by John S. Belrose
International Conference on 100 Years of Radio -- 5-7 September 1995
Many scientists and engineers have contributed to the early
development of electromagnetic theory, the invention of wireless signaling by radio,
and the development of antennas needed to transmit and receive the signals. These
include, Henry, Edison, Thomson, Tesla, Dolbear, Stone-Stone, Fessenden,
Alexanderson, de Forest and Armstrong in the United States; Hertz, Braun and Slaby in
Germany; Faraday, Maxwell, Heaviside, Crookes, Fitzgerald, Lodge, Jackson, Marconi
and Fleming in the UK; Branly in France; Popov in the USSR; Lorenz and Poulsen in
Denmark; Lorentz in Holland; and Righi in Italy. The inventor of wireless telegraphy,
that is messages as distinct from signals, is Italian-born Guglielmo Marconi, working
in England; and the inventor of wireless telephony is Canadian-born Reginald Aubrey
Fessenden, working in the United States.
According to Marconi, he was an amateur in radio: in fact this was
far from the truth. He foresaw the business side of wireless telegraphy. He was
aware, however, of his own limitations as a scientist and engineer, and so he
enlisted (in 1900) the help of university professor John Ambrose Fleming, as
scientific advisor to the Marconi Company; and he chose engineers of notably high
caliber, R.N. Vyvyan and others, to form the team with which he surrounded himself.
Marconi's systems were based on spark technology, and he persevered with spark until
about 1912. He saw no need for voice transmission. He felt that the Morse code was
adequate for communication between ships and across oceans. He was a pragmatist and
uninterested in scientific inquiry in a field where commercial viability was unknown.
He, among others, did not foresee the development of the radio and broadcasting
For these reasons Marconi left the early experimentation with
wireless telephony to others, Reginald Fessenden and Lee de Forest.
Fessenden was a radio scientist and an engineer, but he did not
confine his expertise to one discipline. He worked with equal facility in the
chemical, electrical, radio, metallurgical and mechanical fields. He recognized that
continuous wave transmission was required for speech and continued the work of Nikola
Tesla, John Stone-Stone, and Elihu Thomson on this subject. Fessenden also felt that
he could transmit and receive Morse code better by the continuous wave method than
with the spark apparatus that Marconi was using.
This paper overviews the differing technologies of Fessenden and
Marconi at the turn of the century, and their endeavours to achieve transatlantic
|Figure 1: Marconi's antenna system at Poldhu,
Cornwall, December 1901. (John
2. Transatlantic wireless communications began at
Heinrich Hertz's classical experiments were conducted in his
laboratory using a small end-loaded dipole driven by an induction coil and a spark
gap for his transmitter. His receiver was a small loop, and detection was by induced
sparking. Since the frequency generated by a spark transmitter is determined by the
resonant mean frequency of the antenna system, his experiments in 1887 were conducted
at VHF/UHF (60 to 500 Mhz) -- the corresponding wavelengths (5.0 to 0.6 metre) being
practical for indoor experiments.
Marconi started experimenting with Hertz's apparatus in 1894. He
was fascinated by the idea that by means of Hertzian waves it might be possible to
send telegraph signals, without wires, far enough for such a system to have
commercial value. By 1896 he achieved a transmission distance of 2.5 kilometres, by
using an earth and an elevated aerial at both transmitter and receiver (nowadays
called a Marconi antenna). His first permanent station established a link between the
Isle of Wight and Bournemouth, England, some 22 km away (in 1897). He established
communications across the Channel in 1899. By now he must have been using frequencies
in the low HF band, since his aerial systems were much larger.
In 1900 he decided to try and achieve transatlantic
communications. The required aerial size, and so the signalling frequency, at best
could only be projected by extrapolation from values successful over a range of much
shorter distances. The aerial at Poldhu, Cornwall in December 1901 (see Fig. 1), more
by circumstance than design (to be discussed), radiated signals in the MF band (about
Marconi kept building larger antenna systems, larger since he was
striving for greater transmission distance and improved signal reception, which
lowered the operating frequency. At Poldhu the frequency of his station in October
1902 was 272 kHz. His initial station at Table Head, Glace Bay, NS in December 1902
was a massive structure comprising 400 wires suspended from four 61 metre wooden
towers, with down leads brought together in an inverted cone at the point of entry
into the building. The frequency was 182 kHz. By 1904 his English antenna had become
a pyramidal monopole with umbrella wires, and the frequency was 70 kHz. In 1905 his
Canadian antenna, moved to Marconi Towers, Glace Bay was a capacitive top-loaded
structure, with 200 horizontal radial wires each 305 metres long, at a height of 55
metres, and the frequency was 82 kHz. By late in 1907 he was using a frequency of
Fessenden's early experiments using spark transmitters were
probably conducted at a frequency in the lower part of the HF band, since initially
he was testing over short links of a few kilometres using 50-metre masts to support
wire aerials. His belief was that radio transmission should be by way of continuous
waves (CW), not the damped-wave or whip-and-lash type of transmission provided by
spark-gap transmitters. The only way he knew to generate true CW was by a
high-frequency alternator, and in the period 1890-1905 10 kHz was the highest
frequency achieved using an HF alternator. But the efficiency of practical aerial
systems was very poor at such a low frequency. So he strove to increase the speed and
frequency of his HF alternator. In the meantime he invented the synchronous
rotary-spark-gap transmitter. His transatlantic experiments in 1906 were conducted
using such a transmitter and 420-foot umbrella top loaded antennas at Brant Rock, MA
and Machrihanish, Scotland, tuned to a frequency of about 80 kHz.
