The signal generated by the signal generator is often used to replace the actual signal of the front-end circuit in the circuit, providing an ideal signal for the back-end circuit. Since the characteristic parameters of signal source signal can be set manually, it can easily simulate the signal with different characteristics under various circumstances, which is especially useful for product development and circuit experiment. In circuit testing, we can measure and compare the input and output signals to determine whether the function and characteristics of the signal processing circuit meet the design requirements. For example, a signal generator is used to generate a sinusoidal wave signal with a frequency of 1kHz and input it to a measured signal processing circuit (the function is sinusoidal wave input and square wave output). At the output end of the tested circuit, an oscilloscope can be used to check whether the square wave output meets the design requirements. The high-precision signal generator can also be used as a standard signal source (reference source) in the field of measurement and calibration, and the instrument to be calibrated is calibrated according to the reference source.It can be seen that signal generator can be widely used in electronic research and development, maintenance, measurement, calibration and other fields.
For amateurs, the most common use of signal generators is to measure the sensitivity of radio stations and walkie-talkies. Many HAM people believe that it is most effective to use a comprehensive tester to test the sensitivity of a walkie-talkie. In fact, two functions of the comprehensive tester, namely, signal generator and ratio meter, are mainly used to test the sensitivity of a walkie-talkie. The signal generator emits the signal with the same modulation mode as the walkie-talkie (generally FM or AM), and then gradually reduces the amplitude (intensity) of the output signal, and at the same time, monitors the noise level of the walkie-talkie audio output through the signal-nabimeter. When the ratio between the effective signal and noise of the interphone output is degraded to a certain extent (the standard S/N=12dB for the sensitivity test of the interphone), the level value of the output of the signal generator is equal to the measured sensitivity of the interphone. In this test, the signal generator simulates the actual air signal received by the walkie-talkie, and the simulated signal strength can be manually controlled and adjusted.
Some HAM does not have a signal generator on hand, so the sensitivity of the tuning radio can only rely on listening to the actual signal in the air as a reference.This is obviously not as convenient as using a signal generator. The sensitivity of the walkie-talkie is measured by a synthesizer or signal generator. The standard connection method is: the signal output of the signal generator is connected to the antenna input end of the walkie-talkie through a cable, and the audio output end of the walkie-talkie is connected to the audio input end of the synthesizer or the sinnabometer. The author in some walkie-talkie maintenance site to see, measuring the sensitivity of walkie-talkie, only connect the signal generator, and then through listening to the sound quality of walkie-talkie speakers to roughly judge the signal-to-noise ratio, which is obviously not standard. In addition, we also need to pay attention to the difference in test standards, that is, the expected signal-to-noise ratio threshold of the output audio of the walkie-talkie is different, such as S/N=10dB or S/N=20dB, even though the sensitivity value measured by the same walkie-talkie is different. Associated with some walkie-talkie technology in the "noise open sensitivity", "available sensitivity" and other names, in fact, are using different test standards.The sensitivity values obtained by different test criteria are not comparable to each other.
Signal generator can be used to adjust the sensitivity of radio station and walkie-talkie, its basic principle is to make the filter channel in the walkie-talkie receiving channel to minimize the attenuation of useful signal transmission, so that the walkie-talkie has a higher sensitivity, which is more widely used in some amateur radio frequency modification and homemade radio.The signal generator also plays the role of simulating air signals. The signal generator also plays the role of simulating air signals. If walkie-talkie S table itself has received signal strength or test point, signal generator can be used to enter a table indicating the intensity of about 30% of the machine signal (easy to see how to adjust the change effect), and then according to the intercom service manual instructions, adjust the receiving tank circuit, make the signal indicates to the largest, if appear in the process of adjusting signal table with table, can again turn signal amplitude of the signal generator. Generally, in order to ensure the sensitivity of the whole frequency band, multiple frequency points at the high end, low end and center of the target frequency band need to be used as reference points for "unified tuning" on average. For the walkie-talkie without signal strength indication feedback, the receiver channel can only be adjusted by monitoring the improvement and deterioration of the signal to noise ratio under the condition of low SNR. In fact, in addition to adjusting the receiver sensitivity of the walkie-talkie, the signal generator can also be used to adjust the radio and television, as long as the signal generator can produce the same type of signal.
Signal generator can be used to find radio, walkie-talkie receiver channel fault. The basic principle is: from the front stage to the back stage, measure each stage of amplifier and filter in the receiving path one by one, and find out which stage of amplifier circuit does not reach the large amount of amplifier or which stage of filter circuit attenuates too much. Signal generator plays the role of standard signal source. The signal source inputs a signal of known amplitude at the antenna input end of the walkie-talkie, and then measures the gain situation step by step from the antenna input port through the uhf voltmeter or the oscilloscope with high enough frequency, finds out the unit with abnormal gain, further checks, and finally identifies the parts with faults.
Signal generators can be used to calibrate filters, typically bandpass filters and duplexers used in radio stations. The signal generator is one of the main functional parts of the network analyzer and frequency sweeper, which are ideal instruments for measuring filter. In the absence of these advanced instruments, the signal generator can barely debug the filter with the help of high-frequency voltage measurement tools, such as ultra-high frequency millivolt meter, oscilloscope with high enough frequency, measurement receiver, etc. The basic principle is to measure the attenuation of the signal inside and outside the band pass frequency band of the filter. The signal generator plays the role of standard signal source. The signal generator generates a relatively strong known frequency and amplitude signal, which is INPUT from the INPUT end of filter or duplex to measure the signal attenuation at the output end. The band-pass filter requires the attenuation to be as small as possible in the band and as large as possible outside the band, while the notch filter is just the opposite. The larger the frequency attenuation of the notch, the better. Because the ordinary signal generator is a fixed single-point frequency transmission, so the test filter needs to use multiple test points to "tune". If there is a sweep signal source and a complete spectrum analyzer, the full frequency characteristics of the filter can be graphically seen, which is very convenient for debugging.