Arc converter
Encyclopedia
The arc converter, sometimes called the arc transmitter or Poulsen arc after its inventor Danish engineer Valdemar Poulsen
, is a device that used an electric arc
to convert direct current
electricity into radio frequency
alternating current
. It was used in radio transmitter
s for a short period around 1920 before it was replaced by vacuum tube
s, and was one of the first technologies that was used to transmit sound (amplitude modulation
) by radio. It is now on the list of IEEE Milestones as a historic achievement in electrical engineering
.
discovered how to make a resonant circuit using a carbon arc lamp. Duddell's "musical arc" operated at audio frequencies, and Duddell himself concluded that it was impossible to make the arc oscillate at radio frequencies.
Valdemar Poulsen
, who had demonstrated the 'Telegraphone' (the world's first magnetic recording device) at the Paris Exhibition of 1900, turned his inventive genius to the problem and succeeded in raising the efficiency and frequency
to the desired level; Poulsen's arc could generate frequencies of up to 200 kilohertz
and was patented in 1903.
After a few years of development the arc technology
was transferred to Germany
and Great Britain
in 1906 by Poulsen, his collaborator Peder Oluf Pedersen
and their financial backers. In 1909 the American patents as well as a few arc converters were bought by Cyril F. Elwell. The subsequent development in Europe and the United States
was rather different, since in Europe
there were severe difficulties for many years implementing the Poulsen technology, whereas in the United States an extended commercial radiotelegraph
system was soon established with the Federal Telegraph Company
. Later the US Navy also adopted the Poulsen system. Only the arc converter with passive frequency conversion was suitable for portable and maritime use. This made it the most important mobile radio
system for about a decade until it was superseded by vacuum tube
systems.
converter, the arc converter produces undamped or continuous wave
s (CW). This was an important feature as the use of damped wave
s resulted in lower transmitter efficiency and communications effectiveness, while covering the RF spectrum with interference. This more refined method for generating continuous-wave radio signals was initially developed by Danish inventor Valdemar Poulsen
.
The Poulsen arc converter can be likened to a continuous-duty-rated electric arc welder
with a tuned circuit connected across the arc. The negative resistance
characteristics of an electric arc
permits the creation of a relaxation oscillator
that converts direct current
to radio frequency
energy. The arc converter consisted of a water-cooled bronze
chamber in which the arc burned in hydrogen
gas between a carbon
cathode
and a water-cooled copper
anode
. Above and below this chamber there were two series field coil
s surrounding and energizing the two poles of the magnetic circuit. These poles projected into the chamber, one on each side of the arc to provide a magnetic field
. This field helps to stabilize the arc and improve overall conversion efficiency. In today's world one can still find oscillators based on negative resistance devices; the tunnel diode
is one of them.
Since the arc took some time to strike and operate in a stable fashion, normal on-off keying
could not be used. Instead, a form of frequency shift keying was employed. The arc was left operating continuously and a portion of the tuned circuit was shorted out when the key closed. Therefore, the "mark" (key closed) was sent at one frequency; the "space" (key open) at another frequency. If these frequencies were far enough apart, and the receiving station's receiver
had adequate selectivity
, the receiving station would hear standard CW when tuned to the "mark" frequency. This emission of signals at two differing frequencies was eliminated by the development of uniwave keying by Lt. W. A. Eaton, USN. wherein the generated energy was dissipated in to a noninductive resistive
absorbing circuit during open key periods.
It was most successful when made to operate in the frequency range of a few kilohertz to a few tens of kilohertz. The passive frequency multiplier
was relied upon to bring the output frequency up to practical transmission frequencies.The frequency multiplier and antenna tuning
had to be selective enough to suppress the high harmonic
output of the arc converter.
Valdemar Poulsen
Valdemar Poulsen was a Danish engineer who developed a magnetic wire recorder in 1899.-Biography:He was born on 23 November 1869 in Copenhagen...
, is a device that used an electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
to convert direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
electricity into radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
. It was used in radio transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
s for a short period around 1920 before it was replaced by vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s, and was one of the first technologies that was used to transmit sound (amplitude modulation
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
) by radio. It is now on the list of IEEE Milestones as a historic achievement in electrical engineering
Electrical engineering
Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...
.
History
The English engineer William DuddellWilliam Duddell
William Du Bois Duddell was a British electro-physicist and electrical engineer. He was privately educated in the UK and France and rose quickly through the prestigious City & Guilds Schools via scholarships...
discovered how to make a resonant circuit using a carbon arc lamp. Duddell's "musical arc" operated at audio frequencies, and Duddell himself concluded that it was impossible to make the arc oscillate at radio frequencies.
Valdemar Poulsen
Valdemar Poulsen
Valdemar Poulsen was a Danish engineer who developed a magnetic wire recorder in 1899.-Biography:He was born on 23 November 1869 in Copenhagen...
, who had demonstrated the 'Telegraphone' (the world's first magnetic recording device) at the Paris Exhibition of 1900, turned his inventive genius to the problem and succeeded in raising the efficiency and frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
to the desired level; Poulsen's arc could generate frequencies of up to 200 kilohertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
and was patented in 1903.