3. Marconi and Fessenden Their Differing
Marconi, those working with him, and most experimenters in the new
field of wireless communications at the turn of the century, were unanimous in their
view that a spark was essential for wireless, and he actively pursued this technology
from the beginning (in 1895) until about 1912.
Fessenden was a proponent of the continuous wave (CW) method of
wireless transmission. Somewhat alone in this direction in 1900-1906, his CW patents
had little impact on the users of radio technology. The golden age for spark was from
1900 to 1915; dominated by Marconi, who fought to quell any divergence from that
mode. The fact that the damped wave-coherer system could never be developed into a
practical operative telegraph system and that the sustained oscillation method should
be used was perceived by Fessenden in 1898 [see Electrical World, July 29, August 12,
September 16, 1899 and Proceedings American Institute of Electrical Engineers,
November, 1899, p. 635 and November 20, 1906, p. 7311. In 1900-1902 only two methods
were available for generating CW: 1) the HF alternator; and 2) the oscillating
Plain Aerial Apparatus
Marconi's early experiments employed plain aerial apparatus, and
placed the spark gap directly across the terminals of his vertical wire aerial-ground
antenna. His receiver employed a similar set-up, with a coherer type of detector. The
transmitter/receiver systems were untuned, excepting by the natural
amplitude-frequency response of the aerials. Unbeknownst to him his transmitter and
receiver were in effect "tuned" to different frequencies. The oscillating damped wave
on the transmitting aerial, which was in effect "connected" to ground through the low
resistance of the conducting spark, was in effect "tuned" to the fundamental quarter
wave resonant response of the aerial. His receiver however, awaiting reception of the
spark signal, would in effect be tuned to the half-wave resonant frequency of the
wire aerial -- since the coherer prior to the reception of the RF impulse-like signal
would present a high impedance between the aerial and ground.
This problem was solved by using a closed tuned circuit for the
receiver; and for the transmitter by using the circuit arrangement devised by Braun,
in which the oscillatory circuit (discharge capacitor and spark gap) was placed in a
separate primary circuit transformer-coupled to the antenna system. This latter
arrangement also lengthened the duration of the damped wave signal, since when the
spark ceased, the oscillation in the antenna circuit continued, damped only by its
natural L-C-R response.
|Figure 2: The circuit diagram of the December 1901
Poldhu transmitter in J.A. Fleming's handwriting. (Bondyopadhyay)
The Poldhu transmitter was a curious two-stage circuit, in which a
first-stage spark at some attainable lower voltage provided the energy for the second
stage in tandem (Fig. 2), to spark at a specified higher voltage. While this voltage
multiplication system was innovative in the field of wireless at the time, it carried
with it many problems, and the inefficiencies of two spark stages.
Marconi clearly realized that to achieve high power from a spark
transmitter it was necessary to charge the condenser to a very high voltage (voltages
of up to 150 kV were spoken about and may have been realized); and that a very large
discharge capacitance was needed, since the stored energy in the condenser was
understood (Energy equals 1/2 CV2). But he carried the latter requirement
to an extreme.
The power capability of the Poldhu AC generator (25 amperes at
1500 volts) in 1901 was quite insufficient to recharge the condenser every period. It
seems like several periods of the supply generator (operating at 36 Hz) were required
to bring the condenser voltage to gap break-down potential. Fleming's estimates of
the spark rate lie between wide limits. Thackeray  has estimated that the spark
rate for the primary circuit was 7.5 to 12 sparks/sec at most; and the spark rate for
the secondary circuit might have been as low as two or three sparks/sec. After that
time there was clearly a redesign to a single-stage transmitter that sparked directly
from the power transformer; and Fleming began to develop rotating dischargers in an
attempt to achieve rapid quenching of the spark.
It is perhaps ironic that the low spark rate was compromised by
Marconi himself, when in Newfoundland he put a telephone receiver to his ear to
listen for the dot transmissions from Poldhu. At the low spark rate he employed all
he would hear would be a click, not distinguishable from an atmospheric. But recall
that Marconi's early experience was with coherer-type detectors, which worked best
when the spark rate was low.
|Figure 3: Clifden, Ireland condenser under
construction. (Marconi Company)
Before leaving our discussion about Marconi's methodology, let me
comment on some of the physical arrangements for his stations. The discharge
capacitor for his Clifden and Marconi Towers, Glace Bay stations consisted of
thousands of steel plates hanging from floor to ceiling, which filled the wings of
the building, and this room was subsequently called the "condenser building" (see
Fig. 3). The power supply was a 15 kV DC generator (three 5 kV generators in series)
driven by a steam engine. Note the power source was DC. Standby batteries (6000, 2
volt, 30 AH batteries in series) at both stations may well have been the largest
battery the world has ever seen. The heart of his Clifden/Marconi Towers stations was
a whirling five foot spark discharge disk, with studs on its perimeter. Each time a
stud passed between two electrodes, a 15 kV spark jumped the gaps. The regular spark
rate was about 350 sparks/sec. The awesome size of the station and the din of the
transmitter must have been something to behold. The power consumed by these stations
was in the range of 100 to 300 kW, and the spark was a display of raw power. It is
said that the awesome din of the transmitter could be heard several kilometres
Fessenden's technology and circuit arrangements were very
different. He tried all the various methods of generating wireless signals in the
early days, by spark, by arc and by the high frequency alternator. It is likely that
he would have used the HF alternator from the outset, see for example his patent No.
