# Doubt in digital modulation chain

**URL:** <https://www.ruby-forum.com/t/doubt-in-digital-modulation-chain/230825>\
**Category:** GNU Radio\
**Created:** [July 7, 2014, 10:11pm UTC](https://www.ruby-forum.com/t/doubt-in-digital-modulation-chain/230825 "2014-07-07T22:11:01Z")\
**Posts on this page:** 2\
**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:** [July 7, 2014, 10:11pm UTC](https://www.ruby-forum.com/t/doubt-in-digital-modulation-chain/230825/1 "2014-07-07T22:11:01Z")

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Dear All,

I am constructing the flow graph(screen capture, grc) attached.

# I am expecting the data at the output of packed-to-unpacked block to be the same as the data at the output of differential decoder, except for some stray bits in the beginning. When I search for patterns in the transmit chain, in the receive chain, I don’t get any match. This it the code(also attached) that I use to compare data in the transmit chain and the receive chain.

import scipy

template\_len = 20

# temp = scipy.fromfile(open("/tmp/diff-encode-out.bin"), dtype=scipy.uint8, count=1000) template = temp[100:template\_len+100] print len(template) match = False rec = scipy.fromfile(open("/tmp/rec-map-out.bin"), dtype=scipy.uint8, count=100000) for i in range(9950): if (template == rec[i:template\_len+i]).all(): print i break

The program works for BPSK, but fails to find pattern in QPSK, DQPSK  
etc.  
Would anyone know what is going wrong in my flow-graph?

Thank you in advance.

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**Author:** ![Manu\_T\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea5d25/32.png) [@Manu\_T\_S](https://www.ruby-forum.com/u/Manu_T_S)\
**Post date:** [July 14, 2014, 3:07pm UTC](https://www.ruby-forum.com/t/doubt-in-digital-modulation-chain/230825/2 "2014-07-14T15:07:51Z")

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On Mon, Jul 7, 2014 at 4:08 PM, Manu T S [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ## ====================== count=100000)
> 
> Manu T S

Hi Manu,

This generally looks correct, but you’ll want to see about that map  
block  
(or the constellation pre-diff coding) to translate the symbols-\>bits  
correctly. And if you think you’ve done it right, try again 🙂

Tom