# 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/243135>\
**Category:** GNU Radio\
**Created:** [August 25, 2015, 2:28am UTC](https://www.ruby-forum.com/t/rtl-sdr-and-grc3-7-8-problem-format-error/243135 "2015-08-25T02:28:00Z")\
**Posts on this page:** 1\
**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 25, 2015, 2:28am UTC](https://www.ruby-forum.com/t/rtl-sdr-and-grc3-7-8-problem-format-error/243135/1 "2015-08-25T02:28:00Z")

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Thanks Marcus yet again. In the past gr-osmosdr simply built seamlessly  
along with gnuradio. Not this time. Don’t know why. My solution was  
to  
delete the gr-osmosdr files from the home directory and git clone from  
the  
Osmosdr website. The installation went smoothly and the RTL SDR  
receiver  
demos all run as expected. Just in time. And, I’ll not throttle again  
against the Qt GUI block.

Regards,  
John Petrich

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

Marcus L.:

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gr-osmosdr you’re using is out-of-date with respect to the GR that is  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.