Dec. 1931 / Jan. 1932 Short Wave Craft
Wax nostalgic about and learn from the history of early electronics. See articles
from Short Wave Craft,
published 1930 - 1936. All copyrights hereby acknowledged.
Prior to atmospheric sounding rockets and orbiting satellites, all
information gained and theories developed on the nature of Earth's
upper atmosphere and its interaction with electromagnetic waves
(radio in particular) were purely
academic, not the result of empirical data. That is not to say the
theories were wrong (although some were),
just that they were incomplete. For that matter, even today there
is still much to be learned and, according to an excellent article
in the October 2015 issue of the ARRL's QST magazine titled
Myths of Propagation Dispelled" (by Carl
there is still a lot of misinformation being believed and promulgated
about shortwaves and how they travel in the atmosphere. This work
(very much worth your time) is a great
testament to the level of expertise that exists in the realm of
Amateur Radio, and the contributions made by it to the science world.
The rest of this article appeared in the
February/March 1932 edition of Short Wave Craft.
How Are Shortwaves Propagated?*
By Ferdinand Bödigheimer
The author gives high credit to short wave amateurs who have
contributed greatly to the data here presented on short wave phenomena.
The question of whether short waves penetrate the Heaviside layer,
thus making possible radio communication with other planets, is
Fig. 1 - This diagram shows the direction of
maximum radiation from a vertical antenna excited by harmonics.
Before the extraordinary range of short waves was discovered
by amateurs, it was held as incontrovertible that the electric waves
followed the surface of the earth, and that the strength of the
field decreased in proportion to the distance. It was assumed as
simply natural without its causing any more surprise and attention,
that for communication at a very great distance only long waves
were serviceable, with the expenditure of correspondingly great
energies. Operation was carried on with wavelengths of 2 to 3 kilometers
(that is, with frequencies from 150,000 down to 100,000 cycles)
and with energies of many hundred kilowatts.
The shorter the wave, the less suitable it seemed for distant
communication. Waves of a few thousand meters were used in continental
communication, but not in transoceanic. Waves of about 1,000 meters
and less were intended for internal communication and for neighboring
states. Finally came the waves of 600 and 300 meters for communication
of ships with one another and with coast stations; that is, mostly
for very short distances.
Waves Below 300 Meters Were Considered Useless
Waves of less than 300 meters were considered entirely useless,
because they actually proved very unreliable in communication at
short distances; for which at any rate, they appeared in question.
It did not even cause thought that, during the war, weak German
ship and field stations in Turkey were occasionally heard on the
300-meter wave by crystal receivers located in Germany. Likewise,
the fact that the ships with their resounding transmitters disturbed
or drowned out the first 300-meter radio stations at night from
"impossibly" great distances, received no consideration. The fact
was established: waves of 300 meters and less are absorbed by the
influence of the sun's rays in their course along the surface of
the earth. That they were more serviceable at night and, under certain
circumstances, audible at very great distances, was attributed to
the absence of the solar radiation.
Fig. 2 - The radiation from a horizontal antenna
is evenly distributed over almost 180 degrees, as shown.
Amateurs Pioneers in Short Wave Work
Now, against considerable resistance, these views have fundamentally
changed. The pioneers of the new conception were the amateurs, who
even today have at their disposal the greatest experience and in
part stand preeminent in the clarifying of still doubtful problems.
Below is a brief outline of the now familiar laws for short waves,
which touch on the new problems of propagation foremost in interest.
The general laws here given rest on the personal investigations
of the writer in the years 1926 and 1927; but, with reference to
their general physical basis, on previously known facts or theories.
The special data regarding the influence of the weather are based
on independent researches performed by Dr. Karl Stoye and the writer,
who have had occasional interchanges of ideas. These investigations
are still going on.
Fig. 4 - Radiation at various frequencies, 1
to 4, some of which are partly bent downward, some passing through
the Heaviside layer with parallel deflection.
(1) The maximum radiation from a vertical antenna, especially
if it is stimulated by harmonics, projects obliquely upward at an
angle. (See Fig. 1.)
(2) A horizontal antenna radiates evenly, over an angle of nearly
180 degrees (Fig. 2),
(3) At a height of 50 to 100 kilometers (30 to 60 miles) above
the surface of the earth, there is, according to Heaviside's theory,
a stratum of atmosphere which, because of the sunlight and the electron
radiation of the sun, is distinguished by a very large number of
free negative electrons per unit of space and, because of the slight
atmospheric density, by a very great number of heavy ions or positive
particles. In view of the great open stretch, there takes place,
by impact ionization, a further increase in the number of free electrons.
The electron density gradually increases in a vertical direction
and again decreases. The dielectric constant of the Heaviside layer
is smallest where, in consequence of very great electron density,
the electrical conductivity of the layer is greatest. This gradual
change in the dielectric constant effects a refraction similar to
astronomical refraction (also analogous to the formation of the
"Fata Morgana" and mirages) and finally total reflection of the
electromagnetic radiation (see Fig. 3). The space radiation is thus
Fig. 3 - The space radiation is bent downward; more exactly it
is refracted and totally reflected (at certain frequencies).
