This is a great thing to try to figure out. If we can come up with an answer that gives someone a feel for why I/Q is used in SDR in 10 minutes, and does not include phasors, exponentials to a complex power, a derivation of any equation, the concept of orthogonality, etc. ... it will win a Nobel prize in education.
On Tue, Nov 3, 2020 at 4:56 AM gilles rubin <rubingil...@yahoo.com> wrote: > Hello, > > You can have a look here > The Concept of Frequency | Wireless Pi > <https://wirelesspi.com/the-concept-of-frequency/> > > The Concept of Frequency | Wireless Pi > <https://wirelesspi.com/the-concept-of-frequency/> > > Qasim Chaudhari CEO of Wireless Pi is great ! You will find plenty of > information on his website. > > Gil. > > > Le mardi 3 novembre 2020 à 00:06:02 UTC+1, Kristoff <krist...@skypro.be> > a écrit : > > > 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 > the 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 > > > > >
