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## explaining i/q

**From**: |
Kristoff |

**Subject**: |
explaining i/q |

**Date**: |
Tue, 3 Nov 2020 00:02:29 +0100 |

**User-agent**: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |

Hi all,

`I was watching the webinar of Heather on GNU Radio today, when it came
``to me that one of the most difficult part doing a presentation of GNU
``Radio is the data-types, .. and especially these 'complex numbers'.
``The problem, or at least for me, is that when you mention 'GNU Radio
``complex numbers', you also have to mention iq-signals, which is a topic
``that is very difficult to explain in 10 seconds to an audience who has
``never seen anything about i/q sampling before.
`

`I have been thinking on how to explain the concept of I/Q signalling in
``just a few lines, e.g. in the context of -say- a workshop on GR.
`
I have this idea in my head:
Statement:

`The main difference between sampling with reals ('floats') and i/q
``sampling with complex numbers, is that the latter does not only provide
``theĀ instantaneous value (voltage) of a signal at a certain point of
``time, but also includes phase information (i.e. the slope of the signal
``at that point).
`
To make this visual:
Take half a sine-wave and plot it out for every 45 degrees.

`This gives you 5 points: 0 (0 degrees), sqrt(2)/2 (45 degrees), 1 (90
``degrees), sqrt(2)/2 (135 degrees) and 0 (180 degrees).
`

`Now look at the 2nd and the 4th point (45 degrees and 135 degrees), if
``you sample this using only real/float values, these two points are
``exactly the same (sqrt(2)/2). Just based on these values by themselves
``(i.e. remove all other points from the graph), there is no way you can
``tell that at the first point (45 degrees) the graph was going up, while
``at the 135-degrees point the graph was going down.
`

`So, ... what i/q sampling does, is for every point "x", it not only
``provide the value of the graph at that point of time, but also
``information of the slope of the graphs at that time.
`

`This also explains while i/q sampling is done by not just taking the
``value of a signal at point "t", but also at 1/4 period later (which is
``the information you need to determine the 'slope' of that graph at point
``'t')
`
So, ... is this statement correct?

`If it is more-or-less correct and it can help provide a basic mental
``image of the concept of i/q sampling, I would be more then happy! :-)
`
73
kristoff - ON1ARF

**explaining i/q**,
*Kristoff* **<=**
**Re: explaining i/q**, *David Hagood*, `2020/11/02`
**Re: explaining i/q**, *Jeff Long*, `2020/11/02`
**Re: explaining i/q**, *Aditya Arun Kumar*, `2020/11/02`
**Re: explaining i/q**, *Anon Lister*, `2020/11/02`
**Re: explaining i/q**, *gilles rubin*, `2020/11/03`