This unusual radio can be used to receive conventional amplitude modulation (AM) and frequency modulated (FM) stations, as well as more specialized modes such as narrow band FM (NFM), single-side band (SSB), continuous wave
(CW), and other signals. Its performance — while good — is
slightly below the best shortwave listening (SWL) receivers
or ham radios. However, we will show you how to improve
its performance substantially with tunable filters.
As it stands, it does a creditable job in many situations
and has features that many other radios do not — like
digital signal processing, spectrum analysis, and a waterfall
display. As an added bonus, you will be able to receive
frequencies from 24-1766 MHz in case you tire of the
classic shortwave frequencies.
In today’s jargon, this receiver would be called a
software-defined radio (SDR) — a concept made popular
by the military. Typically, in an SDR receiver, an analog-to-digital conversion (ADC) is made on the RF signal, and the
rest of the functions of a classic analog receiver are
performed on the digital signals in software. These
functions include tuning, filtering, and demodulation.
Using software to replace hardware allows more
versatility, provides more functions, and reduces hardware
For this design, we will use a simple RF converter and
a small inexpensive commercial digital TV module to
provide the up-front hardware. The rest of the functions
will be done on the computer.
So, if you want to explore the world of shortwave
radio and learn more about this technology, read on and
definitely consider building your own software-defined
Software-Defined SW Receiver
Figure 1 is a block diagram of our shortwave SDR
receiver. Starting from the antenna, there is an RF
converter/mixer block. The purpose of this block is to
perform frequency up-conversion of the shortwave signals.
This is necessary because the next block requires RF
signals above 24 MHz. Therefore, a simple up-conversion
of the signals is performed using a mixer. Also in this block
are some analog filters to prevent strong AM and FM
signals from overloading the mixer and causing
The next block is a digital TV tuner — an amazing
device that does most of the work. It is connected to the
RF up-converter with a short coaxial cable to its antenna
terminal. In this device, analog signals from the up-converter are tuned, changed to digital signals, and
conveyed via USB to the last block.
The final block is your home PC which performs all
the necessary digital signal processing. It should be
40 July 2015
An Ultra Modern
A simple circuit, a USB TV tuner, your
computer, and some powerful software
combine to make an amazing software defined
By George R. Steber