The common modulation methods to modulate digital data to analog signals are amplitude modulation, frequency modulation, phase modulation three methods. Amplitude modulation means that the amplitude of the carrier varies with the baseband digital signal, for example, digital signal 1 is represented by a carrier output, and digital signal 0 is represented by a carrier-free output. This method of amplitude modulation is also called amplitude keying, which is characterized by easy signal realization, simple technology, but poor anti-interference ability.
Radio communication converts analog or digital signals into special analog signals to be modulated. The commonly used analog modulation methods are analog continuous wave modulation (referred to as analog modulation), digital modulationWord continuous wave modulation (referred to as digital modulation), analog pulse modulation and digital pulse modulation. According to the modulated signal form can be divided into analog modulation and digital modulation. Modulation with analog signals is called analog modulation; Modulation with data or digital signals is called digital modulation.
Amplitude Modulation (AM) In amplitude modulation, the amplitude of the carrier wave changes in response to changes in the digital signal. For example, a simple binary digital signal can be represented by two different amplitude levels, corresponding to the binary "0" and "1" respectively. When the digital signal is"When 1 ", the amplitude of the carrier will increase; When the digital signal is "0", the amplitude of the carrier is reduced.
The digital data in the computer is represented by an analog signal in the network, to be modulated, that is, to carry out a wave line transformation, or strictly speaking, a spectrum transformation, to transform the spectrum of the digital signal into a spectrum suitable for transmission in the analog channel. The basic modulation methods are amplitude modulation, frequency modulation and phase modulation. Analog data coding refers to the process of converting the digital signal generated by the sending computer into an analog quantity suitable for transmission on an analog channel.
1, it should be said that the difference between BLDC and PMSM, sometimes depends on the application. The traditional argument is that their counter electromotive force is different, BLDC is close to square wave, PMSM is close to sine wave. In terms of control, BLDC generally uses a 6-beat square wave drive to control the phase and reverse time of the square wave, while PMSM uses FOC. In terms of performance, the output power density of BLDC will be larger, because the BLDC has sufficient torqueHarmonics are used, so the harmonics of BLDC will be more serious.
2, the amplitude of the AC voltage obtained by the pulse amplitude modulation (PAM) inverter is equal to the DC voltage value (Um=Ud). Therefore, to achieve frequency conversion is also the easiest way to think of voltage change, that is, to adjust the DC voltage while adjusting the frequency. The characteristic of this method is that the frequency converter changes the Amplitude value of the voltage at the same time as changing the output frequency, so it is called Pulse amplitude Modulation, which is commonly expressed by PAM (Pulse Amplitude Modulation).
3. Usually,Pulse Modulation is divided into pulse amplitude modulation (PAM), Pulse Width Modulation (PWM) and pulse position modulation (PPM) according to the difference of pulse parameters (amplitude, width, time position) of baseband signal. Pulse code modulation (PCM) is a modulation method that processes, quantizes and codes analog signals into digital signals.
4, pulse modulation, as the name suggests, probably includes the last two modes of modulation, but more often it may refer to the change of pulse amplitude to transmit different symbolic information, such as: PAM signal. Pulse width modulation,Different symbol information is transmitted by changing the pulse duty cycle during symbol time.
5, PWM is the abbreviation of English Pulse Width ModulaTIon (pulse width modulation), a modulation mode in which the pulse width of the pulse sequence is changed according to certain rules to adjust the output and waveform. PAM is a modulation mode that changes the pulse amplitude of the pulse train according to a certain law to adjust the output and waveform. PWM is pulse width modulation, that is, continuous square waves with a certain pulse width.
6, pulse amplitude modulation (PAM) is pulseA modulation in which the amplitude of the impulse carrier varies with the baseband signal. If the pulse carrier is an impulse pulse train, then the sampling theorem discussed above is the principle of pulse amplitude modulation. In other words, the signal ms (t) obtained by sampling according to the sampling theorem is a PAM signal. However, sampling by impulse train is an ideal sampling situation, which is impossible to realize.
May be because the radio antenna installation is loose. The main causes of radio noise are battery failure. The charging system is faulty. The audio host is faulty. The radio antenna plug is improperly connected. The radio antenna feeder is faulty. Electronic interference in the harsh conditions of radio waves in broadcast stations. The radio antenna is installed loosely.
Hua Jing. According to cd2003 FM radio information, as of June 12, 2023, the model of the product is Huajing brand, the price is about 10 yuan. A radio is a device or device that receives radio broadcasts.
But CD2003 is does not include stereo frequency discrimination capability, that is, R-97OI does not have stereo reception function, which is the only disadvantage of the aircraft. In the power amplifier circuit, some machines are used by SONY CXA1622, and some machines are used by Toshiba TA7376, the performance of the two chips is similar, both use BTL mode, sound quality is good. Due to the smaller size of the R-9701 speakers, the overall sound is slightly worse than the R-9700.
