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A dummy load is a device used to simulate an electrical load, usually for testing purposes. In radio a dummy antenna is connected to the output of a radio transmitter and electrically simulates an antenna , to allow the transmitter to be adjusted and tested without radiating radio waves .
An antenna analyzer measuring SWR and complex impedance of a dummy load. MFJ-269, MFJ Enterprises Inc. An antenna analyzer or in British aerial analyser (also known as a noise bridge, RX bridge, SWR analyzer, or RF analyzer) is a device used for measuring the input impedance of antenna systems in radio electronics applications.
A dummy load may be connected to the output of the transmitter to prevent it actually broadcasting, and a directional coupler, possibly together with an attenuator, used to provide a feed to the spectrum analyser. [14] The spacing in frequency between the two tones is of some significance in transmitter testing.
A dummy load may have an SWR of 1:1 but an efficiency of 0, as it absorbs all the incident power, producing heat but radiating no RF energy; SWR is not a measure of an antenna's efficiency. Radiation resistance is the part of the resistance to current caused by power lost to radiation by an antenna.
SWR is used as a measure of impedance matching of a load to the characteristic impedance of a transmission line carrying radio frequency (RF) signals. This especially applies to transmission lines connecting radio transmitters and receivers with their antennas, as well as similar uses of RF cables such as cable television connections to TV receivers and distribution amplifiers.
The input admittance (the reciprocal of impedance) is a measure of the load network's propensity to draw current. The source network is the portion of the network that transmits power, and the load network is the portion of the network that consumes power.
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A radio transmitter design has to meet certain requirements. These include the frequency of operation, the type of modulation, the stability and purity of the resulting signal, the efficiency of power use, and the power level required to meet the system design objectives. [1]
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