After a few years of development the arc technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...
was transferred to Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
in 1906 by Poulsen, his collaborator Peder Oluf Pedersen
Peder Oluf Pedersen
Peder Oluf Pedersen was a Danish engineer and physicist. He is notable for his work on electrotechnology and his cooperation with Valdemar Poulsen on the developmental work on the telegraphone and the Poulsen Arc Transmitter....
and their financial backers. In 1909 the American patents as well as a few arc converters were bought by Cyril F. Elwell. The subsequent development in Europe and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
was rather different, since in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
there were severe difficulties for many years implementing the Poulsen technology, whereas in the United States an extended commercial radiotelegraph
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...
system was soon established with the Federal Telegraph Company
Federal Telegraph Company
The Federal Telegraph Company was a United States communications company that played a pivotal role in the 20th century in the development of radio communications. Founded in Palo Alto, California in 1909, it would eventually merge in August 1927 with the Mackay Companies...
. Later the US Navy also adopted the Poulsen system. Only the arc converter with passive frequency conversion was suitable for portable and maritime use. This made it the most important mobile radio
Mobile Radio
This article is about professional equipment. For mobile radios used in amateur radio, see amateur radio mobile operation. Mobile radio or mobiles refer to wireless communications systems and devices which are based on radio frequencies, and where the path of communications is movable on either...
system for about a decade until it was superseded by vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
systems.
Description
Unlike the spark-gap transmitterSpark-gap transmitter
A spark-gap transmitter is a device for generating radio frequency electromagnetic waves using a spark gap.These devices served as the transmitters for most wireless telegraphy systems for the first three decades of radio and the first demonstrations of practical radio were carried out using them...
converter, the arc converter produces undamped or continuous wave
Continuous wave
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
s (CW). This was an important feature as the use of damped wave
Damped wave
A damped wave is a wave whose amplitude of oscillation decreases with time, eventually going to zero. This term also refers to an early method of radio transmission produced by spark gap transmitters, which consisted of a series of damped electromagnetic waves...
s resulted in lower transmitter efficiency and communications effectiveness, while covering the RF spectrum with interference. This more refined method for generating continuous-wave radio signals was initially developed by Danish inventor Valdemar Poulsen
Valdemar Poulsen
Valdemar Poulsen was a Danish engineer who developed a magnetic wire recorder in 1899.-Biography:He was born on 23 November 1869 in Copenhagen...
.
The Poulsen arc converter can be likened to a continuous-duty-rated electric arc welder
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...
with a tuned circuit connected across the arc. The negative resistance
Negative resistance
Negative resistance is a property of some electric circuits where an increase in the current entering a port results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions. Negative resistors are...
characteristics of an electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
permits the creation of a relaxation oscillator
Relaxation oscillator
A relaxation oscillator is an oscillator based upon the behavior of a physical system's return to equilibrium after being disturbed. That is, a dynamical system within the oscillator continuously dissipates its internal energy...
that converts direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
to radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
energy. The arc converter consisted of a water-cooled bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
chamber in which the arc burned in hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas between a carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
and a water-cooled copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
. Above and below this chamber there were two series field coil
Field coil
A field coil is a component of an electro-magnetic machine, typically a rotating electrical machine such as a motor or generator. A current-carrying coil is used to generate a magnetic field....
s surrounding and energizing the two poles of the magnetic circuit. These poles projected into the chamber, one on each side of the arc to provide a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
. This field helps to stabilize the arc and improve overall conversion efficiency. In today's world one can still find oscillators based on negative resistance devices; the tunnel diode
Tunnel diode
A tunnel diode or Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave frequency region, by using quantum mechanical effects....
is one of them.
Since the arc took some time to strike and operate in a stable fashion, normal on-off keying
On-off keying
On-off keying the simplest form of amplitude-shift keying modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a...
could not be used. Instead, a form of frequency shift keying was employed. The arc was left operating continuously and a portion of the tuned circuit was shorted out when the key closed. Therefore, the "mark" (key closed) was sent at one frequency; the "space" (key open) at another frequency. If these frequencies were far enough apart, and the receiving station's receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
had adequate selectivity
Selectivity
Selectivity may refer to:* Selectivity , in radio transmission* Binding selectivity, in pharmacology* Functional selectivity, in pharmacology* Socioemotional selectivity theory, in social psychology...
, the receiving station would hear standard CW when tuned to the "mark" frequency. This emission of signals at two differing frequencies was eliminated by the development of uniwave keying by Lt. W. A. Eaton, USN. wherein the generated energy was dissipated in to a noninductive resistive
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
absorbing circuit during open key periods.
It was most successful when made to operate in the frequency range of a few kilohertz to a few tens of kilohertz. The passive frequency multiplier
Frequency multiplier
In electronics, a frequency multiplier is an electronic circuit that generates an output signal whose output frequency is a harmonic of its input frequency. Frequency multipliers consist of a nonlinear circuit that distorts the input signal and consequently generates harmonics of the input signal...
was relied upon to bring the output frequency up to practical transmission frequencies.The frequency multiplier and antenna tuning
Antenna tuner
An antenna tuner, transmatch or antenna tuning unit is a device connected between a radio transmitter or receiver and its antenna to improve the efficiency of the power transfer between them by matching the impedance of the equipment to the antenna...
had to be selective enough to suppress the high harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
output of the arc converter.