Learning and understanding I/Q from the radio

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  • Updated 3 years ago
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Hello all,

I'm a programmer.  I've done a fair amount of signal analysis but never in the form of I/Q.  Most of the stuff I've done has been on raw signal data.

I've done a little reading on the I/Q stuff I've been able to find on the internet but I would like to understand it better.

In my software I've gained full access to the Dax Audio streams, Opus stream and got them nailed.  Now I'm playing with the I/Q output.  I'd like to figure out what I can get from it.

Any directives to what comes out of the Flex and ways to process/deal with it would be very much appreciated.

Of course this kind of question generally results in people asking what you want to do with it.  The answer to that is really open ended:

I'd like to play with writing a skimmer for CW, digital modes, etc

There has been a lot of talk about DXSPOTS but for a guy like me often the DXSPOT points to a station I can't even hear with my limited antennas.  I'd like to use I/Q data to create a map of what I can hear.

I'd like to play with a "signal searcher".  For this I have considered a mode that would scan the I/Q output, find what appear to be signals, tune to them and try to determine what they are or decode them.

Anyway you get the idea.  If I don't get a lot of pointers here I'll start to take the stream apart myself and see what I can figure out.  I've searched here and found one other good post on the I/Q stream.  Just looking for more.

Thanks - 73 - Mark WS7M
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Mark - WS7M

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Posted 3 years ago

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Andrew O'Brien

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I'd like to be able to take an I/Q stream and have any RSID over the stream's bandwidth detected and reported. 
Andy K3UK
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Mark - WS7M

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Agreed.
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Eric - KE5DTO, Official Rep

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Official Response
Mark,

Have you already read through the original SDR for the masses QEX articles?  If not, I would recommend starting there: http://www.flexradio.com/resources/articles/.
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Mark - WS7M

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Ok didn't know these were there!  Nice... Thanks!
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Ria - N2RJ, Elmer

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I use CW skimmed by Alex, VE3NEA to skim up to 4 bands. I combine my telnet streams to one single one. Works pretty good.

Read the articles as suggested but the reason SDRs used I/Q was for image rejection. Otherwise if you just have a single signal you'll get plus and minus the LO and it will be of no use:
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Mark - WS7M

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Hi Ria, I understand the reason, I want to understand the data better and how to use it for reasons like you mention.