Seektronics

  Description of the phenomenon.   A plastic enclosure product with an I/O cable was found to exceed the radiation emission limit when conducting the radiation emission test specified in the EMC standard, specifically at 160 MHz. the cause of its radiation exceedance needs to be analyzed and appropriate countermeasures are given.     Reason Analysis   This product has only one PCB, which has a crystal with a frequency of 16MHz. It can be seen that the 160MHz radiation should be related to the crystal (Note: it does not mean that the radiation exceeds the standard is caused by the direct radiation of the crystal, may be multiplier generated). Figure 1 shows the product's local PCB layout, from Figure 1, it is clear that the 16MHz crystal is arranged right at the edge of the PCB.   Figure 1 The product's local PCB layout of the actual diagram   In signal lines or high-speed devices and the laboratory between the reference grounding plate, there is an electric field distribution o