# RTL SDR and GRC3.7.8 problem: format error

**URL:** <https://www.ruby-forum.com/t/rtl-sdr-and-grc3-7-8-problem-format-error/243128>\
**Category:** GNU Radio\
**Created:** [August 24, 2015, 8:29pm UTC](https://www.ruby-forum.com/t/rtl-sdr-and-grc3-7-8-problem-format-error/243128 "2015-08-24T20:29:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\
**Post date:** [August 24, 2015, 8:29pm UTC](https://www.ruby-forum.com/t/rtl-sdr-and-grc3-7-8-problem-format-error/243128/1 "2015-08-24T20:29:17Z")

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Ever since I updated to GRC3.7.8 none of my RTL SDR demos will run in  
GRC.  
The error messages are the same: " list contains an invalid format".  
Attached is the .grc file of a basic RTL Qt test flow graph authored  
using  
GRC3.7.8, and the .odt file with the complete error message. GRC  
detects  
the RTL device, and cites format errors. Are others having this  
problem  
with GRC3.7.8? I am anxious to resolve this problem because I have  
scheduled a GRC presentation in the near future.

Regards,

John Petrich

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**Author:** ![johnpetterson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/41988e/32.png) [@johnpetterson](https://www.ruby-forum.com/u/johnpetterson)\
**Post date:** [August 24, 2015, 8:34pm UTC](https://www.ruby-forum.com/t/rtl-sdr-and-grc3-7-8-problem-format-error/243128/2 "2015-08-24T20:34:32Z")

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On 08/24/2015 02:26 PM, John Petrich wrote:

> Regards,
> 
> John Petrich

Did you re-build gr-osmosdr against 3.7.8? My suspicion is that the  
gr-osmosdr you’re using is out-of-date with respect to the GR that is  
calling it.

Also, you have a throttle block in between your hardware source, and  
your Qt GUI block. Don’t do that. You never need a throttle when  
you’re using  
real hardware.