Fig. 5 - Assumed diffusion of energy by strata
of high relative moisture; normal course of radiation in dotted
lines. For the sake of simplicity, a straight course of radiation
and reflection was drawn, instead of indicating refraction.
Ultra Short Waves Pierce Heaviside Layer
(4) The refraction is, as in the case of light, dependent on
the frequency. High frequencies (short waves) are less strongly
refracted than low frequencies (long waves). A pencil of electric
waves of different frequency, increasing from I-IV (cf. white light)
would behave as in Fig. 4. (This is similar to the production of
rainbow colors in the refraction of white light.) The range is smaller
in the case of long waves than in the case of short ones. Very high
frequencies (ultra-short waves) are no longer refracted, but pass,
with a parallel deflection, through the Heaviside layer; since,
in consequence of the slight refraction, the limiting angle for
total reflection is not reached. Rays striking the Heaviside layer
perpendicularly pass through it unrefracted.
(5) The energy of ground radiation, whose proportion of the total
radiation is great (especially with horizontal antennas ) is quickly
absorbed in consequence of the ion density being high near the ground,
and because of other sources of loss. On the contrary, the space
radiation moves along in the Heaviside layer almost without loss,
because of the slight ionic density.
(6) The absorption in consequence of the greater ionic density
near the ground is less, with high frequencies, than with the lower
ones. The fact that the ground wave is nevertheless (as a rule)
more quickly dissipated, with high frequencies, than with lower,
is attributable to other sources of loss.
The Cause of "Dead Zones"
(7) Since the ground radiation is used up after a few miles,
while the space radiation descends again to the earth only after
a greater distance, there results a silent zone, in which there
is no reception or only weak signals are heard.
(8) The height or make-up of the Heaviside layer, or perhaps
both factors, changes with the time of day and of year and with
the changing activity of the sun spots. Therefore these factors
have a great influence on the propagation of the short waves.
Best Frequency Varies With Seasons
With equal frequencies, the range is greater at night or in the
winter than by day or in the summer; hence, for example, for these
20 meters by day in the summer: European communication, by day
in the winter: DX (distance) communication;
40 meters by night in the summer: still European communication,
by night in the winter: DX (distance) communication;
80 meters by day in the summer: almost useless, by day in the
winter: places very near at hand; by night in the summer: European
communication, by night in the winter: also DX (distance) communication.
Fig. 6 - Vertical antenna (a) excited into harmonic
oscillation and horizontal antenna (b) with its characteristic radiation.
(9) The shorter the wave (the higher the frequency), the better
it is suited for communication by day and in the summer; but the
less it is suited for communication at night and in the winter.
(10) Ultra-short waves are not deflected downward; with regard
to their usefulness for communication, they behave almost like light
waves. (In so far as communication with other heavenly bodies might
be considered, then ultra-short waves would, be the most suitable.)
The limit between the ultra-short waves and those still serviceable
for "DX" (distance) is not sharp, but varies with the time of day
and of year. It lies at about 10 meters, as calculation and practical
experiments have shown. The present experiments with 10-meter waves
therefore lead toward "DX" communication in summer and by day, which
should be noted.
Condition of Atmosphere Affects Short Waves
(11) Considerable influence seems to be exerted according to
investigations not yet completed, by the weather or, more correctly,
the condition of the atmosphere at the edge of the stratosphere.
In fact, there evidently is a considerable significance in the "moisture
content" in the higher strata of air; shorter waves show themselves
most sensitive to these influences. The influence of the weather
is therefore stronger on 20-meter waves than on those of 40 or 80
(12) Uniformly dry air over transmitter and receiver seems to
be the best condition for good "DX" (distance) radiation (by day
there is strong interference by increased absorption).
(13) Meteorological conditions, and probably also the Heaviside
layer, are subject to marked changes (particularly the Heaviside
layer) at twilight, and at times of disturbances in the earth's
magnetism. The results are more or less rapid displacements of the
zones and, therefore, changes in signal strength. This gives an
explanation for "fading" which, according to the current explanation
that it is caused by the difference in phase between space wave
and ground wave, would be inexplicable in the case of short waves.
(14) At places in the middle of the zone of maximum sound intensity,
the power of the transmitter received plays a small part. With favorable
atmospheric conditions, one hears very slight energies (weak signals)
with the sound intensity R9.
(15) The form of antenna, vertical or horizontal, is of distinct
significance. From Fig. 6 it is evident that the horizontal antenna
is more favorable for close communication (Europe); the vertical
antenna, excited on a harmonic, is better for "DX" communication,
though to be sure over a relatively narrow zone.
(16) From the viewpoint of short waves, it is also possible for
us to look differently at long waves. Here too the ground wave is
far from playing the part still assigned to it today. It does not
reach far; with our chief German stations, in the autumn of 1930,
not even 200 kilometers (125 miles).
Reception improvement in the local zone is a question of the
antenna, likewise a question also of frequency! This effect should
be studied carefully by those who are seeking the salvation of long-wave
radio by utilizing tremendous transmitting powers. -Funk Bastler.
* The following is a section from the
book "Radioamateurstation für kurze Wellen," by F. Bödigheimer.
This should be of great interest to all short wave amateurs.
Posted October 26, 2015