How to choose the carrier frequency of the modulated signal? It s tricky 30

If the modulation signal is v = v cos t and the carrier is vc = vccos ct, as shown in the figure below. Write the ruler key to the expression of the FM signal.

vfm, write the expression of Zen Trap renting out the instantaneous frequency offset (t) and instantaneous offset (t).

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A carrier wave is a specific frequency of non-bad jujube line radio waves, measured in Hz, which is an electromagnetic wave that is modulated in terms of frequency, amplitude modulation, or phase to transmit language, **, image, or other signals.

The carrier frequency is in the process of signal transmission, not to transmit the signal directly, but to load the signal on a fixed frequency wave, this process is called loading, such a fixed frequency. Strictly speaking, it is to modulate a lower signal frequency to a relatively higher frequency, and the higher frequency modulated by the low frequency is called the carrier frequency, also called the fundamental frequency.

Expansion and Demolition Materials:Applications of Carrier Frequency:

1. a frequency converter;

2. a generator;

3. No position sensor.

Encyclopedia - Carrier.

Encyclopedia - Carrier frequency.

It is usually a high-frequency sinusoidal signal or a pulse signal.

As a carrier, this carrier is called a carrier signal;

Use the signal to be transmitted to change a certain parameter of the carrier signal, such as amplitude.

Frequency, phase. This signal is used to change a certain parameter of the carrier signal is called a modulated signal;

What needs to be transmitted in the measurement and control system is the measurement signal, which is usually used as the modulation signal. A modulated carrier signal is called a modulated signal.

Concepts of modulated signal, carrier signal, modulated signal:

1.A modulated signal is a low-frequency signal that is transformed from the original information, that is, the information to be used is loaded onto the transmitted waveform. For example.

The signal emitted by the computer that uses the ** online network is a high-frequency digital signal.

The digital signal is loaded onto the audio signal in the ** line to complete the modulation. However, sometimes the modulated signal is generally referred to as a modulated signal;

2.The carrier signal is to load the ordinary signal (sound, image) to a certain frequency of high-frequency signal, when there is no high-frequency signal loaded with the ordinary signal, the amplitude of the high-frequency signal is fixed, and the amplitude changes with the change of the ordinary signal after loading;

3.Signals that carry useful information.

Loading useful information into a signal that can be easily transmitted is called a modulated signal.

In the process of frequency modulation, the higher the amplitude of the modulated signal, the smaller the bandwidth of the carrier wave.

In wireless transmission, the signal is radiated into space through an antenna in the form of a high resistance to electromagnetic waves. In order to obtain a high radiation efficiency, the size of the antenna should generally be greater than a quarter of the wavelength of the transmitted signal. Baseband signals, on the other hand, contain longer wavelengths of lower frequency components, making the antenna too long to achieve.

By modulating, moving the spectrum of the baseband signal to a higher carrier frequency can greatly reduce the size of the radiating antenna. In addition, modulation can move multiple baseband signals to different carrier frequencies to realize channel multiplexing and improve channel utilization.

Finally, modulation can expand the signal bandwidth, improve the anti-interference and anti-fading ability of the masking system, and improve the signal-to-noise ratio of transmission. The increase in signal-to-noise ratio comes at the expense of the bandwidth transmitted. Therefore, in the communication system, choosing the right modulation method is the key.

The purpose of the modulation is threefold:

1) It is convenient for wireless transmission and reduces the antenna size;

2) Frequency division multiplexing to improve communication capacity;

3) Improve the anti-interference ability of the signal.

In order to make full use of the channel capacity and meet the different needs of users, different modulation methods are used for communication signals. With the rapid development of electronic technology and the continuous improvement of users' requirements for information transmission, the modulation mode of communication signals has undergone a development process from analog to digital, from simple to complex.

Frequency modulation refers to the process of using modulated signals to control the frequency change of high-frequency carrier signals.