706,787 filed 29 May 1901; excepting that a suitable HF alternator, generating
frequencies above about 10 kHz was not available until 1906. There is no fundamental
reason that long distance wireless communications could not have begun at VLF, except
for the practical realization of efficient antenna systems for such a low
Fessenden's work was dominated by his interest in transmitting
words without wires. By 1903 and 1904 fairly satisfactory speech had been transmitted
by the arc method, but the news of Marconi's attempts to achieve transatlantic
wireless telegraphy transmission had caught the attention of the world. Since the
development of his HF alternator was taking longer than anticipated, Fessenden set
his mind to make a more CW-like spark transmitter. This led to the development of the
synchronous rotary-spark-gap transmitter. An AC generator was used, driven by a steam
engine, which as well as providing the energy for the spark transmitter, was directly
coupled to a rotating spark gap so that sparks occurred at precise points on the
input wave, viz. at waveform maximum for best efficiency. The spark was between fixed
terminals on the stator and terminals on the rotor, which was in effect a spoked
wheel, rotating in synchronism with the AC generator.
As the speed of the wheel and the AC frequency both depend on the
speed of the generator, the number of times/sec at which the condenser voltage
reaches a peak value and the number of opportunities it has for discharging can be
made equal, and the positions of the stator terminals can be arranged so that these
conditions occur simultaneously. Another advantage was realized, since in effect a
rotary gap was a kind of a mechanically quenched spark-gap transmitter. The
oscillations in the primary circuit ceased after a few oscillations, when the
rotating gap opened. The quenched gap was more efficient and certainly less noisy
than the unquenched gap. With a synchronous spark-discharger phased to fire on both
positive and negative peaks of a 3-phase waveform, precisely at waveform peak, a 125
Hz generator could produce a spark rate of 750 times a second. These rotating gaps
produced clear almost musical signals, very distinctive and easily distinguished from
any other signal at the time. It was not true CW but it came as close as possible to
that, and the musical tone could be easily read through noise and interference from
Fessenden's Brant Rock and Machrihanish stations employed a rotary
gap 1.8 metres in diameter at the rotor. Its rotor had 50 electrodes (poles) and its
stator had four. It was driven by a 35 kVA alternator, powered by a steam engine.
The synchronous rotary gap spark discharger should not be confused
with the asynchronous rotary gap that was in more general use at the time (e.g. by
Marconi ship-borne equipment, and radio amateurs in general used asynchronous rotary
gaps). Here the speed of rotation of the wheel is entirely independent of the speed
of the generator, and while it was possible to realize several sparks during one
cycle of the generator, the sparks occur at different points on the cycle. The
conditions are not exactly repeated each time as in the case of the synchronous
spark, because the charging current from the generator is charging up the condenser
during different parts of its own cycle of variation, and hence neither the voltage
to which it is charged, nor the breakdown voltage is constant. Not only is it
possible to miss a spark altogether, but the interval between sparks is not
absolutely constant. In addition, the energy stored in the condenser and the
proportion radiated in the separate wave trains is variable. The result is that the
note heard at the receiving station is impure.
By the summer of 1906 many of the difficulties had been overcome
and the Alexanderson HF alternator developed by GE for Fessenden giving 50 kHz was
installed at Brant Rock. Various improvements were made by Fessenden and his
assistants, and by the fall of 1906 the alternator was working regularly at 75 kHz
with an output of one half a kilowatt. This was the beginning of pure CW
transmission, c.f. Alexanderson .
Continuous waves was the method of generation Fessenden had long
sought, since he wanted to transmit words without wires. He inserted a carbon
microphone in series with the lead from his alternator to the antenna, and he had an
amplitude modulated transmitter. But more on that later.
|Figure 4: The Italian Navy coherer as patented by
Marconi in September 1901 (Brit. Pat. 18 105). (Phillips)
The ability to receive wireless signals at the turn of the century
was very poor, for several reasons: 1) Initially the receiver was untuned or if tuned
the selectivity was poor; 2) there was no means to amplify the signal; and 3) a
sensitive detector had yet to be invented.
The early experiments employed a device called a coherer. The
coherer as we have noted was a device which normally exhibited a high resistance, but
when subject to a voltage above a given threshold there was a marked decrease in this
resistance. The change in resistance could be detected by means of a secondary relay
circuit, or by listening to the current change with a telephone earpierce. The
filings coherer was a bistable device. It needed an electrical voltage to effect one
transition, and a physical shock (a tapper) to return it to its initial state. The
sensitivity of the device was poor; the action of the receiver depended upon a
voltage rise and so was independent of the energy of the signal; it did not
discriminate between impulses of different character, viz. between signals and
atmospherics; the selectivity of the receiver was a function of the state of the
coherer; and it could not be used as a detector for continuous waves.
