A TALE OF TWO APPS
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 be required 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 farright 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.