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The signal jammer is first and foremost the information of the shell. There are currently two types on the market: the first uses a metal casing, and the second uses a plastic casing. Usually a metal casing is used on the outside and a plastic casing is used on the inside.
There is still a little difference in the external structure of the two test room signal jammers. Signal jammers with built-in antennas usually have the antenna installed inside and consist of various electronic components. A built-in antenna signal jammer like this would look good on the outside. The signal shield of the external antenna is on the housing, and there are several ports for installing the external antenna. These interfaces represent signal shielding for different channels.