A dummy load is a device used to simulate an

electrical load An electrical load is an electrical component or portion of a Electric Circuit, circuit that consumes (active) electric power, such as electrical appliances and Electric light, lights inside the home. The term may also refer to the power Power con ...

, usually for testing purposes. In

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

a dummy antenna is connected to the output of a

radio transmitter In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna with the purpose of signal transmissio ...

and electrically simulates an antenna, to allow the transmitter to be adjusted and tested without radiating

radio wave Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...

s. In audio systems, a dummy load is connected to the output of an amplifier to electrically simulate a

loudspeaker A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...

, allowing the amplifier to be tested without producing sound. Load banks are connected to electrical

power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...

to simulate the supply's intended

for testing purposes.

Radio

In radio this device is also known as a dummy antenna or a

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...

termination. It is a device, usually a

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

, used in place of an antenna to aid in testing a

. It is substituted for the antenna while one adjusts the transmitter, so that no radio waves are radiated so that the transmitter does not interfere with other radio transmitters during the adjustments. (As no dummy load is ideal, however, some radiation does occur). If a transmitter is tested without a load attached to its output terminals such as an antenna or a dummy load, the power will be reflected back into the transmitter, often overheating and damaging it. Also, if a transmitter is adjusted without a load, it will operate differently as compared with a load, and the adjustments may be incorrect. The dummy load ordinarily should be a pure resistance; the amount of resistance should be the same as the impedance of the antenna or transmission line that is used with the transmitter (usually 50 Ω or 75 Ω). The radio energy that is absorbed by the dummy load is converted to heat. A dummy load must be chosen or designed to tolerate the amount of power that can be delivered by the transmitter. Typically it consists of a

attached to some type of

heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is thermal management (electronics), ...

to dissipate the power from the transmitter. The ideal dummy load provides a standing wave ratio ( SWR) of 1:1 at the given impedance. Veterinarian-grade

mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, ...

, an inexpensive form of mineral oil, is frequently used by

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

operators as coolant in RF dummy loads.

Audio

When testing

audio amplifier An audio power amplifier (or power amp) electronic amplifier, amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup (music technology), pickup, to a level that is high enough for dr ...

s, it is common to replace the

with a dummy load, so that the amplifier's handling of large power levels can be tested without actually producing intense sound. The simplest is a resistor bank to simulate the

voice coil A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. Th ...

's resistance. For loudspeaker simulation, a more complex network is more accurate, however, as actual loudspeakers are reactive and

non-linear In mathematics and science, a nonlinear system (or a non-linear system) is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathe ...

. There are many designs for loudspeaker simulators, which emphasize different characteristics of the actual speaker, such as the

's inductance, mechanical suspension compliance, and cone mass.

Power supplies

There are also dummy loads for power supplies, known as load banks. These may be used, for example, for factory and in-service testing of standby generators. A load bank may be used to stabilize a power system in case of loss of load, for example, on an isolated wind or mini-hydro plant. An electronic load (or e-load) is a device or assembly that simulates loading on an electronic circuit. It is used as substitute for a conventional ohmic load resistor. As counterpart to a

current source A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it. A current source is the dual of a voltage source. The term ''current sink'' is sometimes used for sources fed ...

, the electronic load is a current sink. When loading a current source with a fixed resistor one can set one determined load current by the connected load resistor. The characteristic of the electronic load is that the load current can be set and varied in a defined range. The load current is regulated electronically. The electronic load consumes

electric energy Electrical energy is the energy transferred as electric charges move between points with different electric potential, that is, as they move across a potential difference. As electric potential is lost or gained, work is done changing the energy o ...

and in most cases transforms it into

heat In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...

. Fans or water-cooled elements are used as coolers. Under certain conditions, energy-recycling into the public power supply system is also possible. Electronic loads are used in diverse applications, particularly for the test of

, batteries, solar and

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

s, generators. AC loads are used to test

transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...

uninterruptible power supplies An uninterruptible power supply (UPS) or uninterruptible power source is a type of continual power system that provides automated backup electric power to a load when the input power source or mains power fails. A UPS differs from a tradition ...

(UPS) or onboard power supplies. The equipment and power spectrum of such electronic loads begins with simplest circuits consisting in general of a potentiometer for current setting and a transistor circuit for power transforming. Further developed electronic loads supply several operating modes, in most cases constant current, voltage, power and resistance. Nowadays, the equipment may be controlled by a PLC or remotely by a PC. Settings and measured values such as input voltage and actual load current are indicated on a display.

References

External links

Speaker impedance
- ePanorama.net {{Analogue TV transmitter topics Electrical circuits Radio electronics

Radio

Audio

Power supplies

See also

References

Further reading

External links