Learning Event 2:
DESCRIBE THE USES OF A SIGNAL GENERATOR
1.
A signal generator is a test device which generates an alternating voltage
signal suitable for test purposes.
It is, in effect, a small radio transmitter
generating a signal of any desired frequency. The signal may be either modulated
or unmodulated and is used for the following checks or tests:
a. Alignment of tuned
circuits,
sensitivity
measurements,
and
approximate
frequency measurements.
b. For frequency measurements, its use is limited
because
it
is
not
a
frequency meter and cannot be used as a frequency standard.
2.
The signal generator is used primarily in the alignment of tuned circuits. A
signal generator is classified according to its frequency and is one of two types:
audio frequency or radio frequency.
a. Audio frequency generators produce signals with a frequency range from 20
Hz to 20kHz.
b. Radio-frequency generators produce signals covering a range of frequencies
from 10 kHz to 10 GHz.
Many radio-frequency generators have audio outputs
separately available through front panel jacks. These outputs are normally 100 and
400 Hz.
3.
When using the generator, the output test signal is coupled into the circuit
being tested, and its progress through the equipment is traced by the use of high-
impedance indicating devices such as vacuum-tube voltmeters or scopes.
In many
signal generators, calibrated networks of resistors, called attenuators, are
provided.
These are used to regulate the voltage of the output signal and also
provide correct impedance values for matching the input impedance of the circuit
under testing.
Accurately calibrated attenuators are used, because the signal
strength must be regulated to avoid overloading the circuit receiving the signal.
4.
There are many types of signal generators. They may be classified roughly by
frequency into audio signal generators, video signal generators, radio frequency
generators, frequency-modulated RF generators, and special types which combine all
of these frequency ranges.
5.
Audio signal generators.
a. Audio signal generators produce stable audio-frequency signals used for
testing audio equipment. Video signal generators produce signals which include the
audio range and extend considerably further into the RF range.
These generators
are used in testing video amplifiers and other wideband circuits.
b. In both audio and video generators, the major components include a power
supply, an oscillator, one or more amplifiers, and an output control.
Voltage
regulation circuits are necessary to ensure stability of the oscilla-
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