Cooperative Measurements of Radio Fading in 1925 Page: 420
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Scientific Papers of the Bureau of Standards
This is the third extensive program of cooperative radio-wave-
phenomena observations conducted by the Bureau of Standards at
frequencies within and above the broadcast range. The first two of
these were qualitative investigations carried on with the cooperation
of several hundred amateurs in 1920-21 and 1922-1924,2 being,
respectively, on radio-signal fading and on the conditions affecting
distance range of broadcasting. In 1924 methods came into rather
general use for making quantitative measurements of the various
transmission phenomena. At the beginning of 1925 the bureau
invited a number of laboratories to participate in the beginning of a
cooperative program of measurements.
The several quantities meriting cooperative study on a large
scale include: Field intensity, fading, direction variations, polar-
ization, and atmospherics. In 1925 the work was largely confined
to measurements of fading. This quantity was selected because
fading phenomena give a particularly promising means of studying
the wave characteristics, and also because the apparatus required
is relatively simple. The work was mainly at the broadcast fre-
quencies, because transmissions with uninterrupted carrier wave
are not so commonly available in other parts of the frequency spec-
trum. Results at other than broadcast frequencies and direction
observations, where mentioned herein, are therefore considered as
incidental to the principal aim of the 1925 work, which was the
study of fading phenomena in the broadcast range.
The work was done by the aid of special transmissions from a
broadcasting station during which the observing laboratories made
graphic records. The observing method was that described by
Pickard.. Mr. Pickard participated in the 1925 program and placed
his experience and skill fully at the disposal of the bureau and other
Twenty-three laboratories were engaged in this work. Their
names are listed at the end of this paper. Figure 1 shows the geo-
graphical distribution. About 20 other laboratories expressed inter-
est in the work and made some effort to begin observations, but the
ones listed are the only ones that completed observations and sent
them in. The results of some of the tests have been described in
part in special reports that some of the cooperating observers have
published. A preliminary paper on the work as a whole was pre-
1 B. S. Sci. Paper No. 476, Radio Signal Fading Phenomena. J. H. Dellinger ,and L. E. Whittemore,
J. Wash. Acad. Sci., 11, p. 245; 1921.
' B. S. Tech. Paper No. 297, A Statistical Study of Conditions Affecting the Distance Range of Radio
Telephone Broadcasting Stations, C. M. Jansky, Jr.
3 " Short-period variations in radio reception," G. W. Pickard, Proc. I. R. E., 12, p. 119; 1924.
t vol. 2
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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/m1/4/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.