Re: explaining i/q

[Kristoff]

David,



On 4/11/2020 01:18, David Hagood 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.


As mentioned, the goal here is to explain I/q sampling in 5 minutes to a 
group of average hams (i.e. who have limited knowledge of advanced 
electronics and even less of math).
The question to answer is this:
what is i/q sampling and why does it it matters for him/her when 
creating a GNU Radio flowgraph.


So, you do not have to convince me how i/q sampling works, you have to 
convince this audience.


So, feel free to explain in semi-tech (no math) talk in 5 minutes *why* 
SDR uses i/q sampling.
What is the PURPOSE of i/q sampling?



73
kristoff - ON1ARF