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Re: [Discuss-gnuradio] Meaning of Center Frequency in QT GUI Sink / QT W

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Meaning of Center Frequency in QT GUI Sink / QT Waterfall Sink
Date: Wed, 14 Aug 2013 17:45:26 -0400

On Wed, Aug 14, 2013 at 6:29 AM, Volker Schroer <address@hidden> wrote:
> Hi,
> what is the meaning of the variable "Center Frequency" in the qt_gui_sink /
> qt_waterfall_sink ?
> If I remember well, in pre 3.7 version it served as base of the  x - axis
> legend.
> Now, if I choose a value > bandwidth/2 the spectrum will not be displayed.
> Do I misinterpret the meaning  of "Center Frequency" or is this a bug ?
> -- Volker


This sounds like a bug. Someone else reported some related issues with
this sink in 3.7, too. Probably a versioning issue that I didn't
properly take care of with the update.

Now, the main reason this would have slipped through is because I'm
trying to get rid of the qt_gui_sink. Since I've split out the
different sinks, it doesn't make sense to keep them in two different
places with duplicated code that can't easily be shared (which can
then lead to mistakes like this). I will be moving to a new structure
for the qtgui_sink_X blocks that is just a tab container for the other
individual classes to simplify the code.

Now, you're also saying that it's a problem with the
qt_waterfall_sink? That's more surprising, but again, probably a
Qt/Qwt version issue and should be a simple fix once identified. Not
sure when I'll be able to get to it, so either submit a patch or at
least open a bug report on our Issues Tracker to make sure I remember
to get to it soon.

But remember, setting the center frequency is just a display issue. It
simply sets the tick labels on the x-axis and nothing more.

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