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When measuring EMI performance, did you find that no matter what method you use, there are still problems that exceed the specification by a few dB? There is a way to help you meet EMI performance requirements or simplify your filter design. This approach involves modulation of the power switching frequency to introduce sideband energy and to change the narrowband noise to wideband emission characteristics to effectively attenuate harmonic peaks.
It should be noted that the overall EMI performance has not been reduced, but has been redistributed. With sinusoidal modulation, the two variables of the controllable variable are the modulation frequency (fm) and the magnitude of the power switching frequency (Δf) that you change. The modulation index (Β) is the ratio of these two variables: Β = Δf / fm The choice of modulation frequency and frequency shift are two important aspects. First, the modulation frequency should be higher than the EMI receiver bandwidth so that the receiver does not measure both sidebands at the same time. However, if the frequency you choose is too high, the power control loop may not be able to fully control this change, resulting in a change in output voltage at the same rate. In addition, this modulation can cause audible noise in the power supply. Therefore, the modulation frequency we choose cannot generally be much higher than the receiver bandwidth, but greater than the audible noise range.
Figure 3 herein compares EMI performance measurements with frequency modulation and no frequency modulation. At this point the modulation index is 4, and as we expected, the EMI performance at the fundamental frequency is reduced by approximately 8 dB. Other aspects are also important. The harmonics are smear into the frequency band corresponding to their number, ie the third harmonic extends to three times the fundamental frequency. This situation is repeated at some higher frequencies, resulting in a noise floor that is much higher than the fixed frequency. Therefore, this method may not be suitable for low noise systems. However, many systems have benefited from this approach by increasing design margins and minimizing EMI filter costs.
Dual-band WiFi module refers to the WiFi module that supports both 2.4GHZ and 5GHz bands. The dual-band WiFi module can operate in the 5Ghz band, which is much cleaner and can easily avoid interfering with each other. The advantage of 2.4G is that it has good ability to penetrate the wall, and the disadvantage is that it is easy to be disturbed. The advantages of 5G are strong anti-interference ability, wide band width, high throughput rate, and strong scalability, but the disadvantage is that 5G is only suitable for indoor small-range coverage and outdoor bridge, and the attenuation effect of various obstacles on it is much larger than 2.4g.
Dual-band WiFi module has a stronger and more stable Wifi wireless signal, higher transmission speed, and can make wireless devices more power-saving, to meet the future high-definition and big data wireless transmission needs.
When selecting a dual-frequency WiFi module, we should pay attention to these parameters of the WiFi module: size, package, frequency range, data rate, transmission rate, transmission distance, communication interface, power supply voltage, antenna interface, etc.
Dual frequency WiFi module can well meet the functional needs of users, increase the competitiveness of the product, while the WiFi module is easy to use, can shorten the user product development cycle, speed up the product market! Users can make choices according to actual needs!
Choosing a dual-band WiFi module may need to pay attention to the following points:
(1) Consider the transmission power of the dual-frequency WiFi module
The transmitting power of the WIFI module is generally about 18dBm, and the transmitting power of the high-power WIFI module is about 28dBm.
(2) Transmission rate
Consider whether the dual-band WiFi module supports MIMO technology (that is, allows multiple antennas to send and receive multiple spatial streams simultaneously)
(3) Consider the application interface that dual-band WiFi modules can provide, which is also very important.
(4) According to the requirements of the application scenario to choose the dual-band WiFi module, not the higher the configuration, the better, the application is good, excess waste!
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Shenzhen MovingComm Technology Co., Ltd. , https://www.movingcommtech.com