your location it may be night at the
other location. So, bear this in mind
when you are receiving signals from
the remote location.
When tuning through the bands
— as with any shortwave radio — you
will discover that there are some
audible sounds that do not make
immediate sense. There may be
warbles, buzzes, and whistles that
seem to vary and repeat. The
unconventional sounds you are
hearing are probably data signals.
This is the other world of shortwave
radio; one that does not use
conventional sounds. It is the realm
of audio data transmissions.
We have previously discussed
how to receive data signals with a
low cost shortwave radio (N&V May
2015). Now, the concept takes on a
new dimension since we are using
virtual radios not in our possession.
As astonishing as it seems, many
of these Web based shortwave
receiver data signals can be
processed and decoded using just
your PC and some free decoding
software. Yes, some signals are
encrypted, and can’t be decoded.
Fortunately, there are plenty of
unencrypted data signals around to
keep us busy for a long time.
However, as will be discussed
later on, it does require a special trick
to allow you to pipe the streaming
audio signals from the Web to the
decoding software. In this article, I
will show you how to use these Web
based shortwave receivers to access
data transmissions and to get started
in this exciting hobby.
A Closer Look at
Data transmissions vary in
complexity and contain a wide
variety of information. Some are as
simple as Morse code (CW) or
Radio-teletype (RTTY), while others
are more sophisticated, such as
AMTOR or SITOR which are similar
to RTTY. Several software decoding
packages will be discussed later to
help you get started with these
modes. The good news is that they
are free and can be downloaded
from the Internet. Most of this
application software can also decode
the newer modes.
Some of the popular newer
modes are Binary Phase Shift Keying
(BPSK), Weak Signal Propagation
Reporter (WSPR), and the weak
signal digital modes JT65/9. These
modes — developed by amateur
radio operators — use low power,
complex coding, and allow
communication over great distances.
Text messages are usually conveyed
with these protocols. To convey
images and graphics, commercial
stations use radio-facsimile (FAX),
while amateur stations use slow scan
TV (SSTV) and EasyPal. We will
discuss more about these software
applications later on as well.
One of the things that all of
these modes have in common is that
they are audio modes. That is, the
radio signals are first converted to
audio signals using your radio
receiver. If your receiver is connected
to a PC sound card, the sound can
be piped to your software decoder.
This is usually as easy as selecting
your sound card as input in the
However, if you are receiving the
audio from the Internet, things are
not so simple. Let’s take a look at
how audio is delivered over the
Internet Audio —
Don’t worry; this will not be a
treatise on how the Internet works.
Thankfully, many of the details of
data transfer are hidden from the
user and handled automatically. It is
helpful to understand some concepts,
however. Two major ways data is
conveyed are downloading and
Computerized information (data)
moves efficiently across the Internet
by being broken up into little chunks
known as packets. Each packet is
independently addressed and travels
separately, and different packets can
travel by different routes.
When you download a file in the
traditional way, you’re effectively
asking a server to send you many
packets one after another, and you
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FIGURE 2. Screenshot of Web based receiver.
June 2017 41