# QT GUI frequency plot scale

**URL:** <https://www.ruby-forum.com/t/qt-gui-frequency-plot-scale/232530>\
**Category:** GNU Radio\
**Created:** [October 14, 2014, 10:09pm UTC](https://www.ruby-forum.com/t/qt-gui-frequency-plot-scale/232530 "2014-10-14T22:09:02Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [October 14, 2014, 10:09pm UTC](https://www.ruby-forum.com/t/qt-gui-frequency-plot-scale/232530/1 "2014-10-14T22:09:02Z")

</div>

Hi all,

I’m going through some of the GNU Radio tutorials and I noticed that the  
frequency axis for the QT GUI frequency sink is incorrect for real  
valued  
signals (e.g., sample rate of 10k shows -2.5k to 2.5k). I found a bug  
report (#541) from last year with the issue resolved in 3.7.0, but I’m  
working with version 3.7.2.1. I didn’t notice any other bug reports  
regarding this issue.

Note: The frequency plot in QT GUI sink is scaled correctly. Also,  
updating  
the sampling rate while the flow graph is running corrects the scale.

Regards,

Mike Rahaim  
PhD Candidate  
Boston University, Boston, MA

---

<div class="post-metadata">

**Author:** ![roa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/8e7dd6/32.png) [@roa](https://www.ruby-forum.com/u/roa)\
**Post date:** [October 15, 2014, 1:14am UTC](https://www.ruby-forum.com/t/qt-gui-frequency-plot-scale/232530/2 "2014-10-15T01:14:04Z")

</div>

On Tue, Oct 14, 2014 at 4:07 PM, Michael R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> updating the sampling rate while the flow graph is running corrects the  
> scale.
> 
> Regards,
> 
> Mike Rahaim  
> PhD Candidate  
> Boston University, Boston, MA

Hi Mike,

I think this was (should be) /fixed/ fixed in the 3.7.4 release. Check  
out  
the commit:

> <https://github.com/gnuradio/gnuradio/commit/d087c4186e64bdea8c10a2ab3fad9f2474e9c818>
>
> Was setting bandwidth to half what it should have. Tested QWT 5.2.0 - 6.1.0.

There was some back-and-forth I did between versions of QWT, and this  
seemed to be the last stray issue that I found.

Tom