Cooperative Measurements of Radio Fading in 1925 Page: 419
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COOPERATIVE MEASUREMENTS OF RADIO FADING IN
By J. H. Dellinger, C. B. Jolliffe, and T. Parkinson
At the beginning of 1925 the bureau invited a number of laboratories to
participate in the beginning of a cooperative program of measurement. During
the year the work was largely confined to measurements of fading at frequencies
within the broadcast band. The general plan of the work was the arrangement
of special transmissions in which a station transmitted; continuously during a
specified period while the observing laboratories made graphic records simul-
taneously. The observing method was that of Pickard, described in his paper,
"Short-period variations in radio reception," published in the Proceedings of
the Institute of Radio Engineers, volume 12, page 119, 1924. Twenty-three
laboratories engaged in this work.
The series of measurements on fading were devoted to studies of fading effects
during the.sunset period, effects during the solar eclipse of January 24, the
fading variations throughout a 24-hour day, and the effects of high transmitting
power on fading. For these tests special transmissions were made by broad-
casting stations WGY and KDKA.
The results of 150 graphic fading records made by the cooperating observers
established definitely a number of facts about fading that had been only sur-
mised or guessed previously. In addition, a number. of new facts about fading
and other vagaries of radio waves were brought to light. Fading is at its worst
about 60 to 125 miles from a broadcasting station; for greater distances it dimin-
ishes, but then increases again with distance, and has repeated maxima and
minima for greater distances. There are two readily distinguishable kinds of
fading, a fairly slow and a relatively rapid fluctuation.
This work led to the discovery of a highly regular kind of :fading which some-
times occurs during the 45 minutes just following sunset. This is evidently
due to an interference phenomenon, and its period shows a correlation with the
distance between the transmitting and receiving points.
I. Introduction---- ----------- ------------------------- --- 420
II. Status of knowledge of fading ...... .. 421
III. Apparatus and methods of measurement--. . _.---- . . 423
IV. Radio phenomena during solar eclipse-_ 7.. .. . . 425
V. Sunset fading tests_ ----- --. . ... - 427
VI. Special periodic type of fading . . - ----- 437
VII. Twenty-four-hour fading test ..... --- - -, . . 440
VIII. Effect of high power on fading--________ --, ._, _- ,:,,. 441
IX. Intensity and fluctuation as functions of distance- --- - - - - :443
X. Conclusions-, .=----T - ---== .-.. .._._. 447
XI. Acknowledgments -------------- --- ---------- 449
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Dellinger, J. H.; Jolliffe, C. B. & Parkinson, T. Cooperative Measurements of Radio Fading in 1925, report, August 17, 1927; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc66491/m1/3/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.