For his transatlantic experiment in 1901 Marconi had two types of
receivers, and three types of coherers. One was a tuned receiver, which he referred
to as a "syntonic receiver", that is a receiver tuned to the frequency of the
transmitter. The second earlier receiver was untuned. The three types of coherers
that he used were: one containing loose carbon filings; another designed by Marconi
containing a mixture of carbon dust and cobalt dust; and thirdly the Italian Navy
coherer (see Fig. 4) containing a globule of mercury between a carbon plug and a
moveable iron plug. This latter device, when critically adjusted or more or less by
luck, acted like a crude form of a rectifier, but its performance was poor and
unpredictable [Phillips, 1993]. Later, in 1902, he devised a form of current operated
receiver, called a magnetic detector, which greatly enhanced his receiver
sensitivity. This detector was used by Marconi until it was replaced by the vacuum
tube in 1913.
When Marconi designed the receiver he intended to use for the
first transatlantic HF experiment, he designed it so it could be tuned, and so
respond selectively to signals of different frequencies -- his famous four sevens
patent of 1900. This idea was however not his own, as was the case for many of
Marconi's "inventions", but was devised by Oliver Lodge, who in 1897 had filed four
patents. Two dealt with improvements to coherers, and two to "tuning" or "syntony"
|Figure 5: An early version of Fessenden's receiver
which employed an electrolytic rectifier (his barretter), a battery and
earphones. (John Belrose)
Fessenden was convinced that a successful detector for reception
of wireless signals must be constantly receptive, instead of requiring resetting as
was the characteristic of the coherer. Although his experiments with wireless
receivers began when he was a Professor of Electrical Engineering in the Western
University of Pennyslvania, in 1896/97; it was not until 1901/02 that he discovered
the electrolytic detector. In 1902 and 1903 he patented the first practical detector
[US Patents 706,744 and 727,331] -- which he called a barretter, a name coined from
the French word for exchanger. This name implies the exchange of AC for DC, i.e. the
device behaved like a rectifier, c.f. [Pickworth, 1994]. In Fig. 5 we sketch one of
Fessenden's early radio receivers using this detector; which was the standard of
sensitivity for many years until it was replaced by the vacuum tube some ten years
Fessenden's barretter detector was however useless for reception
of unmodulated CW. All that one would hear would be the clicks as the Morse telegraph
key was closed and opened. However, very early, some 11 years ahead of its time,
Fessenden's fertile mind had already devised a solution. He invented the methodology
(and the word) for combining two frequencies to derive their sum and difference
frequencies, viz. the heterodyne method of detecting continuous waves (US Pat. No.
706,740 dated 12 August 1902; and Nos. 1,050,441 and 1,050,728 dated 14 January,
1913). But it was not before 1912-1914, when the triode's versatility to be an
oscillator, or RF source, was established, that the heterodyne receiver became a
practical method for detecting CW. Today, heterodyning is fundamental to the
technology of radio communications.
Fleming in 1904 invented the valve diode (known as a Fleming
valve). The patent which covered its use as a detector of Hertzian waves became the
property of the Marconi Company, and eventually, but not until after WWI, Fleming
valves were put into operation in Marconi stations.
Meanwhile de Forest, who was following the footsteps of Fessenden,
experimenting with the electric arc as a CW wireless transmitter for telephony needed
a good detector. The electrolytic detector that he had been using was judged by The
Courts in 1906 to be an infringement on Fessenden's patent. As a result he had to
change all of his stations to use the silicon detector, which had been patented in
1906 by H.H. Dunwoody, an officer in his company. Because of this incident, de Forest
resigned from the company in November 1906. De Forest started looking for a better
valve detector. He made some Fleming valves, and, in a moment of inspiration, he
added a third element, a control element shaped like a grid-iron, called a grid. De
Forest patented his audion, the first three-element valve in 1907. Although the
audion was more sensitive as a detector than the Fleming valve he was prevented from
using it for commercial purposes, by a lawsuit launched by the Marconi Company
(claiming infringement in spite of the fact that it was a different valve). De Forest
did not understand how the valve operated, and it remained for Langmuir, Armstrong,
and van der Pol to discover its full possibilities. The time interval between
Fessenden's heterodyne receiver (1902) and Armstrong's "feedback" receiver or
regenerative receiver (1913) is the 11 years mentioned above. Armstrong's
superheterodyne receiver was not invented until 1918.
4. The First Transatlantic Experiment
On 12 December 1901 signals from a high power spark transmitter
located at Poldhu were reported to have been received by Marconi and his assistant
George Kemp, at a receiving station on Signal Hill, near St. John's, Newfoundland.
The signals had traveled a distance of 3500 kilometres. Even at the time of the
experiment there were those who said, indeed there are some who still say, that he
misled himself and the world into believing that atmospheric noise crackling was in
fact the Morse code letter 'S'.
A little later, in February 1902, when Marconi returned to England
on the SS Philadelphia, using a tuned ship-borne antenna, he received signals using
his filings coherer from the same sender up to distances of 1120 km by day and 2500
km by night. Even these distances are rather remarkable considering the receiving
apparatus he used.
We discuss here in detail that first transatlantic experiment.
