Here’s a YouTube video that’s got a bit of pencil math (so it doesn’t drone on) and oscilloscopes (for the ham guys), so it’s got a bit for everyone .
https://m.youtube.com/watch?list=PLvOgjCaG0WzDAF1Um894vv95mrcyortOB&v=h_7d-m1ehoY > On Nov 4, 2020, at 7:52 AM, Kristoff <krist...@skypro.be> wrote: > > Jef, > > > Concerning the term "slope". Well, I also have my doubts about it. I think > that for a lot of people, this would create the assumption that the signal > then goes from the 'i' value to the 'q' value in a straight line, which is > -as we know- not the case. > > Sometimes it helps to -at first- give a very basic mental image of something, > and -at the end, when people understand the topic- "correct" that image with > a more correct one, or just point them to some youtube video that explains > the topic in more detail. > > > Anycase,this is indeed all an interesting exercise in braking down concepts > into very small steps. > > The amateur-radio community is a bit strange as most people do have a > technical background, but for a large number of hams, that is mainly based on > assumptions or "that's what they said in the ham-radio courses", without > understanding the full technical details, especially topics that are highly > based on math. > For most hams, "SDR" is just "that piece of software you install on your > computer to look at waterfall graphs". > > So we have a very long way to go. :-) > > > 73 > kristoff - ON1ARF > > > >> On 4/11/2020 02:21, Jeff Long wrote: >> It's more important to give people some mental picture than to make sure >> it's completely correct. But, I would not use the "slope" terminology. The >> important things are, as you've said, (1) with the complex type, you can >> have a signal at baseband that is not symmetric, and (2) the price for this >> is doubling the amount of data needed. The signal you deal with at baseband >> is the same signal that is seen centered on the RF carrier. >> >> I don't see a great way to talk about "phase" without going into the math. >> It is important to get into "phase" when you talk about any modulation >> fancier than slow FSK. >> >> Good luck. Hope you find the right balance between useful, digestible, and >> correct. >> >> On Tue, Nov 3, 2020 at 7:20 PM David Hagood <david.hag...@gmail.com >> <mailto:david.hag...@gmail.com>> wrote: >> >> I am sorrowful that you have decided you are going to stick with an >> explanation that is fundamentally incorrect. I know how direct >> conversion systems work - I design the software for them for a >> living. >> What you are basing your mental model on is an optimization for >> the case >> where the system is both sub-sampling the signal and going digital in >> the same operation. However, in many extremely high sample rate >> systems, >> the signal is brought down to baseband by mixing it with analog >> quadrature signals - that's the place where I and Q come from - and I >> assure you the only "delay by 90 degrees" is in the creation of the >> quadrature LO signals, not in the sampling of the actual data. But >> I've >> been around the Sun enough times to know that since you have decided >> upon this course and don't seem to want to change, there's no >> point in >> continuing to try to help. >> >> > >
