Tone generator

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A tone generator , also known as a tone frequency generator , is a signal generator that usually generates a sinusoidal electrical signal in the low frequency range.

The most common embodiments are laboratory devices with adjustable levels and frequencies, or user software for PCs, as well as small fixed-frequency devices for test purposes.

Layout and function

With laboratory devices, both the frequency and the amplitude can be adjusted in order to be able to adapt the output signal to the requirements.

Such laboratory devices used to work on the basis of superimposed frequencies , that is, one mixed a fixed and an adjustable frequency in the high frequency range to obtain the low frequency. One representative is the beat buzzer SIT BN 40341 ​​(20 Hz to 20 kHz, 1… 2% distortion factor ) from Rohde & Schwarz from 1958. A typical advantageous feature of these devices was the sweeping of the low frequency range without range switching.

Vienna bridge generators were later built with which very low harmonic sine waves could be achieved. Examples are the type GF2 (16 Hz to 25 kHz) from Clamann & Grahnert / Dresden and the type GF22 (2 Hz to 20 kHz, 0.1% distortion factor) from the successor company VEB Präcitronic from 1970.

Today periodic signals with high frequency accuracy and resolution are digitally synthesized using the DDS process . The sinusoidal oscillation is generated using an algorithm or a table of values ​​using a digital-to-analog converter . The fineness of the discrete values ​​( quantization error ) and the continuity of the signal course are quality criteria of such sine wave generators. The integrated circuit AD9835, for example, has a permanently stored sine value table with 4096 values ​​(12 bits), which are output one after the other via a 10-bit digital-to-analog converter for each period.

For test and signaling purposes, small fixed frequency transmitters without special requirements for the signal quality are used, which emit a constant frequency (e.g. 800 Hz or other standard frequencies ) with a constant signal level (e.g. 0 dBV, i.e. 1 V).

A special form are wobble generators that can continuously run through their entire frequency range in a time interval. The time interval, frequency range and level can be set within wide limits. Historical wobble generators worked electromechanically, with a motor operating the frequency adjustment.

Tone generator signals can also be generated on the PC by a sound card controlled by a suitable computer program (e.g. Audacity ) . Also, smartphones are to produce a defined frequency with a corresponding additional software capable of tones.

commitment

Frequency response , recorded by means of a tone generator and level meter

Audio frequency generators are used for test and measurement purposes in the low frequency range, u. a. in transmission technology , acoustic measurement technology and electroacoustics . They are used in combination with a level meter.

In the simplest case, a fixed frequency transmitter can be used to determine whether its measuring tone is running through a sound transmission system or a cable network with the desired level and whether this is basically functional.

Adjustable generators also allow the measurement of the frequency response of a transmission system by recording several levels at different frequencies over the frequency range.

By comparing the input and output waveforms e.g. B. an audio amplifier whose distortion factor can be determined.

Tone generators with a defined sound level and headphones are used to examine the hearing ability .

In connection with a level measurement, wobble generators enable automatic frequency response recording.


literature

  • Telefunken Laborbuch Volume 2, 5th edition, publisher AEG-Telefunken, published by Franzis-Verlag G. Emil Mayer KG, Munich

Web links

Individual evidence

  1. ↑ https://www.radiomuseum.org/r/rohde_schwebungssummer_sit_bn_40341.html Presentation of the beat buzzer SIT BN 40341 ​​at radiomuseum.org , accessed on Jan. 17, 2019
  2. ↑ http://www.historische-messtechnik.de/downloads/rs-sit-bn-40341-1957- Handbuch.pdf Rohde & Schwarz: Description of the beat buzzer type SIT BN 40341 , with a detailed description of the function, accessed on Jan. 17, 2019
  3. ↑ http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Pracitronic/GF22.pdf Operating instructions for the GF22 tone generator including circuit diagram, accessed on Jan 17, 2019
  4. ↑ https://www.radiomuseum.org/r/praecitron_rc_generator_gf_22_gf22.html Presentation of the GF22 at radiomuseum.org , accessed on Jan. 17, 2019
  5. ↑ https://www.analog.com/media/en/technical-documentation/data-sheets/ad9835.pdf data sheet of the AD9835
  6. ↑ http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Pracitronic/GF72.pdf Low-frequency wobble transmitter GF72, accessed on Jan. 17, 2019