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A candle in the wind, a whisper on the air


I hope the non-nerds will excuse another nerd post. But because of some of the email I get, I know that some of the readers here are nerds…

As we contemplate the fact that we are all energy hogs (you do contemplate that fact, don’t you?), I think it’s interesting to remind ourselves just how much can be accomplished with small amounts of energy. Let’s use an example from radio. To us modern digital folks, radio may seem like old stuff, antique almost. But all of our favorite toys depend on radio, from iPhones to WiFi.

Musicians are familiar with the concept of the octave. Octaves have to do with the doubling of a frequency. A piano keyboard, for example, covers seven octaves of sound. The human ear can hear about 10 octaves of sound. We can apply the concept of the octave to any phenomenon where wave forms and frequency are involved. This includes, of course, electromagnetic energy. If you go up about 40 octaves from the piano keyboard, you arrive at the frequency of light. The human eye can perceive less than an octave of light. Red light is the lowest frequency of light we can perceive; violet is the highest.

In between the frequencies of sound and light is radio, in a frequency range of 3,000 cycles per second (3 kilohertz, or 3 kHz) to 300 billion cycles per second (300 gigahertz, or 300 GHz). That’s a lot of octaves. What’s amazing about radio is that different frequencies travel around the earth in very different ways. For example, the frequency of radio waves emitted by your cell phone (around 1 GHz), can’t travel very far, because it can’t (usually) bend with the earth’s curvature or bounce back down to earth off the earth’s ionosphere. On the other hand, radio frequencies up to about 30 megahertz (30 mHz) can travel all the way around the earth under the right conditions, even with very little energy.

A candle is better at producing heat, actually, than light. A candle produces a meager 13 lumens of light and 40 watts of heat! That’s a huge amount of heat energy. And, by the way, the average human body runs on about 100 watts of energy, of which the brain consumes a fifth — 20 watts. The brain burns less energy than a candle. And though the energy used by the human body is a tiny fraction of the energy used by our cars, our bodies are not excellent examples of energy frugality.

Compare the energy richness of the sun with the energy frugality of the moon. The sun’s radiation produces about 342 watts per square meter on the earth’s surface, on average, during the course of a year. By comparison, the energy on the earth’s surface from the moon (per square meter) is only about a thousandth of a watt. To generate 1 watt of electricity from moonlight would require about 3,200 square meters of solar panels. But we can still see the moon perfectly well, can’t we?

As I proved to myself today, a signal can travel from North Carolina to Switzerland using substantially less energy than the energy produced by a candle. Beacons I transmitted today using less than 2 watts of power were heard in Switzerland, the Netherlands, England, Italy, and, of course, California. One of the reasons this is possible is because I used a digital, computer-generated mode of data communication that is extremely slow, efficient, and noise resistant. This mode is called “WSPR,” pronounced “whisper.” It takes almost 2 minutes to transmit this much text in the beacon: “K9WQ EM86wk 30.” The first four characters, K9WQ, are my FCC call sign. “EM96wk” is shorthand for my approximate location. The “30” is the amount of power I used, represented as decibels, and equals less than 2 watts.

That seems like magic to me.

I wanted to calculate how many watts of energy are in the sound of a human being shouting. I don’t quite know how to do that calculation, but I’m sure that plenty of people can shout louder than 2 watts. That’s one of the reasons I don’t watch television. I’d rather whisper on the radio.

Who I heard, and who heard me

One Comment

  1. David L.M. Marcum wrote:

    Today I read an article in a magazine I was about to discard, and immediately thought of you. In the Science & Technology section of the January 29-February 4, 2011 issue of The Economist (pp. 78 & 79), there is a fascinating article about the U.S. Navy’s development and successful testing of a communications antenna that is composed of a column of salt water jetted through a simple donut-shaped electrical coil attached to a radio’s antenna jack. The thickness of the water column determines bandwidth. The height determines frequency. And the salt water can be re-used by encasing it in a plastic tube. Utterly amazing.

    If you cannot find the article on-line, please let me know and I will scan it to you.


    Sunday, February 20, 2011 at 12:00 am | Permalink

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