The Poldhu Station
Marconi's ambition at the turn of the century to demonstrate
long-distance wireless communication, and develop a profitable long-distance wireless
telegraph service, led to his pragmatic proposal in 1900 to send a wireless signal
across the Atlantic. He conceived a plan to erect two super-stations, one on each
side of the Atlantic, for two-way wireless communications, to bridge the two
continents together in direct opposition to the cable company (Anglo-American
Telegraph Company). For the eastern terminal, he leased land overlooking Poldhu cove
in southwestern Cornwall, England. For the western terminal the sand dunes on the
northern end of Cape Cod, MA at South Wellfleet, was chosen.
The aerial systems comprised 20 masts, each 61 metres high,
arranged in a circle 61 m in diameter. The ring of masts supported a conical aerial
system of 400 wires, each insulated at the top and connected at the bottom, thus
forming an inverted cone. Vyvyan , the Marconi engineer who worked on the 1901
experiment, when shown the plan, did not think the design sound. Each mast was stayed
to the next one, and only to ground in a radial direction, to and away from the
centre of the mast system. He was overruled, construction went ahead, and both aerial
systems were completed in early 1901.
However, before testing could begin catastrophe struck, the Poldhu
aerial collapsed in a storm on 17 September, and the South Wellfleet aerial suffered
the same fate on 26 November, 1901.
At Poldhu Marconi quickly erected two masts and put up an aerial
of 54 wires, spaced 1 metre apart, and suspended from a triadic stay stretched
between these masts at a height of 45.7 m. The aerial wires were arranged fan shaped,
presumably insulated at the top, as was his conical wire aerial, and connected
together at the lower end, see Fig. 1. This photograph has been published and
republished, and clearly one can see only 12 wires -- but the view generally held is
that the aerial system as described above by Vyvyan [1933) is right, that is there
were 54 wires, and the photograph has been retouched.
The antenna was driven by the curious two stage spark transmitter,
previously discussed. There were many problems in getting it to work at the high
power levels desired [see Thackeray, 1992]. Our principal concern here is the
frequency generated by the Poldhu station. The oscillation frequency is determined by
the natural resonant response of the antenna system, which includes the inductance of
the secondary of the antenna transformer T2, since in effect the antenna
system is a base-loaded monopole (see Fig. 2).
The primary of this transformer consisted of 2 7/20 wires in
parallel, the secondary consisted of 7 or 9 wires of 7/20 wire in series. Fleming's
sketch indicates 9 wires; Entwisle  said there were 7 wires. The inductance
values for this transformer have long been debated, since the original transformer is
lost, there are no drawings, and reports about them differ [Thackeray, 1992]. G.
Garratt made a copy of Ls (the secondary of this transformer) and measured
its inductance to be 6 x 10-6 H [see Ratcliffe 1974].
While the inductance Ls changes the resonant frequency,
the exact value does not change the conclusion reached in our study. For
Ls equal to 6 x 10-6 H, we have modelled Marconi's Poldhu
antenna, assuming the fan comprised 12 wires. According to the antenna analysis code
MININEC, the resonant frequency of the antenna system was 850 kHz.
A number of scientists and engineers interested in the actual
frequency or frequencies radiated by this first high power transmitter at Poldhu have
discussed the possibility that the aerial transformer was overcoupled, resulting in a
double-humped frequency/amplitude response. We do know that Fleming tuned the primary
oscillatory circuit by varying the discharge capacitor C2 to maximize the
aerial current. Since our best estimate for the component values (C2 =
0.037 muF and Lp = 8 x 10-7 H) would result in a resonant
frequency of 925 kHz, it seems logical to conclude that the overall system response
would result in a single peak centred on the resonant frequency of the aerial system,
viz. about 850 kHz.
Historians have also speculated that the transmitter might also
have radiated a high-frequency signal as well, since an HF signal would have been
more suitable for transatlantic communications (to be discussed), see for example
Ratcliffe . If Marconi had used a thin wire transmitting antenna at Poldhu,
this antenna would indeed have radiated efficiently at odd harmonics of the
fundamental resonant frequency. But for our model the antenna is inductive for all
frequencies greater then the fundamental resonant frequency response of the antenna
system. One must conclude therefore that the Poldhu spark-transmitter system radiated
efficiently only on the fundamental oscillation frequency of the tuned antenna system
-- about 850 kHz.
Marconi himself has been evasive concerning the frequency of his
Poldhu transmitter. Fleming in a lecture he gave in 1903 said that the wavelength was
a 1000 feet or more, say, one-fifth to one-quarter of a mile (820 kHz is the
generally quoted frequency). Marconi remained silent on this wavelength, but in 1908
in a lecture to the Royal Institution he quotes the wavelength as 1200 feet, see
Reception on Signal Hill
For his transatlantic experiment, Marconi decided to set up
receiving equipment in Newfoundland. In December 1901 he set sail for St. John's,
with a small stock of kites and balloons to keep a single wire aloft in stormy
A site was chosen on Signal Hill, and apparatus was set up in an
abandoned military hospital. A cable was sent to Poldhu, requesting that the Morse
letter " S " be transmitted continuously from 3:00 to 7:00 PM local time.
On 12th December, 1901, under strong wind conditions, a kite was
launched with a 155 m long wire. The wind carried it away. A second kite was launched
with a 152.4 m wire attached. The kite bobbed and weaved in the sky, making it
difficult for Marconi to adjust his new syntonic receiver which employed the Italian
Navy coherer. "Difficult" I will accept, but how he determined the frequency of
tuning for his receiver is a mystery to me. Whatever, because of this difficulty,
Marconi decided to use his older untuned receiver. History has assumed that he
substituted the metal filings coherer previously used with this receiver for the
newly acquired Italian Navy coherer, but Marconi never really said he did [see
Phillips, 1993]. He referred only to the use of three types of coherers.
