# Is DBPSK Differential?

**URL:** <https://www.ruby-forum.com/t/is-dbpsk-differential/236910>\
**Category:** GNU Radio\
**Created:** [October 10, 2013, 7:36pm UTC](https://www.ruby-forum.com/t/is-dbpsk-differential/236910 "2013-10-10T19:36:19Z")\
**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:** [October 10, 2013, 7:36pm UTC](https://www.ruby-forum.com/t/is-dbpsk-differential/236910/1 "2013-10-10T19:36:19Z")

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I am wondering if it is my understanding is wrong here.

In my ongoing saga (I have been trying to get a flowgraph that worked in  
3.6 working in 3.7.2 and it just wont) examining the bits out of the  
demodulator when fed with 01111110 AX25 flags, the DBPSK module in GR3.6  
appears to be differentially coded and always outputs 1000001, but in  
3.7 it isn’t consistent, sometimes it is 1000001 and sometimes 01111110?  
My understanding of DBPSK is that to send a 1 the phase shift is 180  
degrees and for a zero there is no phase shift. This means when a signal  
is transmitted there is no need to sync to the phase ambiguity. That  
being the case, one should never see what I see in 3.7.2 - it looks more  
like the DBPSK demodulator is actually a BPSK demodulator and D means  
something else?

I also notice a few more options in 3.7 - Core Affinity and Min Output  
Buffer. I don’t think there are connected but would like to know what  
they are.

Mike

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**Author:** ![vh1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/278dde/32.png) [@vh1](https://www.ruby-forum.com/u/vh1)\
**Post date:** [October 27, 2013, 9:27am UTC](https://www.ruby-forum.com/t/is-dbpsk-differential/236910/2 "2013-10-27T09:27:47Z")

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Mike W. wrote in post #1124197:

> I am wondering if it is my understanding is wrong here.
> 
> In my ongoing saga (I have been trying to get a flowgraph that worked in  
> 3.6 working in 3.7.2 and it just wont) examining the bits out of the  
> demodulator when fed with 01111110 AX25 flags, the DBPSK module in GR3.6  
> appears to be differentially coded and always outputs 1000001, but in  
> 3.7 it isn’t consistent, sometimes it is 1000001 and sometimes 01111110?  
> My understanding of DBPSK is that to send a 1 the phase shift is 180  
> degrees and for a zero there is no phase shift. This means when a signal  
> is transmitted there is no need to sync to the phase ambiguity. That  
> being the case, one should never see what I see in 3.7.2 - it looks more  
> like the DBPSK demodulator is actually a BPSK demodulator and D means  
> something else?
> 
> I also notice a few more options in 3.7 - Core Affinity and Min Output  
> Buffer. I don’t think there are connected but would like to know what  
> they are.
> 
> Mike

I was just me using DBPSK then? Can we have this block removed from the  
tree - it seems redundant anyway as the PSK block can be configured to  
do DBPSK and works as expected.

Mike