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 Modems
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