Despite the crude equipment employed, and in our view the
impossibility of hearing the signal, Marconi and his assistant George Kemp convinced
themselves that they could hear on occasion the rhythm of three clicks more or less
buried in the static, and clicks they would be if heard at all, because of the low
spark rate. Marconi wrote in his laboratory notebook: Sigs at 12:30, 1:10 and 2:20
(local time). This notebook is in the Marconi Company archives and is the only proof
today that the signal was received.
Today we know that signals (depending on frequency used) can
indeed travel across the Atlantic, and far beyond. But in 1901, anyone who believed
that they could, and did, believed so as an act of faith based on the integrity of
one man -- Marconi.
If 850 kHz was indeed the frequency used, the tests took place at
the worst time of day, because the entire path would have been daylight, and the
daytime skywave would be heavily attenuated, even though it was a winter day, in
sunspot minimum period, and there were no magnetic storms at the time, or for ten
days before. The day-time absorption of an ionospherically-reflected signal is a
maximum in the LF/MF band. Ratcliffe  has deduced that, from a knowledge only
of propagation conditions, reception on Signal Hill is consistent with the observed
limiting ranges of reception on the ship only if the untuned landbased receiver was
10-100 times more sensitive than the tuned receiver on the ship.
It is therefore difficult to believe that signals could have been
heard on Signal Hill, since the receiving equipment after all consisted of a
long-wire antenna, coupled to an untuned receiver which had no means of amplification
whatsoever, and the type of detector used was less sensitive and its performance
unpredictable compared with Fessenden's barretter detector, or the galena crystal
detector which evolved a few years later.
|Figure 6: Curve showing the variaton of the
intensity of transatlantic signals for the month of January, 1906. Unity
corresponds to a just audible message. Such a curve is certainly one of the first
reocrdings of LF propagation data. (Fessenden)
5. The First Radio Propagation Experiments
There is no evidence that Marconi made any serious attempt to
systematically investigate the charactericistics of the HF, MF and LF portions of the
radio frequency spectrum when he began the downward frequency trend, in his struggle
to achieve transatlantic wireless communications. He did not do this until 20 years
later, in the early 1920's, when attracted to the HF band by amateur radio operators.
The radio amateurs had been banished to the then-believed useless frequencies higher
than 1500 kHz.
The first record showing qualitatively the variation of the
intensity of transatlantic messages transmitted between Brant Rock, MA and
Machrihanish, Scotland, at night, during the month of January 1906 is reproduced in
Fig. 6 [Fessenden, 1908]. Nothing at all was received that month during daytime.
It was found (measurements made during 1906) that absorption at a
given instant was a function of direction as well as distance, since on a given night
the signals received by stations in one direction would be greatly weakened, while
there would be less weakening of the signals received by stations lying in another
direction; and a few hours or minutes later the reverse would be the case. It was
also found that variations of absorption on transatlantic signals appeared to have a
quite definite relation with variations of the geomagnetic field, i.e., the greater
the absorption the greater the magnetic variation [Fessenden, 1908].
Experiments were made between Brant Rock and the West Indies, a
distance of 2735 km, during the spring and summer of 1907. Frequencies in the band 50
kHz to 200 kHz were used. It was found that the absorption at 200 kHz was very much
greater than at 80 kHz, and that messages could be successfully received over this
path in daytime at the latter frequency. Antenna radiation efficiency was an
important factor for frequencies less than 80 kHz. No messages were received in
daytime with the higher frequency.
The fact that these experiments were made during summer, that the
receiving station was in the Tropics (high noise levels), and the fact that the
distance, 2735 km was practically the same as between Ireland and Newfoundland was
reported by Fessenden . After publication of the above results, Marconi, in
early October, 1907 abandoned his previously used frequencies, and immediately
succeeded in operating between Glace Bay and Clifden, a distance of more than 3000
km, the frequency being about 70 kHz. The same messages were received at Brant Rock,
MA, a distance of nearly 4825 km. A little later Marconi moved to an even lower
frequency, 45 kHz.
6. Verifiable Transatlantic Radio
The first East-West transatlantic radio transmission was made
during October 1902 from Poldhu, Cornwall to the Italian cruiser Carlos Alberto
anchored in the harbour of Sydney, NS with Marconi aboard. The frequency employed was
about 272 kHz. This successful transmission was considered an experimental
prerequisite to the start-up of the permanent land based wireless Marconi station
under construction at Glace Bay, NS.
The first West-East transatlantic radio transmission was recorded
on 5 December 1902 between Glace Bay and Poldhu. The frequency was about 182 kHz.
The first Canada/UK transatlantic radio message (as opposed to
hearing the signal) was sent from Glace Bay to Poldhu on 15 December 1902. It was a
press message from a London Times correspondent at Glace Bay to his home office.
The first USA/UK transatlantic radio message received at Poldhu
from the Marconi station at South Wellfleet, MA was from President Roosevelt to King
Edward VII, on 18 January, 1903.
