OPENCOMMUNICATION
THE LATEST IN NETWORKING AND WIRELESS TECHNOLOGIES
■ BY LOUIS E. FRENZEL W5LEF
EXPERIMENTING WITH
COMMERCIAL WIRELESS
MODULES
Wireless everything. That is what I am seeing more and more. Practically
every electronic product these days has some kind of wireless component or
function to it. That’s why it makes sense to learn more about wireless. As you
are experimenting with electronic products, you may discover some devices
you want to imbue with wireless capability.
Adding wireless functionality is easy these days. Transmitter, receiver, and transceiver chips are cheap
and plentiful. Plus, these chips are incorporated into
complete modules you can buy ready to use. Just add a
battery, antenna, and some inputs or outputs. Recently, I
was searching for some inexpensive modules to use in a
college course lab as demos of basic wireless techniques. I
found several, but I ended up with some products from
Linx Technologies ( www.linxtechnologies.com). This
company has a wide range of chips, modules, and
accessories that use low power, short range wireless in the
ISM (industrial-scientific-medical) bands from about 300
MHz to 2. 4 GHz. I chose the 900 MHz products.
Anyway, here is the result of my initial experimentation
with these modules. Hopefully, this will encourage you to
do some wireless experimentation yourself.
SOME WIRELESS BASICS
14 June 2010
Most short-range wireless uses the FCC (Federal
Communications Commission) designated license-free ISM
bands. Some typical frequencies are 315 MHz, 433 MHz,
902-928 MHz, and 2. 4 GHz. You can buy ready to use
chips or modules for any of these bands. The 315 and 433
MHz frequencies are widely used in things like garage
door openers and remote temperature gauges. The 2. 4
GHz band is used for everything like Wi-Fi, Bluetooth,
ZigBee, cordless telephones, and even your microwave
oven. I decided not to use that popular band. Instead, I
went for the 902-928 MHz products. These offer good
range and the antennas are short. Furthermore, this band
does not have as much interference or suffer the effects of
multipath fading that is common on the 2. 4 GHz
microwave band.
Path loss in dB = 37 + 20 log f + 20 log d
The frequency f is in MHz and the range or distance
is in miles. If the range is in feet, divide the number of feet
by 5,280 to get miles. You can also use this formula:
Path loss in dB = 20 log (4π/λ) + 20 log d
Here the wavelength is in meters and the distance d is
in meters.
