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product review
WM232-UHF
Short range,
high-performance
wireless modem
The applications for radio as a medium to connect devices is virtually
unlimited. Some applications demand wireless connection, due to
difficult access or for mobility reasons. Others, such as metering and data
acquisition systems can benefit greatly from wireless technology. No
network cabling and no direct access to equipment is needed, reducing
costs right from the installation stage and beyond.
T
he WM232-UHF, an Australiandesigned and manufactured radio modem, is a low-cost, plug’n’-play connectivity solution for
devices that communicate via serial
links. It supports on-air data rates of up
to 14.4kbps and features data encryp32 Silicon Chip
tion, error checking and acknowledged
data transfer.
The basics
The modem is housed in a small
ABS plastic case, measuring about
103mm (L) x 62mm (W) x 24mm
(D). Antenna hookup is via an SMA
connector that protrudes through one
end of the case. A tiny (60mm) helical
stubby antenna can be mounted directly onto the SMA connector, making a
very tidy little package.
Power for the unit can be provided
www.siliconchip.com.au
by Peter Smith
Fig.1: Point to Point mode allows simple, transparent connections
between any two devices with RS232 ports.
by either an internal 9V PP3 battery or
around 500m line-of-sight. Of course,
dressing system, composed of “unit”
an external 7-15V DC source. A 9V DC
you could also fit a more elaborate
and “site” addresses.
plugpack was supplied with our evalu“gain” antenna for much greater range,
Up to 16 pairs of modems can operation unit. The average current drawn
but that wouldn’t be legal, now would
ate within a single site address, with
during transmit/receive is quoted at
it?
up to eight possible site addresses.
40mA, falling to 15mA when idle.
This corresponds to a maximum of 127
Wireless simplicity
This means that an external power
possible point-to-point links.
source will be necessary for most
In their simplest configuration, two
Site addressing effectively partiapplications. In power-down mode,
WM232-UHF modems can function as
tions groups of modems for repeating
consumption drops to a more respecta reliable two-way wireless link.
purposes. Any WM232-UHF can
able 400µA.
operate as a dedicated repeater unit.
Apart from a certain amount of
Connection to the modem is made
latency in the data exchange, the
Up to three repeaters can be used
via a 9-pin female ‘D’ connector.
modems appear transparent to the
within a network to extend the opPin assignments conform to the PC
connected devices, functioning just
erating range. A repeater retransmits
modem (DCE) standard, so for conas they would if they were hard-wired
any data it receives with the same
nection to a PC (DTE) serial port all
together. This mode of operation is
site address, allowing very flexible
that’s required is a 9-way pin to pin
called “Point-to-Point”.
networks to be constructed.
cable (supplied).
For more demanding applications,
It is important to note that effecThe unit operates in the 433.920MHz
multiple pairs of modems can operate
tive data throughput for any pair in a
LIPD (license-free) band, with transmit
within the same air space.
network will decrease as the network
power limited to
is expanded, as the available airtime
This is achieved with a two-tier ad10mW (ERP) to satalways remains constant.
isfy the regulatory
An LBT (Listen
requirements.
Before Transmit)
√ Easy configuration via
PC, laptop or PDA
Receiver sen scheme is employed
√
Point to point or multip
sitivity is quoted
to
minimise the inoint network capability
at -100dBm for a √ Repeater support
terference that ocfor increased range
1ppm BER (Bit Er- √ Se
curs when multiple
rial port speeds of 600
to 115200 baud
ror Rate), giving
modems attempt to
a range of about √ On-air data speeds of 600 to 14400
transmit simultanebaud
300m line-of-sight √ On-air data encryption
ously.
and error checking
and 50m indoors √ Diagnos
tic “Radar” and “Ping”
More about netfunctions
with the helical
√ DTR-controlled “slee
stubby fitted.
p” mode
working
A n o p t i o n - √ Internal 9V battery or externa
A common requirel DC plugpack
a l c o a x - f e d , √ Range of up to
ment
within a wire500m with coax-fed ha
lf-wave antenna
ground-inde- √
less network is to
CE & Australian C-Tic
k approval for use on
pendent halfbe able to monitor
licence-free UHF Band
wave dipole exand control multiple
tends the range to
nodes from a central
Features
www.siliconchip.com.au
February 2003 33
product review (continued): Telelink Communications WM232-UHF
Fig.2: before data exchange can occur in Point-to-Multipoint
mode, the host first programs the desired slave address into
the master modem.
location. This is the purpose of the
“Acknowledged-Point-to- Multipoint”
mode, where a single modem is configured as the master and all other
modems as slaves.
