NDLI: Beyond-the-horizon point-to-point UHF radio systems

Content Provider	IEEE Xplore Digital Library
Author	Morrow Jr., W.
Copyright Year	1966
Description	Author affiliation: MIT, Lexington, MA, USA (Morrow, W., Jr.)
Abstract	Propagation measurements made in recent years have indicated that the attenuation of UHF signals transmitted over beyond-the-horizon distances is substantially less than that predicted by diffraction theory. The observed signal levels are generally attributed to scattering or partial reflection from non-uniformities in the troposphere or lower atmosphere, Average losses in excess of free space of the order of 70 db are observed at distances of 200 miles beyond the horizon. Due to changes in the troposphere, the median received signals undergo variations about the average value of as great as\pm 20db. In addition, severe rapid fading is usually present. Apparently modulation bandwidths of as great as one megacycle can be transmitted using antenna beamwidths of a few degrees. In order to overcome the large propagation losses, high gain antennas, high power transmitters, and sensitive receivers are used. Parabolic reflector antennas as large as 60 feet in diameter are employed together with high power klystron transmitters of up to 10 kw power output. Frequency modulation techniques similar to those employed in line-of-sight systems are common. The receivers use low noise-figure pre-amplifiers and wide-band fast acting limiter-discriminator circuits for operation with the weak received signals. To reduce the effects of the rapid fading, space diversity reception with either switching or combining of the receiver output signals is usually employed. Using these techniques, multichannel UHF communication systems have been designed for operation with as many as 60 voice channels over distances as great as 200 miles beyond the horizon with long-term reliabilities of 99.9% or more. The research reported in this paper was supported jointly by the Department of the Army, the Department of the Navy, and the Department of the Air Force under Air Force Contract No. AF 19
Starting Page	56
Ending Page	57
File Size	162061
Page Count	2
File Format	PDF
DOI	10.1109/IRECON.1955.1150311
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	1966-03-21
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Fading Atmospheric measurements Transmitting antennas Radio transmitters Diversity reception Terrestrial atmosphere UHF measurements Attenuation measurement Antennas and propagation UHF propagation
Content Type	Text
Resource Type	Article

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UHF Long-Range Communication Systems

Measurements of correlation, height gain, and path antenna gain at 1046 megacycles on spaced antennas far beyond the radio horizon

Results of Propagation Tests at 505 mc and 4,090 mc on Beyond-Horizon Paths

Multipath fading measurement and prediction on 10 GHz fixed terrestrial link

Correspondence

Relationship between cross-path winds and fading rates in microwave propagation beyond the horizon

Sensitivity Of Troposcatter Communications To The Resolution Of Radiosonde Data

Human detection system using UHF band terrestrial TV receiving waves

Some Tropospheric Scatter Propagation Measurements near the Radio Horizon

Beyond-the-horizon point-to-point UHF radio systems

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UHF Long-Range Communication Systems

Measurements of correlation, height gain, and path antenna gain at 1046 megacycles on spaced antennas far beyond the radio horizon

Results of Propagation Tests at 505 mc and 4,090 mc on Beyond-Horizon Paths

Multipath fading measurement and prediction on 10 GHz fixed terrestrial link

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Relationship between cross-path winds and fading rates in microwave propagation beyond the horizon

Sensitivity Of Troposcatter Communications To The Resolution Of Radiosonde Data

Human detection system using UHF band terrestrial TV receiving waves

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