Standard sources of ac energy, both audio frequency (af) and radio frequency (rf), are often used in
the maintenance of electronic equipment. These sources, called SIGNAL GENERATORS, are used to test
and align all types of transmitters and receivers. They are also used to troubleshoot various electronic
devices and to measure frequency.
The function of a signal generator is to produce alternating current (ac) of the desired frequencies
and amplitudes with the necessary modulation for testing or measuring circuits. (Modulation was
discussed in NEETS, Module 12, Modulation Principles.) It is important that the amplitude of the signal
generated by the signal generator be correct. In many signal generators, output meters are included in the
equipment to adjust and maintain the output at standard levels over wide ranges of frequencies.
When using the signal generator, you connect the output test signal into the circuit being tested. You
can then trace the progress of the test signal through the equipment by using electronic voltmeters or
oscilloscopes. In many signal generators, calibrated networks of resistors, called ATTENUATORS, are
provided. You use attenuators in signal generators to regulate the voltage of the output signal. Only
accurately calibrated attenuators can be used because the signal strength of the generators must be
regulated to avoid overloading the circuit receiving the signal.
Q-3. In signal generators, what device is used to regulate the voltage of the output signal?
There are many types of signal generators. They are classified by use and the frequency range
covered as AUDIO-FREQUENCY (AF) GENERATORS, VIDEO SIGNAL GENERATORS, RADIO-
FREQUENCY (RF) GENERATORS, FREQUENCY-MODULATED RF GENERATORS, and other
special types, which combine frequency ranges.
AUDIO AND VIDEO SIGNAL GENERATORS
AUDIO SIGNAL GENERATORS produce stable af signals used for testing audio equipment.
VIDEO SIGNAL GENERATORS produce signals that include the audio range and extend into the rf
range. These signal generators are used to test video amplifiers and other wideband circuits. In both audio
and video signal generators (figure 5-5), major components include a POWER SUPPLY, an
OSCILLATOR (or oscillators), one or more AMPLIFIERS, and an OUTPUT CONTROL.
Figure 5-5.Af and video signal generator block diagram.