# GRC bug - channel limitation in QT GUI Frequency Sink

**URL:** <https://www.ruby-forum.com/t/grc-bug-channel-limitation-in-qt-gui-frequency-sink/242381>\
**Category:** GNU Radio\
**Created:** [June 19, 2015, 5:39pm UTC](https://www.ruby-forum.com/t/grc-bug-channel-limitation-in-qt-gui-frequency-sink/242381 "2015-06-19T17:39:02Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [June 19, 2015, 5:39pm UTC](https://www.ruby-forum.com/t/grc-bug-channel-limitation-in-qt-gui-frequency-sink/242381/1 "2015-06-19T17:39:02Z")

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If you set the number of channels in the Freq sink block \> 10 (in my  
case  
11), grc will throw an error.  
“if len(labels[i]) == 0:  
IndexError: list index out of range”

Upon further investigation, the source code it generates only has 10  
arguments in the alphas, colors, widths and labels fields. If I manually  
edit the source and add an 11th argument to the alphas, colors, widths  
and  
labels fields, then run the code from a terminal, it runs no problem.  
Seems  
like a GRC only error.

Just wanted to report.

thanks,  
-b

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**Author:** ![ben\_Gee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/85f322/32.png) [@ben\_Gee](https://www.ruby-forum.com/u/ben_Gee)\
**Post date:** [June 19, 2015, 5:43pm UTC](https://www.ruby-forum.com/t/grc-bug-channel-limitation-in-qt-gui-frequency-sink/242381/2 "2015-06-19T17:43:07Z")

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On Fri, Jun 19, 2015 at 11:38 AM, ben Gee [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Just wanted to report.
> 
> thanks,  
> -b

Yep, that’s a known limitation. You can see in the GRC file that there’s  
no  
good way to arbitrarily extend a list in the XML, so we made a decision  
to  
limit it to this many entries.

Tom