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radio transmitter design
A radio transmitter is an electronic device which, when connected to an antenna, produces an electromagnetic signal such as in radio and television broadcasting, two way communications or radar. Heating devices, such as a microwave oven, although of similar design, are not usually called transmitters, in that they use the electromagnetic energy locally rather than transmitting it to another location.
==Design issues==
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.〔Rudolf F. Graf, William Sheets, ''Build Your Own Low-Power Transmitters: Projects for the Electronics Experimenter'' Newnes, 2001 ISBN 0750672447,
page 2〕 High-power transmitters may have additional constraints with respect to radiation safety, generation of X-rays, and protection from high voltages.〔Ronald Kitchen, ''RF Radiation Safety Handbook'', Butterworth Heinemann 1993, ISBN 0 7506 1712 8 Chapter 10〕
Typically a transmitter design includes generation of a carrier signal, which is normally〔some spread spectrum systems use pulses or sets of orthogonal wave forms〕 sinusoidal, optionally one or more frequency multiplication stages, a modulator, a power amplifier, and a filter and matching network to connect to an antenna. A very simple transmitter might contain only a continuously running oscillator coupled to some antenna system. More elaborate transmitters allow better control over the modulation of the emitted signal and improve the stability of the transmitted frequency. For example the Master Oscillator-Power Amplifier (MOPA) configuration inserts an amplifier stage between the oscillator and the antenna. This prevents changes in the loading presented by the antenna from altering the frequency of the oscillator.〔Joseph J. Carr ''Microwave and Wireless Communication Technology'', Newnes, 1997 ISBN 0750697075 page 339-341〕
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