extension cable may be used to move the RTL farther
away from the computer.
First of all, do not use any of the software that came
with your RTL device. It was designed for a different
application. For our radio, the RTL stick requires a special
USB driver and a graphical radio interface. You will need
to install Zadig for bulk interface drivers and then SDR#
for the radio interface. Once Zadig is run, you will have a
new USB driver named “Bulk-In, Interface (Interface 0).”
That is what the RTL device uses.
After you install SDR#, you will be able to select this
driver to use with your radio. Also note that — depending
on your PC operating system — you may need Microsoft’s
Net 3. 5 for the installation to work.
The software installation discussed earlier is too
detailed to present here. The following websites can take
you through the procedure. Perhaps the best site that
covers the entire installation is
www.rtl-sdr.com/rtl-sdr-quick-start-guide. Other sites to check are
The installation may seem a bit daunting when you are
just starting out, but remember, once you get it working it
will be well worth the effort.
A screenshot of SDR# tuned to WWV is shown in
Figure 7. It’s interesting to see atmospheric fading in the
waterfall plot. Running SDR# is like having
a radio lab at your disposal. More details
on its operation can be found at
Now, let’s take a look at some of the
screen buttons. In the upper left corner is
the Play button — which obviously starts
the program. What is not obvious is that
some settings cannot be changed while it is
running. So, if you cannot set something,
make sure the program is stopped. The first
thing you should do is select the USB driver
you installed by pressing the down arrow
located next to the Play button. Choose
RTL-SDR/USB from the available options.
Next, click Configure. Choose a sample
rate of 1.024 MSPS and Quadrature
sampling. Leave the other boxes blank.
Notice that there is a slider to select the RF
gain. Set it to about 14. 4 dB. It can be
changed later if it’s too low. There is
another box at the bottom that allows
correction for the crystal frequency inside
the RTL. We will discuss that later.
Now, look below the Play button.
There are numerous buttons for selecting NFM, AM, and
so forth. In this screen area is a box labeled Shift. Click
this box and enter: 24,000,000. Notice the ‘minus’ sign.
This number corresponds to the crystal frequency in the
up-converter and will provide the first rough correction —
it enables SDR# to read out the RF SW frequency directly.
Now, move down to the Audio section. The
Samplerate and Input boxes should be grayed out. This is
because data is being sent via USB not audio. In the
Output box, select the sound card that you are using. It
will produce the sound you will hear.
Let all of the other settings in SDR# be at their default
for now. You will have lots of fun experimenting with them
later on. Connect a long wire antenna and ground
counterpoise. Make them as long as possible — 25 feet or
more. With any luck, you should now have a functioning
Three automatic gain controls (AGC) are available.
The ones in the Configure box do not work well. The AGC
on the main screen works well on strong stations. For
weak stations, leaving AGC off and manually adjusting the
RF gain may work best.
Other SDR# settings are usually a matter of
preference, but here are some guidelines. Generally, a
moderate value of Zoom should be used unless you are
calibrating the radio. This makes it easier to click on a
peak to select a station. Use a small number for FFT —
typically 4096 to get good computer performance. Use a
bandwidth that is appropriate for the signal being
monitored: CW 800 Hz; SSB 2. 8 kHz; and AM 10 kHz. A
44 July 2015
FIGURE 6. Breadboard of tunable filter shortwave radio.