This is the Jurassic Radio Section of
The Broadcast Archive
Barry Mishkind - The Eclectic Engineer
Telecommunications, Part V
This is the fifth in a series titled Jurassic
Telecommunications describing the late Victorian, non-electronic roots of modern
telecommunications. Although the operational technologies have changed, the core
technology and simple principles behind it have not. Most technology history
fails to adequately chronicle those simple early methods and the gargantuan
machines their developers often had to utilize.
RF Generators - Literally
By Donald E. Kimberlin, NCE
June 13, 2000
Many telecommunications textbooks lead with a statement that
electrical communications involves transmitting power from one point to another.
That, of course, is what makes electric telecommunications a branch of the
broader art of electrical engineering. Recurrent revolutions have occurred,
however, reducing the amount of power needed to signal electrically between two
places, such that today numerous flea-powered transmitters surround our daily
Radical developments in receiver sensitivity and selectivity,
transmitter encoding, and stability of RF circuitry have made it possible for
untold quantities of RF generators to occupy and re-use the same spectrum space
over and over.
Figure 1 - Alexanderson
17.2 kHz 200 kW alternator at RCA station, Grimeton, Sweden
It didnít start out that way
The very first "wireless"
transmitters were, of course, little more than controlled lightning bolts. At
the outset, when there was essentially nobody else on the entire spectrum,
splattering out a wide signal rife with harmonics mattered little. The simple
accomplishment of receiving something from which intelligent information could
be recovered was the miracle in itself. The frequency of radiated signals was so
low that even antennas miles long were grossly inefficient, and what with no
amplification in the first receivers, the only means to succeed was to stimulate
the Earthís magnetic field with brute force.
Indeed, a report in the time-honored journal Scientific
American describing Marconiís 300 kilowatt transatlantic arc transmitter
at Clifden, Ireland included night photos. These showed how its antenna wires
radiated ultraviolet light which caused glowing streaks invisible to the naked
eye. The mind boggles at what environmentalists would say about such a machine
Effect" and the early age of wireless
As early as 1897, Adolph Slaby had begun
efforts to narrow transmission bandwidth of Marconiís transmitters, starting
Marconiís use of the principle of "syntony" described by Oliver
Lodge. What resulted was "narrowband" in the loosest sense of the
word, however. For the first few years, radio operators had to make use of the
psychological phenomenon known as the "cocktail party effect,"
focusing their hearing on the character of scratchy tones from the station they
wished to copy, ignoring all others.
Even though Marconi began to suggest syntony was essential to
shared use of the ether, it was others who made greater strides in finding ways
to share than he. Germans made much early progress in this aspect of the early
art of "wireless."
Among those efforts were some unique German
approaches to generating "continuous waves" by building actual
Where Fessenden in the U.S. had Ernst
Alexanderson working on making alternators that ran at higher and higher
frequencies, the European view was to create means of frequency multiplication.
On this front, Slabyís assistant, Count von
Arco, created an early alternator that eventually became the transmitter of the
ill-famed Sayville, New York Telefunken station.
It was the transmitter used to relay the
infamous "Zimmerman telegram" and the message to U-boats telling them
to sink the Lusitania. Those two messages played a major part toward dragging a
recalcitrant United States into a European World War.
Where Alexandersonís alternator directly
generated 60 kilohertz or more, the Joly-Arco alternator at Sayville operated at
only 9,613 Hertz, feeding its output into a static frequency converter (a
special type of tuned transformer) that resulted in a doubling of the pulse
frequency to 19,266 Hertz.
Its output then passed into a second static
converter which again doubled the frequency to 38, 452 Hertz. This carrier
frequency of 38.5 kilohertz made the Sayville station one of the higher
frequencies on the air at a time when most of the world operated at less than 20
kilohertz. Its much shorter wavelength made for considerably higher antenna
efficiency than others, while Its low machine rotational speed and relatively
high overall power efficiency of about 60% at an output power of 100 kilowatts
created power to light a small town in that early era of primarily light bulbs
as power consumers.
The Goldschmidt Alternator
At a second Telefunken installation at Brunswick, New Jersey,
another German development was used. This one, a Goldschmidt alternator,
contained the static frequency converters built right into the field windings of
the huge machine itself. The Goldschmidt machineís frequency multipliers
functioned in a reentrant additive way to initially generate 15,000 Hertz, then
add to itself achieving 30,000 Hertz. It then added twice again to result in a
second intermediate frequency of 45,000 Hertz and an output of 60,000 Hertz.
This put Brunswick near the upper limit of transmitter
technology of the day, in the region where Fessenden had operated a voice
alternator in 1906.
The Brunswick machineís 200 kilowatt output at this even
higher carrier frequency was said to have an overall power efficiency of 80%,
giving its own claim to improved technology. This claim did bear the expense of
extremely tight mechanical and electrical tolerances in operation, however. If
even small errors occurred in phasing the reentrant harmonics, eddy current
heating caused the armature to rub and scrape on the frame, causing severe
damage to the alternator.
Figure 2 - 200 kW 60 kHz Goldschmidt Alternator
at New Brunswick, NJ
Yet a further German development was constructed at the Nauen,
Germany Telefunken plant, simply called a Schmidt alternator. This was a
500-kilowatt monster that generated only 6,000 Hertz, but used a huge resonant
tank circuit to directly couple a 24,000 Hertz output to its antenna. Its power
efficiency was a relatively low 60%, but its huge power output was its claim to
fame, being used to reach as far as Argentina from Germany on a regular
Radio began in France in 1897 with early work
by military officers Ducretet and Ferrie. By July, 1919, PTT engineer Maurice
LaTour installed a Gallic variation on alternator technology that ran several
rotating elements on a single shaft to produce higher power levels than did
Alexandersonís in America.
Figure 3 - La Tour - Bethenod
Alternator at Doua near Lyon. Note man at switchboard; another at right side end
The French PTT used the LaTour-Bethenod
machine for several decades. Even as late as 1942, its German captors used this
machine for communication to submarines. Its rotational speed was a relatively
low 3,000 rpm while producing a radio output of 20,000 Hertz. Today, much of
that machine is on display at the Musee Ampere at Poleymieux.
The Passing of the Age of
The grandest plan of the Age of Alternators
was put forth at the inception of RCA, which at first intended to build a
monstrous plant of six 200 kilowatt Alexanderson alternators at Rocky Point on
Long Island. The intent was to be able to reach any point on the globe via a
low-frequency transmitter. The plan was never completed, however, when HF radio
came to the fore and supplanted the LF machines. Today, one remaining
Alexanderson dinosaur lives at Grimeton, near Goteborg, Sweden, where the RCA
station in Alexandersonís home nation is maintained in mint condition as a
national museum of technology, complete with its six 500 foot antenna towers. A
dedicated crew of enthusiasts airs it on 17.2 kHz for special occasions related
to radio history.
Want to know more? Here are some websites with
information on alternator transmitters:
Sayville and German Pumps - http://www.asb.com/usr/w2g3zfj/about.htm
Slaby biography - http://www.cinemedia.net/SFCV-RMIT-Annex/rnaughton/SLABY_BIO.html
1914 Goldschmidt Alternator Article -http://home.luna.nl/~arjan-muil/radio/alternator.html
Lyon_LaDoua, France PTT radio -http://pascalsimeon.free.fr/radioly.htm
Early Wireless Telegraphy -http://pascalsimeon.free.fr/tsf.htm
Grimeton Radio Station, Sweden -http://www.telemuseum.se/Grimeton/defaulte.html
has written many articles about his experiences over the years, as well as those
who were the pioneers in the telecommunications and broadcast industries.