General description
In phase (I) and Quadrature (Q) signal components are extracted from Intermediate Frequency (IF) signal multiplying it with sine and cosine. After multiplication, I and Q components are low pass filtered in order to eliminate aliased components. I and Q samples are plotted as x and y coordinate display. The user can select freely carrier frequency from where down conversion is done. The user can adjust the bandwidth of the IF signal with low pass filter. The If signal is digitally modulated. So the user can find correct synchronization time adjusting the downsampling and the start offset parameters.
Configuration
When the Config button is pressed, the following configuration dialog is opened.
Parameters
Carrier
The carrier frequency from where IQ separation is done.
Bandwidth
The width of low pass filter which is used to filter I and Q signal after sifting the signal to the base band.
Down sampling
Every N:th of I and Q signals are plotted on the screen.
Start offset
Plotting of I and Q signals is started from N:th sample.
Samples in Display
Number of I and Q samples that are plotted into display.
Display Max Extent
The maximum extent of the signal plot area. This parameter is used when the user zooms out the display.
Drawing Mode
I and Q pairs can be connected with a line or they can be plotted with circles or crosses.
Coherent
If received signal is BPSK or QPSK modulated signal, the coherent IQ separation is able to detect state transitions. This ensures that constellation does not rotate.
Display commands
Pressing the right mouse button in the plot area the pop down menu is opened. There are the following commands in the pop down menu.
Stop/Start
Display can started or stopped
Auto Scale
When auto scale is enabled, display is scaled automatically in order to fit IQ constellation optimally on the display. If autoscale is not on, the user can use left button to scale the interesting plot area with the mouse.
Zoom Out
Using Zoom Out command, the user can return display on the maximum size. The maximum size depends on the maximum extent parameter which is set from the configuration menu.
Grid
When selected, grid is drawn on the display.
Copy to Clipboard
Plot on the display is copied on the clipboard.
Help
Context sensitive help about IQ constellation display.