History has recorded that the above messages were successfully
transmitted, but how well these messages were received is a matter of conjecture. In
1902-c.1912, both the Clifden and Glace Bay stations were using "disc discharger"
transmitters, and a form of current operated receiver (Marconi's magnetic detector).
It is clear that Marconi was still struggling in 1908 to achieve reliable
transatlantic radio communications. It is interesting to read a letter written on 19
March, 1909 to Hon. Chauncey M. Depew, US Senate, Washington, DC, signed by five
members of The Junior Wireless Club (now The Radio Club of America). The thrust of
the letter was to comment on a proposed bill before the Senate, that would in effect
restrict the use of the air waves by radio amateurs, because of presumed malicious
interference caused by radio amateurs. I quote from a part of that letter, which can
be found in the Seventy-Fifth Anniversary Diamond Jubilee Year Book of The Radio Club
of America, 1984:
"At the Narragansett Bay there were certain Naval tests made
about two years ago, and the various so-called Wireless Companies wanted to get the
first news to the newspapers of these tests, so as to boom their companies' stocks,
and to say the news was received first through their company, and when some of them
found they were unable to cut out interference between themselves, in order to
prevent other Wireless Companies from getting the news first they sent a lot of
fake messages of confused dashes.
"Only a few of the so-called Wireless Companies have efficient
methods of cutting out interference, and these are the companies that are now
crying for the most protection.
"You probably have heard of the tests made last year between
Glace Bay, NS and Clifden, Ireland, when the National (Electric) Signaling Company
(Fessenden's Brant Rock station) picked up the messages, which Marconi, on the
test, was unable to deliver between his own stations, from both Glace Bay and
Clifden, Ireland, in spite of the fact that the Marconi Company kept up a constant
interference of dash, dash dash, from their Cape Cod Station for 48 hours without
interruption, but the National (Electric) Signaling Company paid no attention to
such interference and picked up all the messages, which Marconi was unable to
exchange between their own stations, and all these messages were handed over to
Lord Northcutt at the Hotel St. Regis."
Marconi himself, in his 1909 Nobel Prize address said: "What often
happens in pioneer work repeated itself in the case of radiotelegraphy. The
anticipated obstacles or difficulties were purely imaginary or else easily
surmountable, but in their place unexpected barriers presented themselves, and recent
work has been directed to the solutions of problems that were neither expected or
anticipated when long distances were first attempted". Certainly after Marconi's
first transatlantic radio experiment in 1901, he found that the realization of
reliable transatlantic radio communications was more distant (for him) than he
realized at the time.
The first two-way transatlantic radio telegraphy transmission took
place on 10 January 1906, between Fessenden's stations at Brant Rock, MA and
Machrihanish Scotland. Repeatedly regular exchange of messages across the Atlantic
Ocean took place on most days during winter, spring and into early summer. The
frequencies used were in the 80-100 kHz band. The reliability and the quality of
signal reception (signal-to-noise ratio) for the Fessenden system must have been very
much better than anything Marconi could achieve at this point in time. Fessenden was
using his synchronous rotary-spark transmitters at both ends, and tuned receivers
with his barretter detector. The signals were superior to other signals used at the
time, which by comparison were rough and ragged. His antenna system was an umbrella
top-loaded radiator 128 metres high. The Marconi antennas were multi-wire conical
structures, or wire antennas with extensive top loading, 61 metres high. Since the
radiation efficiency of electrically short antennas varies (approximately) as the
height of the antenna red, Fessenden's antenna systems were probably four times more
efficient than Marconi's.
At the turn of the century Fessenden was using a spark
transmitter, employing a Wehnelt interrupter operating a Ruhmkorff induction coil. In
1899 he noted, when the key was held down for a long dash, that the peculiar wailing
sound of the Wehnelt interrupter could be clearly heard in the receiving telephone.
He must have had a detector of some sort that was working for him, even at this early
stage in the development of wireless. This suggested to him that by using a spark
rate well above voice band (10,000 sparks/sec), wireless telephony could be achieved;
and this he did transmitting speech over a distance of 1.5 km on 23 December 1900,
between 15 metre masts on Cob Island, MD [Belrose, 1994a; 1994b].
In autumn of 1906 Fessenden had his HF alternator working
adequately on frequencies up to about 100 kHz. About midnight in November, 1906 Mr.
Stein at Fessenden's Brant Rock station was telling the operator at a nearby test
station at Plymouth, MA how to run the HF alternator. It was usual for these two
operators to use speech over this short distance. However his voice was heard by Mr.
Armor at Machrihanish, Scotland with such clarity that there was no doubt about the
speaker, and the station log books confirmed the report.
Fessenden's equipment was working exceptionally well in the early
hours of that morning, and (remarkable for that time) the echo of the telegraphy
signals from the Scotland station could clearly be heard one fifth of a second later,
having travelled the long way around the earth.
The Machrihanish tower crashed to the ground on 5 December, 1906
during a severe winter storm. The station was never rebuilt, and so Fessendeil's
transatlantic experiments came to an abrupt end.
Fessenden's greatest success took place on Christmas Eve 1906,
when he and his colleagues presented the world's first wireless broadcast. The
transmission included a speech by Fessenden and selected music for Christmas.
