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Re: explaining i/q

From: Kristoff
Subject: Re: explaining i/q
Date: Wed, 4 Nov 2020 02:15:29 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0


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?

kristoff - ON1ARF

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