Lou Posted - 5 September 2003 16:38 "Also, I came across this statement on the web. I am wondering if the portion which says that a mirror image of the radio wave travels BENEATH THE SURFACE OF THE EARTH is wholly true,

"Technical Note: Radio signals (waves) such as we encounter in the am radio band have two halves. One half travels across the surface of the earth at the speed of light through people, buildings and other objects.

The other half, a mirror image, travels beneath the surface of the earth. This radio wave has a definite length. Its length is the speed of light divided by the frequency. For frequencies in the megahertz region this approximates to 300 divided by the frequency in megahertz."

Here is the entire link:

http://my.integritynet.com.au/purdic/crystal_set.htm"


sky Posted - 5 September 2003 18:14 " The notion of a mirror image of the electromagnetic wave traveling through the earth below the soil surface is a falacy.

The mirror image refers only to the broadcast antenna having a mirror image. What this means in practical terms is that a resonant antenna would only need to be 1/2 the hieght.

The electromagnetic wave has finite energy and the energy it contains is diminished by square law due to the spreading of the wave. The energy is also absorbed by nearly everything in the path of the wave both natural and man made. The largest portion of the wave's energy is absorbed by the soil as the wave passes over and charges the soil surface. The energy is absorbed as heat.

When an electromagnetic wave induces currents into an antenna those same currents re radiate a substantial portion of the wave back into the air. This is called the antenna radiation resistance.

Now in answer to your initial question. Back in the 1920's there was considerable research done in this area and one of the scientivic papers presented was the summerfeld analysis.
This paper goes into considerable detail of the properties of wave propogation. You can probably look this up on the web.

Be warned that the worst sources of radio information are common text books. Often the information is condensed for simplicity which can be misleading at best."

re's sky.

...Those were taken from a radio group I'm a member of. Some of these folks have been building and studying this stuff since they were kids in the 40's. If anyone is interested I can post the link.

Anyway thinks for the welcome. The reason for not responding till now was a much needed mini vacation... I check back later.
73's