Data Sheet

Module：EWN-8258FAT1CC
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12.3 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.
12.3.1 Interface interference
When HDMI uses the 74.2MHz frequency, its 33x frequency is in the 2.4G band of BT, which
will seriously interfere with the BT signal. If the HDMI frequency is 148.5MHz, although the 16x
frequency is not in the BT band, the isolation of the frequency is not good, and the BT signal will
be interfered to some extent. If the distance between the HDMI interface and the BT module on
the PCB is less than 5cm, the HDMI output display will interfere with the BT signal, resulting in
problems such as BT connection failure and throughput drop. Therefore, keep the location of the
BT module away from the HDMI port on the hardware layout to avoid interference.
At the same time, if the BT 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 BT 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.)