built-in noise suppression to prevent computer noise
from getting to the radio. To connect the audio, look
for the audio-out jack on the radio.
Most radios have a provision for connecting to
headphones or an external speaker. For the DE1103,
the connection is easy as there is a line-out jack on
the side of the radio. Finally, you need to know how
to adjust the line-input level in the sound card
recording section of your PC.
Getting to Know Your Receiver
Spend some time getting acquainted with your
receiver’s operating controls. There will generally be
controls to select the audio bandwidth, adjust the
frequency, select the SSB mode, and adjust the BFO
frequency. For the DE1130, the narrow-wide switch
selects either 4 kHz or 6 kHz wide audio. In most cases,
use the wide setting as powerful audio filters in the
software will filter the noise. To select the desired radio
frequency in kHz, enter the desired digits, press BAND+,
and select SSB.
With this radio — as with many radios — you can only
select the frequency to the nearest kHz since only the five
most significant digits can be entered. That’s okay for
receiving AM stations, but for receiving SSB voice signals
smaller frequency adjustments need to be made. This is
done via the BFO knob on the side of the unit.
Understanding the BFO
The BFO effectively provides variable adjustment of
about 1.5 kHz above and below the dial frequency as
seen in Figure 4. It is usually un-calibrated, however. In
other words, the last — or lesser — three digits of the true
dial frequency setting are unknown. More frequency
precision needed for data transmissions can be achieved
by calibrating the BFO.
Typically, seven digits of frequency are needed to
locate specific radio bands and for accurate signal
reporting. Thus, we need to determine the true RF
receiving frequency of the radio when using SSB and
the BFO together.
For my DE1103, the BFO knob allows frequency
adjustment of plus 1,600 Hz to minus 1,300 Hz from
the displayed dial frequency. The maximum BFO
frequency (1,600 Hz) is attained with the BFO knob
set fully counter-clockwise (CCW). Turning the knob
CW from the fully CCW position causes a decrease
in the BFO frequency, gradually reducing it to 0 Hz
and then further to -1,300 Hz.
Here is an example of how the BFO affects the
true radio dial. Suppose the displayed radio dial is
14,020 kHz and the BFO is set to +755 Hz. Adding
the two, the true dial setting would be 14020.755
kHz ( 14.020755 MHz). In this example, we now
have eight digits of frequency. In practice, the last
digit will not be known to high accuracy. However, it will
be good enough to get us to the right shortwave band
segments — usually within 10 Hz.
If the BFO knob was calibrated in frequency, this
would be the end of the story. Most BFOs — particularly in
low cost radios like the DE1103 — are not. Another
problem is that the BFO frequency will change a small
amount with dial frequency. The good news is that we can
easily overcome these problems using an audio spectrum
analyzer on our PC and two standard candle radio stations
separated widely in frequency.
These standard candle radio stations can be an AM
radio station near 1,000 kHz and a shortwave station like
WWV at 10 MHz. WWV has a very accurate frequency,
and AM stations are required to be within 20 Hz of their
assigned frequency. This allows us to perform a calibration
for our radio’s BFO. It is easy and fun. Here’s how to do it.
Calibrating Your BFO on SSB
First, get an audio spectrum analyzer (SA) running on
your PC. A good choice is the free program
May 2015 59
FIGURE 5. SpectrumView audio spectrum analyzer.