At radio frequencies you will seldom encounter true reflections. By true reflections I refer to situations where the signal bounces off of an object like a beam of light bounces off of a mirror. It can happen when the object is rather large compared to the wavelength, and has a surface that has only holes or changes of contour that are small compared to the wavelength. The side of a large metal sided building, like a hanger or industrial building with few or no windows or doors would produce reflections.
The more usual situation is scattering of radio energy. This is analogous to a broad beam of light hitting a stucco wall. The light scatters in all directions, so the area illuminated on the wall can be seen from any location with a clear view of the spot. The radio signal hits a mountain, hill, or building with a complex surface, and signal scatters from it in many directions.
This is a term borrowed from optics. It refers to an effect as a light beam passes across the edge of a sharp object like a knife blade. On the side of the blade away from the light source, light bends downward into the "shadow" area. The sharper that bend angle, the less the light intensity. The percentage of energy bent in this fashion is very small. An important parameter is the width of the edge of the knife blade in relation to the wavelength of the light.
The same thing can happen at VHF radio frequency. (Remember, radio and light are exactly the same physical phenomenon; the only difference is the frequency.) Because the wavelength is so much longer than light, the sharp ridge of a hill can act as the "knife" blade.
We actually made use of this effect on one hunt where we were hiding. (See the article, "Dirty Tricks," the section on Knife Edge.
Generally, this effect has very little importance because the amount of energy bent is so very tiny. It is included here primarily for completeness.
George Russ Andrews
President
George R. Andrews (Russ, K6BMG)
BMG Engineering, Inc.
9935 Garibaldi Avenue
Temple City, CA
91780, USA
Voice 1(626)285-6963
Fax 1(626)285-1684 (24 hour automatic)
America OnLine: Grandrews
Web: http://members.aol.com/bmgenginc
(7 Feb 1996)
Send E-mail to grandrews@aol.com.
(A message window will open.)
Return to This article,
Contents.
Go to Next Page of this
article.
Go to Prior Page of this
article.
Return to TOP PAGE.