alternator An electrical machine, usually rotary, for producing alternating current.  See also generator.

amplitude modulation (AM) A form of carrier wave modulation in which the amplitude of the carrier wave is varied in proportion to the amplitude of the modulating wave.  See also modulation.

anode A positively charged electrode that attracts free electrons or emits positive ions.  See also cathode.

arc An intense luminous discharge formed by the passage of an electric current across a space between two electrodes.  See also streamer.

attenuation The decrease in magnitude of current, voltage, or power of a signal in transmission between two points. May be expressed in decibels.

ballast A device for starting and regulating fluorescent and high intensity discharge lamps.

ball lightning An electrical discharge which takes the form of a luminous sphere. In nature, the phenomenon is associated with thunderstorm activity. It can also be produced by high voltage multiple-resonator Tesla oscillators .

bandwidth A measure of the information carrying capacity, or size of a communication channel. For an analog circuit, the bandwidth is the difference between the highest and lowest frequencies that a medium can transmit and is expressed in hertz (Hz). *

baseband The frequency band occupied by information-bearing signals before combining with a carrier in the modulation process. *

Beat Frequency Oscillator (BFO) Any oscillator whose output is intended to be mixed with another signal to produce a sum or difference beat frequency. Used particularly in reception of CW transmissions.

capacitor/condenser An electrical device that stores energy, consisting of two parallel conductors, usually metallic foil, insulated from each other by a dielectric.

cathode A negatively charged electrode that emits free electrons or negative ions.  See also anode.

coherer A detector that depends upon a phenomenon which can occur when there is a loose or imperfect electrical connection between two or more electrical conductors such as two oxidized copper rods lying one upon the other. One form often used by Tesla is the metal filing coherer which typically consists of a short glass tube with two metal plugs fitted into its ends. The space between the plugs is partially filled with course chips of an easily oxidized metal such as nickel.

conductor Any medium capable of carrying an electrical current.

continuous wave A sustained sinusoidal oscillation or oscillatory wave in which additional energy is added during each cycle.  Also known as an undamped wave.  A continuous wave can be modulated with audio, video or data.  When the wave is unmodulated the signal is highly monochromatic.  While the term is most commonly associated with the operation of non-spark type wireless transmitters, Tesla said he was able to produce "a perfectly continuous wave" with his more advanced disruptive discharge machines.  See also damped wave.

core The center part of an inductor or transformer around which wire is wound.  Cores are typically composed of laminated steel, ferrite material, or a hollow dielectric tube, i.e., an air core.

coulomb A unit of electric charge defined as the amount of charge that crosses a surface in 1 second when a current of 1 absolute ampere is flowing across the surface. See international coulomb.

damped wave A "ringing" sinusoidal oscillation or oscillatory wave consisting of an initial pulse or peak followed by additional peaks of diminishing amplitude. The term is commonly associated with the operation of spark-type wireless transmitters.  See also continuous wave.

dB See decibel.

dBc Decibels referenced to the carrier signal.

dBi Decibels referenced to an isotropic radiator. (dBLi indicating linear isotropic radiator is sometimes used).

dBm Decibels relative to 1 mW. dBm is calculated by using the ratio of some power (expressed in mW) to 1 mW. For example, 1 mW is 0 dBm and 10 mW is +10 dBm.

dBsm Decibel referenced to one square meter.

dBv / dBµv Decibels referenced to one volt or microvolt, i.e. 0 dBv is 1 volt or 120 dBµv.

dBW / dBµW Decibels referenced to 1 watt or one microwatt, i.e. 0 dBW is 1 watt or 30 dBm or 60 dBµW.

decibel (dB) A dimensionless unit for expressing the ratio of two values of power, current, or voltage. The number of decibels being equal to: dB = 10 log P2 / P1 = 20 log V2 / V1 = 20 log I2 / I1.  Normally, used for expressing transmission gains, losses, levels, and similar quantities.

demodulation The process of recovering a baseband signal from a modulated carrier. See also modulation.

detector Device or circuit for detecting the presence of propagating electrical energy of distant origin.

dielectric An insulating medium or one in which an electric field may be easily maintained.

direct current (DC) An electric current that flows in one direction only.

disruptive discharge coil A Tesla oscillator which incorporates some form of spark gap switching device to discharge the primary capacitor(s) through the primary inductor.

downconverter A device which provides frequency conversion to a lower frequency.

dyne The unit of force equal to the force which accelerates a mass of 1 gram at a rate of 1 cm/sec-2.

earth resonance A theory which states that the earth itself constitutes a massive LC circuit which can be resonated with a sufficiently powerful and properly tuned electrical oscillator. An ability to electrically resonate the earth was the underpinning of Tesla's proposed "World System."

