RE: [Discuss-gnuradio] Re: information theory -- follow up

[Ettus, Matt]

> But my main problem is the colour analogy. It doesn't really 
> account for a
> lot of things. If you're looking at a 60W blue light bulb 
> flashing signal at
> you, then someone turns on a 1 000 000W blue light source 
> behind it, you're
> not going to be picking up much useful information any more, 
> now are you?

This is kind of a loaded analogy, but even so, it is not true.  If your bulb
is flashing, it produces sidebands.  If you filter out the carriers (both
yours and the megawatt one), you can still receive the sidebands.

It is also misleading.  The are petawatt (maybe stronger) light sources all
around us (i.e. the sun, stars, etc.)  That doesn't mean that I can't see an
LED.  It just means I have to be closer to the LED to see it. 

Besides, I don't think anyone is saying that everyone should be allowed to
trasmit with a megawatt.  Just becuase spectrum might be open to all,
doesn't mean there won't be rules to limit your power.

> Even if the two lights were different colours it would be difficult.
> Basically any situation where you get washed out images, 
> glare, partial
> reflections, or any other visual problem show that just 
> because colours
> behave mostly like radio waves, and that we can still get 
> usually get useful
> information from them, doesn't mean there's infinite capacity there.

Very false.  Filtering separates color/frequencies.  

> Also consider what some people do with university crib 
> sheets. To get more
> on the page they will sometimes write in two different 
> colours, and wear 3D
> glasses to let them separate the green and the red, or 
> whatever colours they
> choose, by closing one eye or the other. But without the 
> glasses it's really
> quite hard to read. All the lenses really are are band pass 
> filters, which
> we already do with radio waves.

Exactly the point he's trying to make.  If you can't read the signal then
you need better glasses.