Early Electromagnetic Research
In 1843 Faraday began intensive research into whether space could conduct electricity. In April,1846 he reported his findings in a speech called "Thoughts on Ray-vibrations." He continued work in this area for many years, with inventors and academicians closely following his discoveries and theories. James Clerk Maxwell, whom we today would call a theoretical physicist, pondered constantly over Faraday's findings, translating and interpreting these field results into a set of mathematical equations. Maxwell often wove these equations into the many papers he published on electricity and magnetism. Scientists knew that light was a wave but they didn't know what made it up. Maxwell figured it out.
In 1864 Maxwell released his paper "Dynamical Theory of the Electromagnetic Field" which concluded that light, electricity, and magnetism, were all related, all worked hand in hand, and that these electromagnetic phenomena all traveled in waves. As he put it "[W]e have strong reason to conclude that light itself -- including radiant heat, and other radiations if any -- is an electromagnetic disturbance in the form of waves . . ." Maxwell found further. If electricity rapidly varied in amount then electromagnetic waves could be produced at will; they would radiate in waves to a distant point. At least he said so. There was no method yet to prove that "other radiations" existed, to demonstrate that waves other than light occurred. How could one see, produce, or detect an invisible wave?
Visible light is only one small part of the omnipresent electromagnetic field or spectrum, that great, universal energy force that constantly washes over and through us. (Illustration, 244K) All matter is in fact a wave (internal link) Radio waves as well as infrared waves lie below the visible spectrum. Things like X-Rays lie above. And because light is a radiated electromagnetic emission, lasers and all things optical qualify, strictly speaking, as a radio transmission.
Maxwell's equations also stated that radiation increased dramatically with frequency, that is, many more radio waves are generated at high frequencies than low, given the same amount of power. Experimenting with generating high frequency waves thus began. This wasn't an easy task since it isn't until 90,000 cycles per second, or 9kHz, that radio begins. The familiar A.M. radio band starts around 560 kHz, or 560,000 cycles a second, with all present day radio-telephone services far, far above this. If you want to define radio, generating a rapidly oscillating, high frequency electromagnetic wave is certainly a prerequisite.
Radio spectrum not to scale, Diagram above modified from here: http://www.jsc.mil/images/speccht.jpg (519K) external link)
Need a different perspective on the spectrum? I have archived a nice NASA diagram. Click here (internal link)
Got Java enabled in your browser? Most folks do. Then try this URL for an excellent demonstration of an electromagnetic wave, it correctly portrays how electric and magnetic fields travel at right angles to each other:
http://micro.magnet.fsu.edu/primer/java/electromagnetic/index.html
Blue stands for the electric field and red for the magnetic field. An electrical current or signal always has a magnetic field associated with it, either in a wire or out in space when it is radiated from an antenna. This modulated signal does NOT go straight up, rather, these big and small loops of electrical energy, depending on how low or high the frequency, are whipped out 360 degrees from an omnidirectional antenna such as the one above. Or focused like a light beam from a directional antenna.
Let's review before we look at how early radio developers developed high frequency waves. At the top of this page we saw how Morse used conduction, to wirelessly pass a signal without using the atmosphere. The second way is to do wireless is by induction, where one wire induces current to flow in another. The third way is radiation, where high frequency, rapidly moving waves get generated by electricity and radiate from a fixed point like an antenna. I want to cover induction just a bit more, to better let us understand the difference between this method and what we now know as true radio.
Don't be put off with phrases like "lines of force" and "electro-magnetic fields." The above is a simple bar magnet with its lines of force. Wrap some wire around it, connect the wire to a battery and you will have an electromagnetic field. Communications often use complex words for simple subjects. For an excellent, authoratative look at electricity and magnetism, visit the IEEE site below:
http://www.ieee.org/organizations/history_center/general_info/lines_menu.html#eandm