Effective Radiated Power (ERP) The product of the transmitter power in watts and the relative gain of the antenna as compared with a standard halfwave dipole. For example, a transmitter producing 10 watts of power connected to an antenna with a gain factor of 9, has an effective radiated power of 90 watts.

Egg of Columbus A novel demonstration apparatus used to explain the principal of the rotating magnetic field and the induction motor. It was part of the momentous exhibit at the 1893 Chicago Columbian Exposition at which Tesla and George Westinghouse first introduced the American public to the alternating current electrical power system.

elevated capacity See terminal capacity.

electromagnetic interference (EMI) Any induced, radiated, or conducted electrical emission, disturbance, or transient that causes undesirable responses, degradation in performance, or malfunctions of any electrical or electronic equipment, device, or system. Also synonymously referred to as RFI (Radio Frequency Interference).

electromagnetic coupling The transfer of electromagnetic energy from one circuit or system to another circuit or system. An undesired transfer is termed EMI (electromagnetic interference).

electromagnetic pulse (EMP) The generation and radiation of a very narrow and very high-amplitude pulse of electromagnetic noise. It is associated with the high level pulse as a result of a nuclear detonation and with intentionally generated narrow, high-amplitude pulse for ECM applications. In the case of nuclear detonations, EMP consists of a continuous spectrum with most of its energy distributed through the low frequency band of 3 KHz to 1 MHz.

electrostatic machine A generator which produces an electric charge by friction or electrostatic induction. One of the first of these machines was built by Cavallo around 1777. Other names associated with these devices are Wimshurst, Holtz, Toepler, Wommelsdorf, and Van de Graaff (ca. 1933).

electric wave An electromagnetic wave. Also called an Hertzian wave.

electrostatic induction a process whereby an object is charged by bringing it into proximity with another charged body.

electrostatic unit (esu) A unit of electric charge that exerts a force of 1 dyne on another unit of charge at a distance of 1 centimeter in a vacuum (cgs).

ether An hypothesized all pervasive elastic medium by which Tesla believed wireless signals were propagated by alternating compression and rarefaction.

Feedline Another term for transmission line.

field strength The magnitude of a magnetic or electric field at any point, usually expressed in terms of ampere turns per meter or volts per meter. Sometimes called field intensity and is expressed in volts/meter or dBv/meter.

fluorescent lamp A gas-filled lamp in which light is produced by ultraviolet radiation causing the fluorescence of phosphors lining the lamp's glass tube or enclosure.

foot candle A measure of light intensity on a surface being illuminated.  Defined as one lumin of light per one square foot of surface area.

frequency The rate of alteration in an electric current or electromagnetic wave, expressed in cycles per second or Hertz (Hz).

frequency hopping A spread spectrum communications technique in which a wireless transmitter and receiver are programmed to hop from frequency to frequency simultaneously.

frequency modulation (FM) A form of modulation in which the frequency of the modulated carrier wave is varied in proportion to the amplitude of the modulating wave.  In this case the phase of the carrier varies with the integral of the modulating wave. See also modulation.

frequency multiplication . . .

gauss A unit of magnetic flux density equal to 10 ^-4 weber per meter square.

generator A rotary electrical machine for producing direct current.  May also refer to an electrical alternator.

high frequency ballast 

Hertz (Hz) The unit of frequency equal to one cycle per second.

inductor A length of wire or other conductor generally wound around a cylindrical tube or framework to form a coil.

insulator A material having a high resistance to the passage of an electrical current. See also dielectric

international coulomb A unit of electric charge equal to 0.999835 coulomb. Standard coulomb prior to 1950.

isotropic antenna A hypothetical antenna which radiates or receives energy equally in all directions.

LC circuit A radio frequency electrical circuit composed of an inductor and a capacitor. An LC circuit exhibits resonance at a specific frequency which is determined by the value of the inductor and the capacitor.

Leyden jar An early form of electrical condenser or capacitor consisting of a glass container lined inside and out with metal foil.

mach number The ratio of the velocity of a body to the speed of sound in the medium that is being considered. In the atmosphere, the speed of sound varies with temperature and atmospheric pressure, hence, so does mach number.

magnifying transmitter An advanced type of Tesla electrical oscillator or Tesla coil specifically intended for wireless transmission. In addition to the primary and secondary inductors characteristic of the classic oscillator, Tesla added a third inductor known as the "extra coil." In practice, this helical resonator is physically separated from the other two coils, which comprise the master oscillator section, this in order to minimize inductive coupling between the two systems. Power from the master oscillator is fed to the lower end of the extra coil resonator through a heavy electrical conductor.  See also Tesla coil.

microvolt per meter (:V/m) A commonly used unit of field strength at a given point. The field strength is measured by locating a standard receiving antenna at that point, and the "microvolts per meter" value is then the ratio of the antenna voltage in microvolts to the effective antenna length in meters. Usually used below 100 MHz. Above 100 MHz, power density terminology is normally used.

