WSPR is that “receptions” (called spots) can be
automatically downloaded to a central database
WSPRnet.org) with results shown on a large map of the
world (see Figure 1). A flag will appear on the map to
show your location and which stations you have received.
Hence, exact transmitter locations can be determined and
distances, headings, and other information reported. The
world map can be zoomed to learn more about the
geography and radio path found. Particularly thrilling for
younger children is this reporting phase as they feel a
sense of participation.
More details about this project (including how to
obtain ready-to-go WSPR receivers, lesson plans for
teachers, and more) are available at http://
stellarwspr.com. WSPR signals are in the amateur radio
part of the spectrum and transmitters will require a license
in most jurisdictions. Happily, many WSPR transmitters are
now operating around the globe to provide interesting
“catches” for the kids.
Band Dial Freq.
FIGURE 2. WSPR radio bands; center frequencies,
bandwidth 200 Hz.
Why Do We Need WSPR?
We know from our high school physics class that
when a transmitter signal moves down a wire to an
antenna that part of it is launched into space as an
electromagnetic (EM) wave. This energy propagates
through space in various directions dependent on many
factors, like the antenna size and orientation. All kinds of
things can happen to the signal after it is launched. It can
be refracted and polarized, for example. For
communication, another antenna some distance away
from the transmitter can intercept part of the signal and
receive a message if one is contained in the signal. For
example, Morse code is sent by turning the signal on and
off (modulating it). Of course, for modern radio
communications more advanced modulation methods are
used. In an ideal universe, the EM wave would propagate
forever and still be able to be demodulated perfectly at
almost any distance with just the tiniest amount of signal
available. However, in our real world there is another
factor. In addition to the things mentioned above, we
need to consider the ramifications of electrical noise.
As the EM wave propagates, it spreads out in space
and therefore diminishes in strength in any given direction.
Simply stated, it gets weaker. To add to the problem, the
ionosphere — which carries much of the high frequency
signals — also is continuously changing, causing
propagation variations like fading. Noise, on the other
hand, is all around our real universe
being generated from all kinds of
things like appliances, radar, and
natural phenomenon like lightning.
The noise level continuously fluctuates
and causes interference to our signal.
To partially deal with the noise
and also to provide additional features,
various modulation techniques have
been developed. Two classic ones you
are probably familiar with are AM
(amplitude modulation) and FM (frequency modulation).
Some modulation methods are better than others at
dealing with noise, but they all get into trouble when the
signal strength approaches the noise level.
WSPR was conceived and put into operation by Joe
Taylor (K1JT), an amateur radio operator (Professor of
Physics at Princeton) and fellow amateur Bruce Walker
FIGURE 3. Typical sound card hookup.
January 2012 45