# Problem with the string of blocks: Packet Encoder - Packed to unpacked - Unpack k bits - Packet Deco

**URL:** <https://www.ruby-forum.com/t/problem-with-the-string-of-blocks-packet-encoder-packed-to-unpacked-unpack-k-bits-packet-deco/241235>\
**Category:** GNU Radio\
**Created:** [May 19, 2014, 4:48pm UTC](https://www.ruby-forum.com/t/problem-with-the-string-of-blocks-packet-encoder-packed-to-unpacked-unpack-k-bits-packet-deco/241235 "2014-05-19T16:48:03Z")\
**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:** [May 19, 2014, 4:48pm UTC](https://www.ruby-forum.com/t/problem-with-the-string-of-blocks-packet-encoder-packed-to-unpacked-unpack-k-bits-packet-deco/241235/1 "2014-05-19T16:48:03Z")

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Hi everybody,

I’m currently working with some modulations (M-QAM, M-PSK) and my  
results  
are almost the same for all of them. I’m sending a wav file which is a  
4-minute song and in reception I get just a few seconds of the song  
within  
cuts. It seems that I’m losing lots of packets in the process.

After trying lots of things, I’ve reduced my graph to the minimum,  
eliminating all the mod/demod modules, as you can see in the attached  
picture. However, I’m getting the same results than before, so I tend to  
believe that my problem is not in the mod/demod part of the graph but in  
the use of the following string of blocks:

Packet encoder - Packed to unpacked - Unpack k bits - Packet decoder.

As far as I know, these blocks do the following operations:

PACKET ENCODER: Converts float samples into bytes, each byte with 4  
symbols  
of 2 bits each.  
PACKED TO UNPACKED: Puts a symbol of 2 bits in a byte in the MSB  
position.  
UNPACK K BITS: The opposite of “Packed to unpacked” block.  
PACKET DECODER: The opposite of “Packet enconder” block.

Please, I would appreciate any help with this. I know that it’s a pretty  
basic graph but I don’t know what I’m doing wrong.

Thanks in advance!!

Ramiro Utrilla

P.D: I’m running GNU Radio 3.7.4 on a 64-bit PC with Ubuntu 14.04.

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<div class="post-metadata">

**Author:** ![rutrilla](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/5f8ce5/32.png) [@rutrilla](https://www.ruby-forum.com/u/rutrilla)\
**Post date:** [May 19, 2014, 4:51pm UTC](https://www.ruby-forum.com/t/problem-with-the-string-of-blocks-packet-encoder-packed-to-unpacked-unpack-k-bits-packet-deco/241235/2 "2014-05-19T16:51:49Z")

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You must include a throttle block just after the file source otherwise  
you  
will max out the CPU and things get messy as you have seen.

Mike

–  
Mike J. M0MIK BSc MIET  
Ettus R. Technical Support  
Email: removed\_email\_address@domain.invalid  
Web: [http://ettus.com](http://ettus.com)