September 1956 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Early investigations into RF signal atmospheric
'ducting' was reported in this 1956-era article in Popular Electronics. Ducting effects
were first noticed during World War II when Nazi broadcasts from occupied Paris were received occasionally
in London. Scientists discovered that a small change in the humidity of the air near the surface has
the effect of trapping radio waves, a trapping process dubbed "ducting." These waves are conducted as
if they were inside of a metallic waveguide. Research by the U.S. Army Signal Corps determined a sudden
temperature rise of around 50 to 200 feet above the surface appears to have the strongest effect.
Army Studies Radio Wave Curvature
Weather tests are being conducted by Army to analyze effects
of temperature and humidity changes on microwave transmissions. At left, members of meteorological team
prepare "Kytoon" - a helium-filled nylon-covered balloon - for ascent.
The Army Signal Corps is carefully watching weather effects on microwaves with an eye towards "seeing"
beyond the horizon. Normally, microwaves - used by, u.h.f. TV stations - can only travel from transmitting
points to the horizon, or within line of sight. However, certain types of weather conditions trap these
radio waves and curve ,them around the horizon.
"Kytoon," carrying a "Wiresonde" which records temperature and humidity, rises in
front of 200' tower containing electronic equipment used to measure air conditions. This weather balloon
can go as high as 1500 feet.
Personnel of the Aviation and Meteorological Dept., Army Electronic Proving Ground, Fort Huachuca,
Arizona, are interested in determining the exact constitution of these unusual conditions. Electronic
measuring instruments have been developed that will detect minute changes in the temperature and humidity
of surrounding air.
Wind direction, velocity and humidity are checked on instruments located in base
of tower. Testing takes place at Gila Bend, Arizona.
Scientists have discovered that a small change in the humidity of the air near the surface has the
effect of trapping the radio wave. Microwaves caught by trapping are said to be "ducted" - or passed
along as if they were inside of a metallic wave guide. A sudden temperature rise some 50 to 200 feet
above the surface appears to have the strongest effect.
The Signal Corps needs to know the extent of these effects to judge whether or not microwave transmissions
can be intercepted by an enemy. During World War II ducting was suspected when TV pictures from the
Nazi-held transmitter in Paris could be seen across the English Channel - to the military advantage
of the British.
Posted March 13, 2015