mixer A device which utilizes its non-linear characteristics to provide frequency conversions from one frequency to another. This may be from a relatively high frequency to an intermediate frequency (IF). In this case it is known as a down-mixer. Or it may be from a lower frequency to a higher frequency, the carrier frequency, for example. In this case it is known as an upmixer. *

modulation The process whereby some characteristic of one wave is varied in accordance with some characteristic of another wave. The basic types of modulation are angle modulation, including the special cases of phase modulation and frequency modulation, and amplitude modulation.

phased array radar Radar using many antenna elements which are combined in a controlled phase relationship. The direction of the beam can be changed as rapidly as the phase relationships (usually less than 20 microseconds). Thus, the antenna typically remains stationary while the beam is electronically scanned. The use of many antenna elements allows for very rapid and high directivity of the beam(s) with a large peak and/or average power. There is also a potential for greater reliability over a conventional radar since the array will fail gracefully, one element at a time.

phase modulation The phase of the modulated carrier is varied in proportion to the amplitude of the modulating wave. See also modulation.

power amplifier (PA) An amplifier which provides high power gain to a wireless transmitter. Typical figures of merit include gain, efficiency and linearity (in amplitude and phase modulated systems) and stability. *

Ohm's law A statement of the relationship of current, voltage, and resistance in dc electrical circuits. The current in a circuit is directly proportional to the voltage and inversely proportional to the resistance. It may be expressed by any one of three equations: I = E/R , R = E/I , E = IR, where I = current, E = voltage, and R = resistance.

polyphase AC An electrical current which is generated in two or more phases each having exactly the same the same frequency. AC power is typically generated and transmitted as 3-phase current.  See also alternating current.

primary winding See transformer.

propagation In electrical practice, the travel of waves through or along a medium. The path traveled by the wave in getting from one point to another is known as the propagation path (such as the path through the atmosphere in getting from a transmitting antenna to a receiving antenna, or the path through the waveguides and other microwave devices in getting from an antenna to a receiver).

radio A form of wireless communications in which the output of the transmitter takes the form of dissipating electromagnetic radiation which spreads outward from the antenna through free space. The signal strength drops off as the square of the distance from the source of radiation. Distant radio receivers have to be very sensitive to detect signals that can measure only a few microvolts per meter in strength.

radio frequency (RF) The frequencies of the electromagnetic spectrum normally associated with radio wave propagation. Sometimes defined as any frequency at which transmission of coherent electromagnetic energy radiation is possible. *

radio frequency interference (RFI) Any induced, radiated, or conducted electrical disturbance or transient that causes undesirable responses or malfunctioning in any electrical or electronic equipment, device, or system. Same as EMI.

receiver The portion of a communications system that includes a detector and other circuitry to convert electrical signals (electric waves) to audio or data signals. It provides reception and, if necessary, demodulation of electronic signals. *

resonance A phenomenon exhibited by an electrically excited LC circuit in which a comparatively large oscillatory current flows at a certain frequency.

rotating magnetic field A circular motion from pole to pole the magnetic field in the stator of an ac induction motor. See also Egg of Columbus.

secondary winding See transformer.

slow-wave helical resonator A resonant circuit consisting of a single-layer cylindrical spiral inductor.  Usually includes capacitive end loading for tuning and, when incorporated in a high power oscillator, to prevent disruptive discharge.  The magnifying transmitter's base-driven extra coil behaves as a slow-wave helical resonator 

spectrum The distribution of power versus frequency in an electromagnetic wave.  Often used in the context of frequency allocations in reference to the frequencies allowed for a type of service out of the total available.

spectrum analyser An electronic device for automatically displaying the spectrum of the electromagnetic radiation from one or more devices. A cathode ray tube display is commonly used to display this power-versus frequency spectrum.

spurious emission Electromagnetic radiation transmitted on a frequency outside the bandwidth required for satisfactory transmission of the required waveform. Spurious emissions include harmonics, parasitic emissions, and intermodulation products, but exclude necessary modulation sidebands of the fundamental carrier frequency.

streamer A luminous electrical discharge from a high-voltage terminal traveling out into the surrounding space.  See also arc.

telautomaton The term which Tesla used to describe his remote controlled boats which were demonstrated in Madison Square Garden in New York City, and also Chicago. Developed principally as an instrument of warfare, this design concept is a direct progenitor of the modern day cruise missile. It can also be considered as having laid the ground work for robotics and the unmanned exploration of space.

teleforce Tesla's device for projecting concentrated non- dispersive energy by means of a narrow stream of metallic particles.

telegeodynamics Tesla's system for prospecting and the location of underground mineralized structures through the transmission of mechanical energy through the subsurface. Data from reflected and refracted signals can be analyzed to deduce the location and characteristics of underground formations. Additional non-mechanical responses to the initial acoustic impulses may also be detected.

terminal capacity A metallic body—usually an sphere or toroid—which is connected to the high voltage terminal of a Tesla coil, the other terminal being grounded. It is known as an elevated capacity when the Tesla coil is configured for use as a wireless transmitter in which case the terminal is mounted on the top of a pole, tower or other insulated supporting structure.

tesla Unit of magnetic flux density equal to 1 weber per meter square or 10,000 gauss.