Each slave is assigned a unique
address, using the same addressing
scheme employed in Point-to-Point
mode.
In order to communicate with a
particular slave modem, the host
must first program the desired slave
address into the master modem. In
Acknowledged-Point-to-Multipoint,
the master modem must initiate a link
with a slave before data transfer to or
from that slave can occur.
By contrast, “MultiMaster” mode
allows up to 15 slave modems to initiate connection with a single master
unit. In this mode, data transfers must
be kept as short as possible to prevent
“hogging” of available airtime.
Design your own network
If none of the above modes suit
34 Silicon Chip
your requirements, then it is possible
to design your own network from the
ground up using “Broadcast Multi-drop” mode.
In this mode, all aspects of network
management, including routing, node
addressing and error recovery, are
assumed to be host-controlled.
Data sent to a modem over its RS232
link is transmitted (broadcast) to all
modems within range.
Receiving modems simply decode
the data and pass it on to their hosts.
Configuration
Modem configuration is accessible,
strangely enough, via configuration
mode. A PC, laptop, or PDA with
an RS232 port and suitable terminal
software (such as HyperTerminal) are
required for the job.
Normally, modems automatically
enter data transfer mode at power up.
To exit data transfer mode and enter
Fig.3: any modem can function as a dedicated repeater. Up to three
repeaters can be added to a network, greatly extending the operating range.
www.siliconchip.com.au
short range wireless modems
configuration mode, it’s just a matter
of sending an “escape” sequence from
the terminal program. The factory
default sequence is three consecutive
“+” characters.
Typing “help” at the configurator
prompt displays all possible commands, whereas “list” displays current
settings (see Figs. 4 & 5). A variety of
useful commands allows mode and
address selection and fine-tuning of
network parameters.
It’s also possible to modify most of
these settings remotely, from a second
modem via a wireless link. Of course,
this feature can be disabled for security
purposes if so desired.
Link testing
Two diagnostic commands have also
been included to aid network setup
and testing.
The “ping” command looks for a
modem within range with the specified address and returns its status.
This is a useful “go-no go” test and
it allows verification of which unit
addresses are in use.
The “radar” command allows link
range and reliability to be quickly
determined. This mandatory feature
will help to eliminate most of the
guesswork from a simple network
installation.
Impressions
Setting up a simple, reliable wireless network with these modems
should be a painless exercise.
And if you have something more
elaborate in mind, the WM232-UHF
can probably handle that too.
Getting more information
Fig.4: configuring the WM232-UHF is dead easy. Here, we’ve used the “list”
command to show all configurable parameters.
The WM232-UHF Wireless Modem
is manufactured and sold in Australia
by Telelink Communications, phone
(07) 4934 0413 or email sales<at>telelink
.com.au
You can reach them on the ’net at
http://www.radiotelemetry.co.uk/ SC
WM232-UHF Modem and
Accessories Prices (inc. GST)
WM232-UHF Modem:......$361.90
WM232-PSU Power
Pack..................................$ 27.50
ANT-UHF-H SMA Helical
Antenna.............................$ 26.40
ANT-UHF-Q SMA 1/4 Wave
Antenna.............................$ 28.60
ANT-UHF-D 3dB Industrial
Dipole................................$ 42.90
Fig.5: the “ping” command is a handy “go-no go” test and allows quick
verification of modem addresses.
www.siliconchip.com.au
A PC Board only version of the
WM232-UHF is available for
OEM’s. (prices on application)
February 2003 35
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