‘Click Tune’ Frequency Changes with the FFT GUI

A useful SDR operating aid with a GNU Radio DSP is the ‘click tune’ function.  ‘Click Tune’ means that the user can left click the FFT GUI to center the desired signal in the passband.  In other words, when monitoring a band of frequencies, the desired signal can be selected simply by left clicking on that signal in the FFT display.

Implementation of the built in ‘click tune’ function is simple.  That said, a downside of this simple, basic functionality, is every selection from the FFT simply adds or subtract baseband frequency tuning data for the tuning buffer.  In order to select a specific second signal and center it in the passband, it is necessary to return the buffer data to “0”.  In practice, after a initial signal has been selected, it is necessary to select “0” on the FFT display to re-initialize the frequency shift buffer, in order to select and center a second signal.

If a Tune WX GUI Slider widget has been included in the flow graph, a simple command in the GUI FFT Sink Properties box implements click tune.  The two Properties boxes below illustrate the complete process.  To get full functionality of ‘click tune’ make the frequency range of the Tune widget equals or exceeds the FFT display range.

WX GUI Slider Properties with the ID field parameter ‘tune’.  This slider adjusts the frequency from the Operating GUI.
GUI FFT Sink Properties with ‘tune’ entered in the Freq Set Varname field.  This command makes it possible to select frequencies by left clicking on the FFT Sink GUI.

NOTE;  The ‘click tune’ function does not appear to work with the GUI Waterfall Sink with my version of GNU Radio.  And, I am uncertain whether ‘click tune’ can be implemented with the QT GUI widgets.

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