Signal Generator: A signal generator is a vital component in a test setup, and in electronic troubleshooting whether on a service bench or in a research laboratory. Signal generators have a variety of applications, such as checking the stage gain, frequency response, and alignment in Receivern and in a wide range of other electronic equipment.
Hence, when we say that the oscillator generates a signal, it is important to note that no energy is created; it is simply converted from a d.c. source Into a.c. energy at some specific frequency.
WORKING OF AF OSCILLATOR
The block diagram of sine and square wave AF oscillator. The heart of the generator is the Wein bridge oscillator. The signal generator is called an oscillator. A Wein bridge oscillator is used in this oscillator because this oscillator gives maximum suitable for the audio frequency range. The frequency of the oscillations can be changed varying the capacitance in the oscillator. The frequency can be changed by switching in resistors of different values.
At the output, we get either a square or sine wave shaper At the output, we get either a square or sine wave. In the sine wave mode. The signal is amplified and given to the output terminal through the attenuator. The amplitude can be set by any desired value by means of an attenuator and the magnitude control. When the function switch is in a square wave position, the oscillator output is given to a shaping circuit that converts the sinusoidal signal into a square wave signal. The square wave signal is amplified through an attenuator given to the output terminals.
The instrument generates a frequency ranging from 10 Hz to 1 MHz, continuously variable for 5 decades with overlapping ranges The output is taken through a push-pull amplifier. For low output, the impedance is 600 Ω. The square wave amplitudes can be varied from 0 - 20 V (peak).
FRONT PANEL CONTROLS OF AF SIGNAL GENERATOR
1. Function Switch: It selects either sine wave or square wave output.
2. Frequency Multiplier: It selects the frequency range over 5 decades, from 10 Hz to 1 MHz.
3. Amplitude Multiplier: It attenuates the sine wave in 3 decades, X 1, X 0.1, and X 0.01.
4. Symmetry Control: It varies the symmetry of the square wave from 30% to 70%.
5. Amplitude control: It adjusts the amplitude of the waveform.
6. Frequency Selector: It selects the frequency in different ranges and varies it continuously in a ratio of 1:11.
7. On-Off Switch: It is used for ON or OFF the device.
WORKING OF FUNCTION GENERATOR
The function generator is a versatile instrument that produces different waveforms at the output with frequencies that can be adjusted over a wide range.
The block diagram of a function generator. Here two constant current sources are used to feed the integrator circuit. The frequency control network controls the magnitudes of the output source and hence the frequency of the output.
• When the circuit is switched ON, the upper constant current source sends a constant current into the integrator and the output of the integrator output reaches a pre-determined level, the comparator changes the state i.e., the upper constant current source is cut OFF while the lower source is switched ON. This current source passes a current in the reverse direction and the voltage at the integrator output decreases to a pre-determined level, again the comparator switches ON. The lower current source is switched OFF and the upper constant current source is switched ON and the repeats.
•The rate of rise or fall of the integrator output depends upon the magnitude of the current supplied by the upper/lower constant current sources. This change in the magnitudes of these currents would change the integrator output.
• The comparator output which is used to switch over the function of the current source is of square wave shape. Lastly, the triangular wave produced by the integrator is given to a resistance diode wave shaping circuit which converts this triangular signal into a sinusoidal signal.
WORKING OF RF SIGNAL GENERATOR
A radio-frequency(RF) signal generator has a sinusoidal output with a frequency range somewhere in the 100 kHz to 40 GHz range.
The block diagram of an R.F. signal generator. It consists of a single master oscillator, designed for the highest frequency range, and frequency dividers are switched to produce lower ranges.
The lowest frequency range produced by the cascaded frequency divider (9 frequency dividers of 2: 1 ratio are used), is the highest frequency range divided by 512 29, or 67 - 156 kHz. Thus, the frequency stability of the highest range is imparted to the low-frequency ranges.
For fast coarse tuning, a rocker switch is provided, which sends the indicator gliding along the slide rule scale of the main frequency dial at approximately 7% frequency changes per second. The oscillator can then be fine-tuned by means of a large rotary switch, with each division corresponding to 0.01% of the main dial setting.
The master oscillator has both automatic and manual controllers. The availability of the motor-driven frequency control is employed for programmable automatic frequency control devices.
SPECIFICATIONS OF RF SIGNAL GENERATOR
1. Output Frequency range: 50 kHz to 150 kHz
150 kHz to 420 kHz
420 kHz to 500 kHz
500 KkHz to 1500kHz
1.5 MHz to 5 MHz
5 MHz to 15 MH
15 MHz to 80 MHz
2. Amplitude Modulation: Depth of 30%
3. Output Impedance: 202 (1µV to 10 µV) 40 Ω (100 μV )
4. Output Voltage: 50 mV
5. AF modulation: 400 Hz (or) 1 kHz
6. Power supply: 230 V, 50 Hz AC
7. External Modulation Source: Frequency 0 to 5 kHz
8. Frequency Error: < 1%
APPLICATIONS OF RF SIGNAL GENERATOR
1. RF oscillator can generate various RF voltages required for alignment and servicing of radio equipment.
2. Testing of amplifier response.
3. Adjusting of amplifier response.
4. Alignment of radio and television receivers.
5. Troubleshooting, and repairing electronic devices.
6. Checking and testing various lab experiments.
7. Generation of AM, and FM modulation waves for testing communication receivers.
8. It is used for the measurement of the gain of each stage at RF frequency.
9. It can be used to determine the distortion characteristic of an amplifier.
