Sweep Frequency Generator: Function, Features & Applications

Sep 1, 2024

—

John Mulindi

in Electrical & Electronics Measurements

Contents

1 Function & Features of a Sweep Frequency Generator
2 Sweep Frequency Generator Applications

Function & Features of a Sweep Frequency Generator

A special type of signal generator which generates a sinusoidal output whose frequency is automatically varied or swept between two chosen frequencies is referred to as sweep frequency generator. One complete cycle of the frequency variation is termed as a sweep. The rate at which the frequency is varied can either be linear or logarithmic, depending upon the design of a specific instrument. Nevertheless, the amplitude of the signal output is designed to remain constant over the entire frequency range of the sweep.

The figure below illustrates a block diagram of an electronically tuned frequency generator:

Fig: Block diagram of an electronically tuned sweep frequency generator

As shown in the diagram above, the main component of a sweep frequency generator is a master oscillator, normally an RF type, with several operating ranges which are chosen by range switch.

The frequency of the output signal generator may be varied either mechanically or electronically. In the mechanically varied models, the frequency of the output signal of the master oscillator is varied (tuned) by a motor driven capacitor. On the other hand, in the electronically tuned models, the frequency of the master oscillator is kept fixed and a varying frequency signal is produced in another oscillator referred to as the voltage controlled oscillator (VCO). The VCO contains an element whose capacitance depends upon the voltage applied across it. This element is used for varying the frequency of the sinusoidal output of the VCO. The output of the VCO is then combined with the output of the master oscillator in a special electronic device called the mixer. The output of the mixer is sinusoidal, whose frequency depends on the differences of frequencies of the output signals of the master oscillator and VCO. For instance, if the master oscillator frequency is fixed at 10.00 MHz and the variable frequency is varied between 10.01 MHz to 35 MHz, the mixer will give sinusoidal output whose frequency is swept from 10 kHz to 25 MHz.

Sweep Frequency Generator Applications

Sweep frequency generators are primarily used for measurement of responses of amplifiers, filters and other electrical components over various frequency bands. The frequency range of a sweep frequency generator typically extends over three bands:

0.001 Hz – 100 kHz (low frequency to audio).
100 kHz – 1500 MHz (RF range).
1 – 200 GHz (microwave range).

Sweep generators may also be used for checking and repairing amplifiers used in radar receivers and TVs.

Measuring bandwidth over a wide frequency range using a manually tuned oscillator consumes considerable time and effort, but with the use of a sweep frequency generator, a sinusoidal signal that is automatically swept between two selected frequencies can be applied to the circuit under test and its response against frequency displayed on an oscilloscope or X-Y recorder, thus reducing the measurement time and effort.

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