The atmostphere is the antenna!

This may be a wild goose chase. Researchers at Samsung in Korea are now working on a way to turn the ionosphere into an antenna. A patent application filed by the company reveals plans to direct higher frequencies radio signals, at about 1 gigahertz, at the ionosphere, to alter its behavior. Is it possible? Maybe. In 2006 they filed a patent. It's inventor is listed as Sang-Hun Lee. The abstract reads as follows:

"Disclosed is a long distance communication system using the ionosphere. The long distance communication system includes an Earth station for modulating a signal having a modulation frequency onto a carrier frequency signal, which is absorbable in the ionosphere, and radiating a modulation frequency signal to a specific region of the ionosphere. The signal transmitted from the Earth station converts a DC current into an AC current in the ionosphere and the AC current re-radiates the modulation frequency signal to the Earth. "

It regards use of a portion of the ionosphere as an antenna. As a refresher please recall that the ionosphere is the layer of the atmosphere at an altitude of 50 kilometers. We already use thsi layer to bounce low frequency radio signals from one side of the world to the other. This is not what the patent is covering.

It describes a long-distance communications system using an Ultra High Frequency (UHF) radio signal with a carrier frequency below 2 GHz. This signal is to be transmitted from the Earth to the ionosphere which will accumulated energy. This will change electron temperature thus causing DC current to converted into the AC current. This AC current is to be modulated by controlling the change in electron temperature. This point of reflection could then operate as an antenna re-radiating the UHF signal back down to Earth.

I have come to think that this may be a bogus patent. The Serial number and the Application data all lead to one US patent # 6904080. It's abstract is as follows:

"A receiving circuit has a speech/no-speech signal detector for detecting whether there is a speech signal or not based on data inversely diffused by finger receivers, and a clock controller for controlling operation of the finger receivers based on a detected result from the speech/no-speech signal detector. If a speech signal is detected by the speech/no-speech signal detector, then the clock controller controls all the finger receivers to operate. If no speech signal is detected by the speech/no-speech signal detector, then the clock controller controls only one or two of the finger receivers to operate."

The details of that significantly different sounding patent regard CDMA which is completely different than all I described previously. Was it all a hoodwink? Maybe so.

Radio in Tunnels

You drive through a tunnel, you lose your station. With AM signals the effect is much more pronounced, but an FM can blink out as well depending on tunnel length and location. Some press in 2005 claimed that IBOC for AM would solve "through tunnel fade-out." It won't. To be fair, I should also state that satellite radio fades out too. Physics is a bummer.
Think of water, a wave of water. When moving water encounters an obstacle, it continues to move straight ahead, but it also bends. Radio waves bend a little into the tunnel. This is why it fades out instead of blinking off. In addition to that the demodulation of the signal may become impossible as is weakens.

In an FM signal silence usually means pristine reception but a carrier wave with no data. In absence of an FM signal, indigenous RF noise is demodulated and we call this wonderful noise static. So in the tunnel when you hear silence that's because your radio can detect "no signal" unambiguously and it's AGC (automatic gain control) can clamp down the volume automatically to spare you the noise. These radios "lock" on a signal and adjust volume to improve the listening experience. But the amplifier itself generates some noise so actual silence is difficult to achieve.

In the 1970s a lot of study went into this arena. Coal companies found themselves forced to add safety features to mines to protect the lives of miners. Then President Jimmy Carter signed a set of mine safety laws spurring the U.S. bureau of mines crack down. They got busy making standards, requirements for permits, gear and communications. More here. Transmitting UHF waves in coal mines was difficult despite the fact that the waves were smaller than the tunnel dimensions. Any part of the wave that impinges on the surfaces of the tunnel is refracted back away from the wave guide and represents a power loss.

It's easier to fix the tunnel than the radio. Any short tunnel can be wired for AM and or FM broadcast by feeding a broad-band amplifier into a leaky transmission line. The leaky transmission line will need to be run into or even through the tunnel depending on it's length.

A leaky transmission line is just a single length of wire or flashing running near the ceiling. In this scenario the ceiling and the line are both conductors in an electric circuit. But concrete and rock are conductors. It's an inefficient configuration but simple in design and easy to execute. The "broad-band amplifier" is more complicated than it sounds. Amplifying all frequencies is very difficult. in application we use an amplifier in as narrow a range as possible. Typically separate amplifiers for AM FM and cell. In sum, the problem is not unsolvable, just not cost effective to correct, so it is likely that things will proceed as is.