But CD2003 is not included stereo frequency discrimination capability, that is, the R-97OI does not have stereo reception function, whichIs the only flaw in the machine. In the power amplifier circuit, some machines are used by SONY CXA1622, and some machines are used by Toshiba TA7376, the performance of the two chips is similar, both use BTL mode, sound quality is good. Due to the smaller size of the R-9701 speakers, the overall sound is slightly worse than the R-9700.
1, thus wireless charging amplitude modulation , Mi 9 original charger can be backward compatible with the following fast charging models wireless charging amplitude modulation , such as millet millet millet 5 and so on. Mi 9 charger is USB-A port wireless charging amplitude modulation , support USB PD needs USB-C port; In addition, the built-in protocol chip of the Mi 9 charger does not support USB PD, in summary, the Mi 9 charger does not support the USB PD protocol.
2, Mi 9 fast charge without setting, only need to use the original power adapter can beUsing fast charge, Mi 9 charging interface is Type-C, mobile phone battery capacity is 3300mAh, mobile phone support 27W wired fast charge, 20W wireless flash charge, QC0 fast charge. Mobile phone usage tips: Mi 9 can view the APP power consumption ranking, open the phone, click the gear icon, enter the system Settings page, click the battery option, click "power consumption statistics" to view the APP power consumption.
3, the millet 9's 20W wireless flash enhancement test results show that its charging speed exceeds the wireless charging amplitude modulation 18W wired fast charging, even more thanThe Mi 8's wired fast charge is faster. Lei Jun shared a comparison video in Weibo, taking the Xiaomi 8 as the experimental object, the two began to charge at the same time after running out of power, official data show that the Xiaomi 9 was fully charged in 1 and a half hours, and the Xiaomi 8 has completed 100% charging in 4 minutes.
4, the flagship version of Mi 9 Pro battery capacity increased to 4000mAh, with 10V MiPPS, PPS, PD/QC 0 and other fast charging protocols, with 45W charger and 5A line. The Mi 10 Series Mi 10 is equipped with 4780mAh battery and wireless fastCharge 30W, use 10V MiPPS, PPS, PD/QC 0, the charger is 30W and with 3A cable.
Modulation is the main function of the transmitter wireless charging amplitude modulation , modulation is for wireless charging amplitude modulation The transmission of radio communications. The function is to load the required transmission of the baseband signal onto the carrier signal and radiate out through the antenna in the form of AM waves, phase modulated waves or frequency modulated waves. Mediation is an important function of the receiver, and demodulation is for the reception of radio communication.
Signal modulation can move the spectrum of the signal to any position, which is conducive to the transmission of the signal, and make full use of the spectrum resources. For example, the antenna must be one-tenth the size of the signal or larger in order for the signal to be radiated effectively. For voice signals, the corresponding antenna size should be dozens of kilometers or more, in fact, notIt can happen. This requires the modulation process to move the signal spectrum to a higher frequency range.
Modulation is a technique in which one or more periodic carriers are mixed into a signal to be sent, often used for radio wave propagation and communication, data communication using telephone lines, and so on. According to the different modulation signals, can be divided into digital modulation and analog modulation, these different modulation, is a different method, the signal and carrier synthesis technology. The reverse process of modulation, called demodulation, is used to decode the original signal.
So people introduce modem data communication, that is, low-speed data passing throughAfter the modulation is transmitted through the radio antenna, the other side is received by the antenna, and the original data is restored by demodulation. This method is also suitable for ADSL modems with telephone line Internet access. Due to the modem, ADSL signals can be superimposed on the analog phone line, rather than having to lay a separate dedicated Internet connection line.
To overcome the problem of long-distance signal transmission, it is necessary to move the signal spectrum to the high-frequency channel for transmission through modulation. Baseband signal is the original electrical signal, generally refers to the basic signal waveform, in digital communication refers to the corresponding electrical pulse. Telemetry in wireless remote control systems and wirelessModulation in electrical technology is the baseband signal to control the parameters of the high frequency carrier (amplitude, frequency and phase), so that these parameters change with the baseband signal.
Frequency modulation is to encode information by making the instantaneous frequency of the carrier change with the signal, and the emergence of frequency modulator/makes this technology widely used in broadcasting, navigation and other equipment. The characteristic of frequency modulation is that the carrier amplitude remains unchanged and the vibration frequency changes with the signal, so it has the advantages of strong anti-interference ability, wide band/frequency hopping wave and high power utilization /, but the service radius is relatively limited.
Frequency modulation refers to the frequency of radio waves through broadcast signalsRate represents the frequency of sound, and 100 uses radio waves with a particularly high frequency, usually 88MHz to 108MHz. Amplitude modulation refers to the frequency of sound represented by the amplitude of radio waves, and radio waves of various bands can be used, usually divided into long wave (China does not have), medium wave, short wave.
It is a modulation method that makes the instantaneous frequency of the modulated wave vary with the modulated signal. The circuit to realize this modulation method is called frequency modulator, which is widely used in frequency modulation broadcasting, television sound, microwave communication, phase-locked circuit and frequency sweep meter. The basic requirements of frequency modulator are large frequency shift, good frequency modulation characteristics and parasitic amplitude modulation