Tesla coil Also known as the disruptive discharge coil, this is a form of electrical oscillator developed by Nikola Tesla which produces high voltage, radio frequency alternating electric current. In their first application these devices served as power supplies for experimental high frequency light bulbs. They were also used as a source of radio frequency currents in Tesla's pioneering wireless experiments, offering a superior alternative to his high frequency alternators. The classic Tesla coil consists of an air core transformer with loose coupling between the primary and secondary. The primary winding is excited by the discharge of a high voltage capacitor through a mechanical switching device known as a "break."  Vacuum-tube and solid-state circuits have been developed for use in place of the primary capacitor and break.  In a properly designed Tesla coil, the high potential appearing at the secondary's high voltage terminal is developed more or less through a process known as "resonant rise" and exceeds that which would be expected from simple ratio of transformation.  See also magnifying transmitter.

Tesla turbine A rotary engine consisting of multiple ported disks which are mounted in parallel on a shaft and placed within a cylindrical casing. In operation high velocity gases enter tangentially through a wide nozzle at the periphery of the disks, flow between them in free spiral paths to exit through central exhaust ports. The slight viscosity of the gas along with its adhesion to the faces of the disks combined to efficiently transfer the fuel's energy to the disks and on to the shaft.

transformer An electrical device consisting of two or more coils of wire placed in close proximity to each other. An alternating current applied to the first coil or "primary" sets up a time varying magnetic field which transfers energy to the "secondary" winding(s) by electromagnetic induction. Commonly used to increase or decrease voltage levels in power supply circuits. Also used for the purpose of coupling within audio and RF circuits.

transient  A high-voltage surge or spike in an electrical transmission system caused by lightning strikes to nearby transformers, overhead lines, or the ground, and which may persist for a relatively short time after the phenomenon (sometimes called ringing).  They may also result from the switching of motors, short circuits, or utility system switching.

transmitter Equipment which generates RF power to be fed to an antenna or other output interface for transmission. In modern radio equipment it consists of active components such as a modulator, driver and PA and passive components such as a TX filter. Taken together, these components impress an information carrying signal onto an RF carrier of the correct frequency by instantaneously adjusting its phase, frequency, or amplitude and provide enough gain to the signal to project it through the ether to its intended recipient. *

transmission line The electrical conductor that connects a transmitter or receiver to an antenna. Usually coaxial cable or sometimes twin lead consisting of two parallel conductors.

undamped wave See continuous wave.

Wardenclyffe Nikola Tesla's historic laboratory and wireless communications facility located about 65 miles east of New York City on the North Shore of Long Island. It was here that he worked out many of the final details for his "World System." Although the distinctive 187 foot tall tower was demolished in 1917, the sturdy 94 foot square building still stands in silent testimony to Tesla's unfulfilled dream.

Watt A measurement unit of electrical ability to perform work.

wavelength () The distance traveled by a wave in one period (the period is the time required to complete one cycle). = c / f. In the atmosphere, electromagnetic waves travel at c, the speed of light (300 million meters per second or 30 cm/nsec). At 100 kHz, one wavelength = 3000 meters, At 15 MHz, one wavelength = 20 meters.  5 GHz, one wavelength = 6 cm.

wavemeter An instrument for measuring the frequency of a radio wave. The wavemeter is a mechanically tunable resonant circuit. Below 20 GHz, the wavemeter has been replaced by the frequency counter with much greater accuracy and ease of use.

weber Unit of magnetic flux equal to the flux linking a single turn of wire, which produces in the wire an electromotive force of 1 volt when reduced to zero in 1 second. (mks).  See also gauss and tesla.

wireless Any system by which electrical energy is transmitted without wires from one location to another. The three principle methods are electrical induction, electromagnetic radiation, electrical conduction. The induction method involves the coupling of two widely separated loops of wire in much the same way as the primary and secondary windings of a transformer are linked. In the present system that we now know as "radio" the propagation of energy takes place by electromagnetic radiation. The third method—ground conduction—bears a great similarity to radio in that in both cases the transmitting element incorporates a radio frequency electrical oscillator. The difference exists in the fact that in the latter case the transmitter's output signal is sent to an underground connection rather that an elevated antenna.

World System Tesla's plan for a system to provide global wireless broadcasting, telecommunications, and a long range aid to navigation. In its more developed state he envisioned the system could be expanded to include the wireless distribution of electrical power.