80 LXF260 March 2020 http://www.linuxformat.comTUTORIALS Process radio signals
In the image on page 78, the left SDR dongle is housed
in a metal case, and the right dongle is plastic. The metal
acts as a heat sink for the electronic components.
Considering the ADC work the unit is performing there’s
a chance the device will generate heat.
Using a $10 SDR to receive the ‘must have’ critical
weather broadcast is not a good design idea.on a desired frequency. If a weak signal is what you are
after, wideband antennas are not ideal.
Devices will have specifications on the different
features the device supports. Inexpensive SDR
dongles lack some of the technology that increases
performance and provides stability. An example of this
is temperature stabilisation circuitry.Under the receiver control tab there is a
gain control (1) to adjust the amplification
of the signal received. (2) is the audio gain
control for the application. The small black
screen is the audio signal frequency
displayed in real time. This audio gain in
the application is in addition to what your
PC provides. Note: if your PC’s gain is set
to maximum and the app’s gain control is
at the minimum you won’t hear any audio.
Under receiver options tab, (3) is the local
broadcast frequency. (4) Mode is the
type of modulation, in our example FM.
Under the FFT settings tab, (5) divides
the far-left screen between signal screen
(black portion) and the waterfall screen
(blue/yellow mix).
On the main menu bar is a button to get
the application running. You may berequired to establish what device the
application is going to use. Ensure Realtek
RTL2838UHIDIR is the selected device.
(A) displays the broadcast frequency.
(B) is the captured signal. (C) is the
waterfall screen that shows the signal over
time–waterfall means the signal falls off
the bottom of the screen. (D) is the
received signal displayed in yellow. Notice
other yellow tracings for other signals.
The gain control (1) impacts the status
of both (B) and (C/D). If you increase the
gain of a receiver, you are amplifying what
is received. This includes the signal you
want, (B/D) but it also includes all the
other signals, which is why the screen
has more yellow than blue on it. Increase
the gain and you are amplifying noise
along with the signal.Now set up the second application. Turn
off Gqrx before starting. Select Menu >
Other > CubicSDR. You will need to define
what device the app is going to use. With
that selected, pressing the start button
kicks off the application. (1a) is the audio
signal. Right click the screen portion and
drag it either left of right to adjust. (2a) is
the modulation used to encode the data.
Three frequency fields (A) exist. The far-
right digits are the frequency drawn in the
centre. The centre value is the bandwidth.
The value to the left is the frequency you
wish to monitor. (B) is the display of the
captured signal. (C) is the waterfall
display. The received signal (D) is green.
Weaker signals or noise are a light blue.
(E) is an expanded view of the larger
waterfall display to permit finer tuning.Gqrx
A
B
C
CubicSDR
2a E
C
D
1a
A
B
D
1
2
3
4
5
A TALE OF TWO APPS
80 LXF260March 2020 7778March 20pov8i2p
TUTORIALS Process radio signals
In the image on page 78, the left SDR dongle is housed
in a metal case, and the right dongle is plastic. The metal
acts as a heat sink for the electronic components.
Considering the ADC work the unit is performing there’s
a chance the device will generate heat.
Using a $10 SDR to receive the ‘must have’ critical
weather broadcast is not a good design idea.on a desired frequency. If a weak signal is what you are
after, wideband antennas are not ideal.
Devices will have specifications on the different
features the device supports. Inexpensive SDR
dongles lack some of the technology that increases
performance and provides stability. An example of this
is temperature stabilisation circuitry.Under the receivercontrol tab there is a
gain control (1) to adjust the amplification
of the signal received. (2) is the audio gain
control for the application. The small black
screen is the audio signal frequency
displayed in real time. This audio gain in
the application is in addition to what your
PC provides. Note: if your PC’s gain is set
to maximum and the app’s gain control is
at the minimum you won’t hear any audio.
Under receiver options tab, (3) is the local
broadcast frequency. (4) Mode is the
type of modulation, in our example FM.
Under the FFT settings tab, (5) divides
the far-left screen between signal screen
(black portion) and the waterfall screen
(blue/yellow mix).
On the main menu bar is a button to get
the application running. You may berequired to establish what device the
application is going to use. Ensure Realtek
RTL2838UHIDIR is the selected device.
(A) displays the broadcast frequency.
(B) is the captured signal. (C) is the
waterfall screen that shows the signal over
time–waterfall means the signal falls off
the bottom of the screen. (D) is the
received signal displayed in yellow. Notice
other yellow tracings for other signals.
The gain control (1) impacts the status
of both (B) and (C/D). If you increase the
gain of a receiver, you are amplifying what
is received. This includes the signal you
want, (B/D) but it also includes all the
other signals, which is why the screen
has more yellow than blue on it. Increase
the gain and you are amplifying noise
along with thesignal.Now set up the second application. Turn
off Gqrx before starting. Select Menu >
Other > CubicSDR. You will need to define
what device the app is going to use. With
that selected, pressing the start button
kicks off the application. (1a) is the audio
signal. Right click the screen portion and
drag it either left of right to adjust. (2a) is
the modulation used to encode the data.
Three frequency fields (A) exist. The far-
right digits are the frequency drawn in the
centre. The centre value is the bandwidth.
The value to the left is the frequency you
wish to monitor. (B) is the display of the
captured signal. (C) is the waterfall
display. The received signal (D) is green.
Weaker signals or noise are a light blue.
(E) is an expanded view of the larger
waterfall display to permit finer tuning.Gqrx
A
B
C
CubicSDR
2a E
C
D
1a
A
B
D
1
2
3
4
5
A TALE OF TWO APPS