Specifications

Module：EWN-8822CSS3AH
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13.4 Motherboard interference avoidance
Motherboard interference comes from: high-speed data interface (HDMI), the Operating
frequency of main chip, DDR, DC-DC power supply. The method of avoiding interference
according to the characteristics of various signals is also different. The main methods of
interference avoidance include :
1. keeping away from the source of interference;
2. Adding shields to avoid interference leakage;
3. Reasonable layout to eliminate interference.
13.4.1 Interface interference
When HDMI uses the 74.2MHz frequency, its 33x frequency is in the 2.4G band of Wi-Fi,
which will seriously interfere with the Wi-Fi signal. If the HDMI frequency is 148.5MHz, although
the 16x frequency is not in the Wi-Fi band, the isolation of the frequency is not good, and the
Wi-Fi signal will be interfered to some extent. If the distance between the HDMI interface and the
Wi-Fi module on the PCB is less than 5cm, the HDMI output display will interfere with the Wi-Fi
signal, resulting in problems such as Wi-Fi connection failure and throughput drop. Therefore,
keep the location of the Wi-Fi module away from the HDMI port on the hardware layout to avoid
interference.
At the same time, if the Wi-Fi antenna is built-in the motherboard, its placement must also
be carefully considered to be far from the interface interference. If the antenna is placed in an
incorrect position, even if the module is shielded, the interference signal is coupled through the
antenna, which will eventually result in a lower Wi-Fi throughput. (Note: In addition to
interference, the placement of the internal antenna should also evaluate the effect of the metal
interface, motherboard, and housing material on the antenna impedance.)