The corresponding amplitude modulation method is to represent the information through the change in the amplitude of the carrier, while its frequency remains the same. The excitation uses the different frequencies of the carrier waves to express different information. The process of modulation is also the process of pure spectrum conversion of frequency script, which must be completed with nonlinear components.

The magic of nonlinear devices is that they can obtain the power efficiency and functions that conventional devices cannot achieve.

Difference Between FM and Amplitude Modulation.

1) Frequency modulation is stronger than amplitude modulation anti-interference ability.

The influence of various external interference, processing industry and celestial power interference on the modulated wave is mainly manifested in the generation of parasitic amplitude modulation and the formation of noise. The FM system can use the method of limiting to eliminate the parasitic amplitude modulation caused by interference. However, the amplitude of the amplitude modulated signal in the amplitude modulation system is variable, so the amplitude limiting cannot be used, and it is difficult to eliminate external interference.

In addition, the larger the signal-to-noise ratio of the signal, the stronger the anti-interference ability. The signal-to-noise ratio of the demodulated signal is related to the modulation coefficient, and the larger the modulation coefficient, the greater the signal-to-noise ratio. Because the FM coefficient is much larger than the amplitude modulation coefficient, the signal-to-noise ratio of the FM wave is high, and the interference noise in the FM broadcast is small.

2) Frequency modulated wave ratio amplitude modulated frequency bandwidth.

The frequency band width is related to the modulation coefficient, that is, the modulation coefficient is large, and the frequency bandwidth is wide. In frequency modulation, the frequency modulation coefficient is often greater than 1, and the amplitude modulation coefficient is less than 1, so the frequency band width of the frequency modulation wave is much larger than that of the amplitude modulation wave.

3) The power utilization rate of the frequency modulation system is greater than that of the amplitude modulation system.

In the total transmitting power, the side-frequency power is the effective power of transmitting the modulation signal, and the side-frequency power is related to the modulation coefficient. Since the frequency modulation coefficient m is greater than the amplitude modulation coefficient m, the power utilization rate of the frequency modulation system is higher than that of the amplitude modulation system.

The center frequency of the FM signal BAI is. Carrier frequency. DU signal wave in addition to DC, zhi

Like a sine wave, a square wave dao, a triangle wave, or a number.

The reply signal and the analog signal are all voltages (currents) in both directions. The signal wave is the center frequency of the modulated wave, according to the voltage (current) in the positive and negative directions of the signal waveModulates to a high or low frequency offset.

You should know that according to the working principle of the FM signal, the frequency of the signal wave will not pull down the carrier frequency, except for a negative DC signal, other AC signals will only make the center frequency of the FM signal swing up and down at a certain frequency offset. That is, it works on a certain bandwidth.

No, the frequency of the BAI signal wave will not pull down the DU frequency of the carrier, zhi

Except for a negative DC signal DAO, other internal AC signals will only make the center frequency capacitance of the FM signal swing up and down at a certain frequency offset. That is, it works on a certain bandwidth.

Frequency modulation, the full name is "frequency modulation". A modulation method that makes the instantaneous frequency of the carrier wave change according to the change law of the desired transmitted signal. It is a modulation method that causes the instantaneous frequency of the modulated wave to change with the modulated signal.

The circuit that realizes this modulation method is called a frequency modulator, which is widely used in FM radio, television accompaniment, microwave communication, phase-locked circuit and frequency sweeper. The basic requirements for the frequency modulator are large frequency modulation shift, good frequency modulation characteristics, and small parasitic amplitude modulation. The radio waves generated by the frequency modulation method are called frequency modulation waves, and their basic characteristics are that the oscillation amplitude of the carrier remains unchanged, and the oscillation frequency changes with the modulation signal.

Frequency modulation (FM) means that the frequency of the high-frequency carrier is not a constant, but a modulation method that changes within a certain range with the modulated signal, and its amplitude is a constant. On the other hand, amplitude modulation means that the frequency of the carrier frequency is constant, and its amplitude varies with the modulated signal.