Nice! I especially like the use of dogs as local oscillators. On Tue, Dec 8, 2020 at 10:29 AM Qasim Chaudhari <qasim.chaudh...@gmail.com> wrote:
> Hi everyone > Hope you're doing well. Someone pointed me towards this discussion on > the mailing list and I thought that it's a great topic to explain without > complex numbers, phasors, orthogonality, etc. So I wrote about it for a > true beginner. > > Instead of focusing on a small length, my main purpose was to produce > some beautiful figures that can help one grasp why both I and Q samples are > required. > > https://wirelesspi.com/i-q-signals-101-neither-complex-nor-complicated > > Cheers, > Qasim > > From: Kristoff <krist...@skypro.be> > To: discuss-gnuradio@gnu.org > Subject: Re: explaining i/q > > 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 > >
