SEM (Spectrum Emissions Mask)

SEM stands for Spectrum Emissions Mask, and it refers to a graphical representation of the allowed power levels of an electromagnetic signal across different frequencies. It is used to define the spectral characteristics and limits of electromagnetic emissions from a device or system, ensuring that they comply with regulatory standards and do not cause interference with other devices or services.

The SEM graph typically consists of two axes: frequency and power level. The frequency axis represents the range of frequencies over which the emissions are measured, usually displayed in Hertz (Hz) or kilohertz (kHz) to gigahertz (GHz) depending on the application. The power level axis represents the allowed maximum power level of the emissions at each frequency, usually displayed in decibels (dB) or milliwatts (mW).

The SEM is usually defined by regulatory bodies or standards organizations to establish the limits of permissible emissions for specific frequency bands. These standards vary depending on the type of application, such as radio communication, wireless devices, or industrial equipment. Compliance with these standards ensures that devices can coexist without causing harmful interference or violating regulatory requirements.

To create an SEM, the emissions from a device or system are measured using specialized equipment such as spectrum analyzers. The measurements are taken across the relevant frequency range, and the power levels are recorded. These measurements are then compared against the limits specified in the relevant standards.

The SEM graph displays the maximum allowable power levels at each frequency. If the measured emissions fall below the specified limits, the device or system is deemed to be compliant. However, if the emissions exceed the limits, further measures may be necessary, such as implementing filtering or shielding techniques to reduce the emissions and bring them within the acceptable range.

SEM is crucial in ensuring efficient and reliable operation of various wireless systems and devices, as it helps prevent interference between different services operating in the same frequency bands. It allows regulators to enforce standards and manage spectrum allocation effectively, ensuring that different users can coexist without compromising the performance of their respective systems.

In summary, SEM (Spectrum Emissions Mask) is a graphical representation of the allowed power levels of electromagnetic emissions across different frequencies. It defines the limits and spectral characteristics of emissions to ensure compliance with regulatory standards and prevent interference with other devices or services.