Re: [Discuss-gnuradio] trouble with QAM mod/ WX GUI Constellation Sink

[Martin Braun]

There should be enough free resources, no need to pay big $$$ for books.
Other than what you list, have a look at
http://gnuradio.org/redmine/projects/gnuradio/wiki/SuggestedReading.

M

On 07/17/2015 06:19 PM, Bill Eaton wrote:
>> ... so I recommend you get an intro book to digital comms and map what
> they
>> say to the GNU Radio examples.
> 
> Yeah. I was afraid it might come to this. Do you have any recommendations?
> Most digital comms textbooks are pretty pricey, and I'd hate to spend time
> and money on one that might not be a good fit.
> 
> There are free options. There's the MIT course and the Lapidoth PDF book. I
> suspect I might prefer a real printed book with nice graphics.
> 
> Thanks in advance,
> 
> Bill Eaton
> 
> 
> 
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On
> Behalf Of Martin Braun
> Sent: Friday, July 17, 2015 3:04 PM
> To: address@hidden
> Subject: Re: [Discuss-gnuradio] trouble with QAM mod/ WX GUI Constellation
> Sink
> 
> On 17.07.2015 14:56, Bill Eaton wrote:
>>> What I meant was that you plot the result of your timing + phase 
>>> recovery
>>
>>> into an XY plot, that would take care of those additional points
>> you're seeing.
>>
>> I have to confess that I don't even know what that means or how to go 
>> about accomplishing it. I have to take baby steps because I'm a baby.
>> ;-) If you could point me to an example or some other things to try, 
>> that would be helpful.
> 
> OK, this is starting to get into basics of digital comms and this mailing
> list is probably not a good place for that.
> 
> In brief, what you're plotting is the output of the QAM Mod -- which is
> *not* a QAM constellation, but rather the complex baseband signal that can
> be transmitted. This does include the QAM constellation.
> 
>> I looked through the examples that ship with GNURadio and didn't see 
>> anything obvious. Also, I looked through the GRC block tree to see if 
>> I could try something. There's a Synchronizers section. Something from
> there?
> 
> Try the examples in gr-digital.
> 
>> You thought maybe it was oversampled. It occurred to me that maybe the 
>> X-Y chart rate should be samp_rate/8, but I tried that and the chart 
>> still look largely the same.
> 
> That's not quite the right terminology, but if you plotted only a subset of
> the samples of your signal, you would see the constellation.
> 
> It seems you're fine using GNU Radio itself, so I recommend you get an intro
> book to digital comms and map what the say to the GNU Radio examples.
> 
> Cheers,
> Martin
> 
> 
>>
>>  
>>
>> mlist_qam_constellation_xy.grc.png
>>
>>  
>>
>>  
>>
>>  
>>
>> -----Original Message-----
>> From: address@hidden
>> [mailto:address@hidden On 
>> Behalf Of Martin Braun
>> Sent: Friday, July 17, 2015 1:20 PM
>> To: address@hidden
>> Subject: Re: [Discuss-gnuradio] trouble with QAM mod/ WX GUI 
>> Constellation Sink
>>
>>  
>>
>> On 17.07.2015 12:43, Bill Eaton wrote:
>>
>>> From Martin Braun:
>>
>>>
>>
>>>> My preference is to build the demod/sync chain with it's own blocks,
>>
>>>> and then just output the complex symbols
>>
>>>
>>
>>>> into either an X/Y plot (WX) or the QT Constellation Sink
>>
>>>
>>
>>> Even an X/Y plot ends up looking funny. I've attached a GRC file for
>>
>>> X-Y, and when you turn on persistence, it looks better. But it's very
>>
>>> strange. Maybe my bits_per_symbol is wrong. Or maybe the sample rate
>>
>>> for the X-Y chart should be different than the random sample rate?
>>
>>> Here's the 4 QAM X-Y.
>>
>>  
>>
>> Your plot looks fine, it's just oversampled (but perfectly 
>> time-synchronized, I'm guessing this is post-pulse shaping + noise?).
>>
>>  
>>
>> What I meant was that you plot the result of your timing + phase 
>> recovery into an XY plot, that would take care of those additional 
>> points you're seeing.
>>
>>  
>>
>> M
>>
>>  
>>
>>  
>>
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