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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: Tue, 20 Aug 2013 12:09:40 -0400

On Fri, Aug 16, 2013 at 1:43 AM, Volker Schroer <address@hidden> wrote:
> Am 14.08.2013 23:45, schrieb Tom Rondeau:
>> 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
>> 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.
> Tom,
> thanks for the info. I'll see if I can fix it, otherwise I'll report a bug.
> I'm using qwt-5.2 and pyqwt-5.2  on my system ( gentoo)
> -- Volker

Hi Volker,

Looks like this is specifically a Qwt 5.2 issue. I've resolved another
minor problem, but I'm seeing what you are seeing now by moving back
from Qwt 6. I'm working on a fix for it.

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