# Frame Synchronization

**URL:** <https://www.ruby-forum.com/t/frame-synchronization/234531>\
**Category:** GNU Radio\
**Created:** [March 11, 2015, 8:28pm UTC](https://www.ruby-forum.com/t/frame-synchronization/234531 "2015-03-11T20:28:19Z")\
**Posts on this page:** 3\
**Page:** 1

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**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:** [March 11, 2015, 8:28pm UTC](https://www.ruby-forum.com/t/frame-synchronization/234531/1 "2015-03-11T20:28:19Z")

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Hello,

I’m trying to detect the start of a frame after demodulation. To do  
this,  
I’m using the ‘correlate access code - tag’ block. I want a tag to be  
placed at the end of the prbs used to frame sync so subsequent blocks  
can  
process the packet.

I’m attaching a screenshot of a test I’m doing with the block. I can’t  
get  
it to work. In the screenshot, I am appending a 32 bit long sync frame  
to  
320 bits of data for the correlate block to detect. When I make the data  
all 0’s, the correlate block detects nothing adding no tags to the  
stream.  
If I make the data random, tags are added at points in the stream which  
are  
not equal to the access code.

What am I doing wrong or how do I use this block correctly?

Thanks,  
Rich

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**Author:** ![reback](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@reback](https://www.ruby-forum.com/u/reback)\
**Post date:** [March 11, 2015, 8:31pm UTC](https://www.ruby-forum.com/t/frame-synchronization/234531/2 "2015-03-11T20:31:41Z")

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This is strange, I agree, but the frame detect sequence is passed into  
the  
Correlate Access Code block as a string, like: “1010101010”. It is this  
way  
for historical reasons.

–n

On Wed, Mar 11, 2015 at 12:26 PM, Richard B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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**Author:** ![reback](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b5ac83/32.png) [@reback](https://www.ruby-forum.com/u/reback)\
**Post date:** [March 11, 2015, 9:17pm UTC](https://www.ruby-forum.com/t/frame-synchronization/234531/3 "2015-03-11T21:17:02Z")

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Thank you Nick. That’s what I was doing wrong. Really appreciate that.

Rich