# Fwd: QTGui Number Sink, Demodulation Problems

**URL:** <https://www.ruby-forum.com/t/fwd-qtgui-number-sink-demodulation-problems/232511>\
**Category:** GNU Radio\
**Created:** [October 13, 2014, 10:31pm UTC](https://www.ruby-forum.com/t/fwd-qtgui-number-sink-demodulation-problems/232511 "2014-10-13T22:31:22Z")\
**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:** [October 13, 2014, 10:31pm UTC](https://www.ruby-forum.com/t/fwd-qtgui-number-sink-demodulation-problems/232511/1 "2014-10-13T22:31:22Z")

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The purpose of my current experiments is to create a 16QAM transmitter  
and  
receiver, with UDP sources/sinks, and using bladeRFx40’s to  
transmit/receive.

I’m using Number sinks to check values at various points of my  
flowgraph.  
If I use a constant source value of 1, a float input type to a Number  
sink  
displays a “1”, but a byte input type displays a “0”. This is  
problematic  
because I’m trying to troubleshoot the QAM demodulator which has an  
output  
type of byte.

I’ve got Number sinks throughout the flowgraph. The source, modulator,  
and  
polyphase clock all output correct values for samples/symbols of “1111”  
but  
the demodulator is giving outputs of “0”.

Are these bugs, or am I doing something wrong?  
Also, I tried replacing the QAM mod/demod blocks with 8PSK blocks and  
still  
have the save problem.

Thanks in advance for any assistance.

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<div class="post-metadata">

**Author:** ![quangn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/q/e47774/32.png) [@quangn](https://www.ruby-forum.com/u/quangn)\
**Post date:** [October 16, 2014, 6:58pm UTC](https://www.ruby-forum.com/t/fwd-qtgui-number-sink-demodulation-problems/232511/2 "2014-10-16T18:58:23Z")

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On Mon, Oct 13, 2014 at 4:30 PM, Jason N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> I’ve got Number sinks throughout the flowgraph. The source, modulator, and  
> polyphase clock all output correct values for samples/symbols of “1111” but  
> the demodulator is giving outputs of “0”.
> 
> Are these bugs, or am I doing something wrong?  
> Also, I tried replacing the QAM mod/demod blocks with 8PSK blocks and  
> still have the save problem.
> 
> Thanks in advance for any assistance.

Yeah, this was a bug. Looks like a very stupid mistake on my part.

I’ve pushed a fix that mostly works, but we can’t really fix it without  
breaking the api. It should work fine now for char, short, and float  
inputs. There’s a note in the block’s documentation about this.

Tom

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<div class="post-metadata">

**Author:** ![quangn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/q/e47774/32.png) [@quangn](https://www.ruby-forum.com/u/quangn)\
**Post date:** [October 28, 2014, 9:13pm UTC](https://www.ruby-forum.com/t/fwd-qtgui-number-sink-demodulation-problems/232511/3 "2014-10-28T21:13:51Z")

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Tom,

Thanks for the quick bug fix Re: the number sinks. In the interim I’ve  
been  
troubleshooting by dumping output to a binary file and discovered other  
mistakes on my part. But once again I’m at an impasse. I captured some  
data  
which I view in the terminal using xxd -b filename.

The interesting thing is that the first portion of the file is all 1’s  
“1111 1111 1111”, which is the correct output that I’m looking for.  
However, it transitions to outputting “0101 0101 0101” and stays with  
that  
output apparently indefinitely. Could this in some way be caused by the  
Polyphase Clock Sync?

Thanks,  
-Jason