Tuesday, December 15, 2015

If I Could Modulate A City

I wish I could find it but long ago I was reading about some amateur radio operators performing tests in the 10 GHz band. The would drive to the tops of nearby mountains, point their equipment at each other and talk to each other to test their equipment. Despite the high frequency, they were only operating on an FM voice mode. (I don't remember if it was this site but it seems like a good candidate.) Part of me was disappointed but I also know that it's 10 freaking GHz on home-made equipment! They were doing point-to-point links, which is what you'd expect for that frequency.

Now I can't remember if the chicken or the egg came first, but recently I made the connection between high-frequency, long-distance (over the horizon), wireless communication and city light pollution.

I delved into learning photography for a while in my life. If you ever decide to take long-exposure pictures of the stars, everyone will recommend getting as far away from cities as possible. This is because the glow of the city lights can be seen in those long-exposure photos even though the city is beyond the horizon. (Just look at the glowing horizon in some of these pictures.)

Me: Wait. Light seen beyond the horizon?
Smart me: Yes.
Me: So you're saying light doesn't follow a straight path?
Smart me: That's not at all what I'm saying. Are you crazy?

The light gets beyond the horizon because of tropospheric scatter, which is the atmosphere making the light/RF energy scatter in different directions. Yes that link to the Wikipedia article on tropospheric scatter is much better than what I could explain. (People are doing this at rates of up to 20 Mbit/s?! And you need kWs of power? Awesome!) Even those 10 GHz guys know about this. But that's pretty cool, right? Communicating wirelessly beyond the horizon by making the atmosphere "glow."

If you were some sick, crazy person who happened to have the power to turn an entire city's power on and off at will, you could do it in a way that communicated information to your sick, crazy friend who lives just down the freeway a hundred miles or so.

You: So in the title you said "I." Are you that sick, crazy person?
Me: No. I did say "if."

Now that I've written about it I can stop thinking about it. I feel like Gary Clark Jr. right now when he sang, "Bright lights, big city going to my head / I don't care no / 'Cause you don't care, no"

Sing it Gary.