Fessenden played Handel's Largo on the violin. That first broadcast, from his
transmitter at Brant Rock, MA was heard by radio operators on board US Navy and
United Fruit Company ships equipped with Fessenden's wireless receivers at various
distances over the South and North Atlantic, and in the West Indies. The wireless
broadcast was repeated on New Year's Eve. The transmitter was an HF alternator, in
which one terminal was connected to ground, the other terminal to the tuned antenna,
and a carbon microphone was inserted in the antenna lead.
Recall that Fleming, in the first edition of his book on
Electromagnetic Waves published in 1906, stated that an abrupt impulse was a
necessary condition for wireless transmission, and that high frequency currents, even
of sufficient frequency could not produce radiation. The highest frequency of HF
alternators prior to the summer of 1906 was about 10 kHz. This belief, and an earlier
belief that the terminals of an antenna had to be bridged by a spark, show how wrong
some of the early "experts" were.
Continuing in the same vein, Fessenden in his 1908 paper restated
his long held view: "The coherer is well adapted for working with damped waves, but
the coherer-damped wave method can never be developed into a practical telegraph
system. It is a question whether the invention of the coherer has not been on the
whole a misfortune as tending to lead development of the art astray into
impracticable and futile lines, and thereby retarding the development of a really
7. Concluding Remarks
There are those that say that Marconi's greatest triumph (the
mother of all experiments) was when he succeeded in 1901 in passing signals across
the Atlantic. There are those that say that he misled himself and the world into
believing that atmospheric noise crackling was in fact the Morse code letter 'S'.
Whether Marconi heard the three faint dots or not is really unimportant. His claim
"sparked" a controversy among contemporary scientists and engineers about the
experiment that continues today.
Certainly engineers and scientists of the present day are
unanimous in admiring the bold and imaginative way in which Marconi attempted to take
one spectacular step forward, to extend the range of wireless communications from one
or two hundred kilometres to the 3500 kilometre distance across the Atlantic
The world has acclaimed Marconi as the "father of wireless",
although some say that Alexander Popov and Oliver Lodge were first in the field.
History has accredited Marconi with the invention of an early form of radio
Fessenden's continuous waves, a new type of detector, and, his
invention of the method as well as the coining of the word heterodyne, did not by any
means constitute a satisfactory wireless telegraphy or wireless telephony system,
judged by today's standards. They were, however, the first real departure from
Marconi's damped-wave-coherer system for telegraphy which other experimenters were
merely imitating or modifying. They were the first pioneering steps toward radio
communications and radio broadcasting.
Today, heterodyning is fundamental to the technology of radio
communications. Some historians consider that Fessenden's heterodyne principle is his
greatest contribution to radio science. Edwin Howard Armstrong's super-heterodyne
receiver is based on the heterodyne principle. Except for method improvement
Armstrong's superheterodyne receiver remains the standard radio receiving method
Fessenden, a genius, and a mathematician was the inventor of radio
as we know it today.
Alexanderson, E.F.W. , "Transatlantic Radio Communication",
Trans. AIEE, pp. 1077-1093.
Austin, B.A. , "Oliver Lodge - The Forgotton Man of Radio?",
The Radioscientist & Bulletin, Vol. 5, No. 4. pp. 12-16, URSI, Gent, Belgium.
Belrose, J.S. , "Fessenden and the Early History of Radio
Science', Radioscientist & Bulletin, Vol. 5, No. 3, URSI, Gent, Belgium, pp.
Belrose, J.S. , "Sounds of a Spark Transmitter", multimedia
article published on URSI Radioscientist On-Line on the World Wide Web. Address is:
Bondyopadhyay, P.B. , "Investigations on the Correct
Wavelength of Transmission of Marconi's December 1901 Transatlantic Wireless Signal",
IEEE Antennas and Propagation Society, International Symposium Digest, Vol. 1, pp. 72
Entwisle , "Year Book of Wireless Telegraphy", Wireless
Fessenden, R.A. [19071, The Electrician (London), July 26.
Fessenden, R.A. , "Wireless Telephony", A paper presented at
the 25th annual convention of the American Institute of Electrical Engineers,
Atlantic City, NJ, June 20, 1908.
Phillips, V.J. , "The 'Italian Navy Coherer' affair
turn-of-the-century scandal", IEE Proceedings A, Vol. 140, pp. 175-185.
Pickworth, G. , "Detection before the diode", Electronics
World + Wireless World, December 1994, pp. 1003-1006; and January 1995, pp.
Ratcliffe, J.A. , "Scientists' reactions to Marconi's
transatlantic radio experiment', Proc. IEE, 121, pp. 1033-1038.
Thackeray, D. , "The First High-Power Transmitter at
Poldhu', The AWA Review, Vol. 7, pp 29-45.
Vyvyan, R.N. , "Marconi and his Wireless", EP Publishing,
1974. First published as "Wireless over 30 Years", by Routledge and Keegan.
References Not Cited
"Guglielmo Marconi", compiled by Pam Reynolds published by the
Marconi Company, Chelmsford, 1984.
"Marconi Towers - Proposals for the Preservation and Development
of the Marconi Historic Site" A Study for Marconi Museums Association, PO Box 156,
Marion Bridge, NS.
"Register of the George H. Clark Radioana Collection c.
1880-1950", by Robert S. Harding, Archives Center, National Museum of American
History, Washington, DC, 1990.