Editing Signal generator (section)

==== Analog signal generators ====
[[File:E8257D PSG Analog Signal Generator.jpg|right|400px|thumb|An analog RF signal generator]]
Analog signal generators based on a sine-wave oscillator were common before the inception of digital electronics, and are still used. There was a sharp distinction in purpose and design of radio-frequency and audio-frequency signal generators.

;RF
RF signal generators produce [[continuous wave]] radio frequency signals of defined, adjustable,  amplitude and frequency. Many models offer various types of analog modulation, either as standard equipment or as an optional capability to the base unit. This could include [[Amplitude modulation|AM]], [[Frequency modulation|FM]], [[Phase modulation|ΦM (phase modulation)]] and [[pulse modulation]]. A common feature is an [[Attenuator (electronics)|attenuator]] to vary the signal’s output power. Depending on the manufacturer and model, output powers can range from −135 to +30&nbsp;dBm. A wide range of output power is desirable, since different applications require different amounts of signal power. For example, if a signal has to travel through a very long cable out to an antenna, a high output signal may be needed to overcome the losses through the cable and still have sufficient power at the antenna. But when testing receiver sensitivity, a low signal level is required to see how the receiver behaves under low signal-to-noise conditions.

RF signal generators are available as benchtop instruments, rackmount instruments, embeddable modules and in card-level formats. Mobile, field-testing and airborne applications benefit from lighter, battery-operated platforms.  In automated and production testing, web-browser access, which allows multi-source control, and faster frequency switching speeds improve test times and throughput.

RF signal generators are required for servicing and setting up [[radio receiver]]s, and are used for professional RF applications.

RF signal generators are characterized by their frequency bands, power capabilities (−100 to +25&nbsp;dBc), single side band phase noise at various carrier frequencies, spurs and harmonics, frequency and amplitude switching speeds and modulation capabilities.

;AF
Audio-frequency signal generators generate signals in the audio-frequency range and above. An early example was the [[HP200A]] audio oscillator, the first product sold by the [[Hewlett-Packard|Hewlett-Packard Company]] in 1939. Applications include checking frequency response of audio equipment, and many uses in the electronic laboratory.

Equipment [[distortion]] can be measured using a very-low-distortion audio generator as the signal source, with appropriate equipment to measure output distortion harmonic-by-harmonic with a [[Spectrum analyser|wave analyser]], or simply [[total harmonic distortion]]. A distortion of 0.0001% can be achieved by an audio signal generator with a relatively simple circuit.<ref>[http://www.waynekirkwood.com/Images/pdf/Cyril_Bateman/Bateman_Notes_Cap_Sound_1.pdf Capacitor Sounds 1 - Low Distortion (sub 1PPM ) 1 kHz Test Oscillator, C Bateman, Electronics World July 2002, expanded March 2003]. Description, measurements, circuit, and PCB layout</ref>