Ewave Radio Modem User’s Manual V1.02
Copyright © 2001 by Ewave, Inc.
6
3
Theory of Operation
3.1
Anatomy of an Ewave Radio Modem
The picture below shows one of the two types of Ewave packet radio modems, which are arbitrarily
referred to as Mobile (short flexible black antenna) and Base (longer swiveling chrome antenna). The
“Mobile” or “Base” units are interchangeable -- in any system either or both units can be fixed or portable
(though the Mobile’s short flexible antenna lends itself to portable use). However, it is important to note
that a Mobile unit will not communicate directly with another Mobile and likewise a Base unit will not
communicate directly with another Base. This is a necessary consequence of the fact that the modems are
full-duplex (meaning data may be transmitted and received simultaneously): To allow full-duplex
operation, the Base and Mobile units contain matched pairs of the Ewave RF transceiver module which are
optimized to transmit on a different range of frequencies (e.g., the Base units transmit on 926-928 MHz
while the Mobile units transmit on 902-904 MHz. The exact frequencies for each channel are listed in the
appendix.)
Note that it is possible to implement various “multi-drop” or “multi-node networks” schemes with the
Ewave Radio Modems – a single modem of one type communicating with several of the opposite type. For
example, this can be done through on-the-fly control of Transmit Power.
The picture at left shows a Mobile Ewave Radio
Modem unit.
The DB9 connector supplies standard RS232 or
RS422 signals.
5V 140mA regulated power may also be supplied
via the DB9, or the modem may be powered by
unregulated DC (7.2-10V, 140mA) supplied via
the side plug. If this is done, regulated 5V will be
available via the DB9 and may be used to power
an external 5 Volt device.
