A violent storm erupted here in the mid-waste, I mean, mid-west, last night, causing me to shut down KDX radio for protection from power interruptions. Tornado sirens had me positioned in the basement with emergency lighting handy, and a weather radio listening to NOAA at 162.550mHz. It was a good time for brain bending.
1. I wondered about antenna shape. The subject of fractal antennas has been well discussed and has to do with shaping an antenna. Here’s a good link
http://part15.us/node/2129
In some ways acoustics are comparable to electronics, e.g., speed of sound/light; resonant frequency; harmonics and overtones. So I thought of an interesting discovery of a few years ago I read about, regarding the shape of a bell. Traditional bells have a familiar flare-out-at-the bottom shape, which produces minor harmonics and over-tones, thus the “mournful” bell sound. But someone figured out that a bell flaring IN at the bottom produces MAJOR harmonics and overtones! A significant acoustic finding. Maybe a bell shaped antenna?
The only clue I can think of as to “what electricity looks like” is lightning, and that shape is always a fractal one, which brings us back to that.
2. In music it’s the harmonics and overtones that give each instrument its distinctive rich characteristic and therefore “high-fidelity” demands preservation of the wide-spectrum harmonics. But the opposite applies in radio transmission, where we only use the fundamental frequency and try to smother the uppers. BUT, imagine, say, a transmitter with the fundamental at 600kHz and a perfect well tuned 2nd-harmonic at 1200kHz, wouldn’t it be neat if entirely different programming could be modulated on each of the two carriers? Impossible? I wonder.
Be Careful!
All those harmonics may cause planes to crash…
TSA Scan Time
A harmonics scan or, opting out, a harmonics pat down.
Safe skies.
Impedance & Modulation are the Keys…
Carl…interesting thought. Put down the ganga and let’s think this through. Fresh air and daylight usually helps.
1. Radio antennas, in and of themselves, do not generate radio signals on their own. They can, however, attenuate and accentuate various harmonic-rich broad spectrum signals. Because an antenna is an electronic component, albeit a passive one, its inherent reactant produces these affects with some predictability. That is why fractal antennas have been of some interest; multiple signals through a common radiator (wide bandwidth). So, a bell-shaped antenna would have a specific reactance (Xl or Xc) and resistance (R) at a particular frequency causing it to react to a generated signal from a transmitter in a predictable manner X + R = impedance @ frequency. The impedance shift could be such at the harmonic to almost obliterate the harmonic signal level. We usually call this a filter. This is over simplified for the purposes of this forum.
2. Since information is imposed upon the radio signal as modulation (amplitude, frequency, spread spectrum, etc.) of the main carrier signal, how would this information be removed or added to the second or subsequent harmonic, separate from the main? How would the characteristics of a clean main signal be restored to the harmonic signal?
The second harmonic would have to be able to be modulated independent of the main carrier modulation. Two sets of digital pulses could be generated on the main carrier and the different digital strings could be filtered and decoded (recognized and/or ignored) in separate receivers set to the different frequencies. One on the main carrier, and another on the harmonic. That is a lot of work for very little return. The use of sidebands and sub-carriers would be a different scheme altogether. Even a CW code signal would not work with a different message on the main and harmonics. In short, maybe it could be done, but I can’t visualize how it could be done economically or efficiently.
I have it by good authority that the mother ship will be arriving soon. So, hang in there.
Moving On
Mr. Johnson, Sr. said, regarding the idea of individuating the first two harmonics of a transmission…
“In short, maybe it could be done, but I can’t visualize how it could be done economically or efficiently.”
Well, that’s the story of part 15 low power radio.
And I don’t know about the mothership, except that it transmits at a frequency of .01 Hz.
Back to the subject of fractal antenna, basically a tree formation is an example of a fractal pattern, and no two trees (in nature) are exactly alike. Probably in human production a fractal product would have a uniform design, but still, it would necessarily look like a small tree if built on a scale confined to the 3-meter part 15 length-limit. It would be like a fruit tree.
An actual tree has a somewhat mirror-like root-base (the bottom of the tree mirrors the top) located below ground, and perhaps this tells us to try fractal grounding designs.
A good knowledge of metal-smithing would help.
Even if a 3-meter high metal tree were built, a new FCC issue would arise in the fact that measuring the length of each branch and each twig might total up to a hundred meters, so now we could argue that a truly compliant part 15 fractal antenna would be the size of a pygmy bush.
Continuing
A fractal object in the natural world (tree, lightning) is of course three-dimensional, but the human mind has two qualities (distortion and invention or both) which make it possible to imagine a 2-dimensional fractal pattern, something only found in nature if crushed under a flat rock, but there are very few flat rocks.
Anyway, in my fractal experiments I intend to try both 3-D and 2-D fractal antennas, never more than 3-meters tall. The metal work will probably require welding unless you can suggest a way of building metal fractals that will hold their shape without welding.
The simple guiding principle in composing a fractal without bothering with mathematics is to extend a branch into any nearby unoccupied space.
You know, a 2-D branching fractal ground plane would be an interesting alternative to a standard radial pattern.
The Antenna Was The Transmitter!
I remember reading some history about very early radio experiments. One interesting “system” consisted of two kites on opposite sides of a valley, each tethered by metal cable which acted as an antenna.
The tethers were of the same length (read wavelength.) As static electricity built up on the tether, at some point a fair electrical charge existed.
When the charge was manually caused to quickly discharge, the result was a discernable signal received by the other kite operator. I don’t remember if the “signal” resulted in an audible click or a spark but the results could be repeated over and over. Hence, intelligence could be transmitted wirelessly.
Essentially with nothing more than an antenna, a radio signal was generated and received at a remote point. This would have been a damped wave but at a specific frequency determined by the antenna.