Wobbulator

A sweep generator (also wobbler wobbler, sweep generator ) is an electronic device for the production of ( wobble ) oscillations, the frequency generated (mostly high frequency between 0.1 and 1000 MHz ) varies cyclically between two adjustable end values ​​. The simpler loanword Wobbler has the German terms almost completely displaced.

Use

Through a combination with other instruments, the frequency-dependent behavior of a test object (speakers, amplifiers, filters, circuit, cable ) can be measured and graphed.

In telephone and Telegrafiebereich simple Wobbler be treated as the ringing detector at by measuring ( by ring ) used by two-wire lines.

Construction

Early sweep generators reached the cyclic variation of its output frequency to mechanically by a motor-driven frequency-determining element ( variable capacitor, variometer coil). Soon the VCOs were called for lower frequencies voltage controlled oscillator circuits (Voltage Controlled Oscillators ) are used, while the mechanical tuning could keep in the microwave range even longer, because some components could not process the necessary frequencies. The first VCO circuits realized a variable reactance as the frequency-determining element by shifting the operating point of an electron tube. From the early 1970s, took over capacity diodes this function for very high frequencies come YIG oscillators are used.

The change of the frequency is controlled by a separate slow oscillator, usually a ( so-called after the shape of its output signal) ramp - the output voltage increases linearly up to a maximum value and then returns in a short time returns to the initial value - or a generator, which generates a low-frequency sinusoidal voltage.

There often is a diagram with logarithmic frequency scale is desired, many wobbler includes a circuit which is deformed in accordance with the sawtooth signal exponentially, before it is fed to the VCO.

In addition, many sweep generators have fixed adjustable marker generator whose frequency is mixed with the set frequency. Thus arise within the waveform markers.

Modern RF synthesizers generate their output frequency by mixing different frequencies, the frequency is derived by means of PLL control loops of high-precision reference oscillators. Virtually all such devices are digitally controlled and allow to realisiseren a sweep through program control of the target frequency.

Now also with a " tracking " equipped spectrum analyzers are used for Wobbelmessungen.

Many function generators also contain a sweep.

Measurement

The output of the sweep generator is suitably connected to the input of the measuring object, the signal at the output of the measuring object is possibly amplified and processed for display ( rectify, logarithms ). For the measurement of non-electrical signals corresponding transducer come together with the measured object is used ( eg a microphone for wobbling of speakers).

To display or recording an oscilloscope is used, the horizontal deflection is synchronized with the sweep. In the simplest case, the tuning voltage of the VCO is connected to the sweep generator with the X- channel of the oscilloscope. To suppress an interfering second representation of the result, which arises during fast reverse, the VCO voltage, have some sweep generators via an output on which the return is applied a pulse; of the beam over the Z input (brightness ) of the oscilloscope dark controls.

Especially when measuring narrowband ( filters) objects, the frequency must be swept slowly so as not to distort the measurement result. This, however, display on the oscilloscope starts to flicker badly or is it even only a slowly moving point visible. Thus the entire transmission curve can be represented ( DSO) storage CRTs have therefore before advent of digital storage oscilloscopes used, the stored image lasted a few seconds and could be photographed for example. There were also complete Wobbelmessplätze that a sweep generator combined with a suitable display device, such as the well-known series " Polyskop SWOB " from Rohde & Schwarz.

For low frequency measurements was the use of an XY recorder in question, which by the advent of digital technology is now also obsolete - the results are recorded with the DSO or computer and displayed graphically.

Applications

• Amplitude response of the gain / attenuation of a circuit ( amplifiers, filters, attenuators ) or component (transistor, resonant circuit, transformer, line ) as a function of frequency (the classic " sweep " )
• Detection of S-parameters (evaluation by vector analyzer )
• Speaker measurement ( the course of the sound pressure versus frequency, resonance frequency)