# 1.4.6 Receiver blocking

The level of interference determined by the interferer’s transmit power, the antenna gains and propagation loss, is further decreased due to the receiver blocking performance for a given interferer/victim frequency separation. Details on the iRSS<sub data-renderer-mark="true">blocking</sub> calculation are given in [ANNEX 5](https://ecowiki.atlassian.net/wiki/spaces/SH/pages/494649 "https://ecowiki.atlassian.net/wiki/spaces/SH/pages/494649"):.

Note that from SEAMCAT 5.0.1 onwards, the blocking attenuation is computed at the <span data-highlighted="true" data-vc="highlighted-text"><span class="_kqswh2mm"><span class="_5pioz8co _189e1dm9 _1il9buyh _19lc184f _d0altlke" data-testid="definition-highlighter">ILT</span></span></span> frequency and that the <span data-highlighted="true" data-vc="highlighted-text">ILT</span> bandwidth is nowconsidered (see [ANNEX 8](https://ecowiki.atlassian.net/wiki/spaces/SH/pages/494660/A8+Receiver+selectivity+and+blocking+attenuation#A8Receiverselectivityandblockingattenuation-A8 "https://ecowiki.atlassian.net/wiki/spaces/SH/pages/494660/A8+Receiver+selectivity+and+blocking+attenuation#A8Receiverselectivityandblockingattenuation-A8"):). There are 3 ways to calculate the blocking response which are described in more detail in [ANNEX 8](https://ecowiki.atlassian.net/wiki/spaces/SH/pages/494660/A8+Receiver+selectivity+and+blocking+attenuation#A8Receiverselectivityandblockingattenuation-A8 "https://ecowiki.atlassian.net/wiki/spaces/SH/pages/494660/A8+Receiver+selectivity+and+blocking+attenuation#A8Receiverselectivityandblockingattenuation-A8")::

*User Defined (dB): Att<sub data-renderer-mark="true">Blocking</sub> = Block<sub data-renderer-mark="true">UD (dB) </sub>(Eq. 13)*

*Protection Ratio (dB): Att<sub data-renderer-mark="true">Blocking</sub> = Block<sub data-renderer-mark="true">PR</sub> <sub data-renderer-mark="true">(dB)</sub> + C/(N+I) <sub data-renderer-mark="true">(dB)</sub> + (N+I)/N <sub data-renderer-mark="true">(dB)</sub> - I/N <sub data-renderer-mark="true">(dB) </sub>(Eq. 14)*

*Sensitivity Mode (dBm): Att<sub data-renderer-mark="true">Blocking</sub> = Block<sub data-renderer-mark="true">Sens</sub> <sub data-renderer-mark="true">(dBm)</sub> – Sensitivity<sub data-renderer-mark="true"><span data-highlighted="true" data-vc="highlighted-text"><span class="_kqswh2mm"><span class="_5pioz8co _189e1dm9 _1il9buyh _19lc184f _d0altlke" data-testid="definition-highlighter">VLR</span></span></span></sub> <sub data-renderer-mark="true">(dBm)</sub> + C/(N+I) <sub data-renderer-mark="true">(dB)</sub> – I/N <sub data-renderer-mark="true">(dB) </sub>(Eq. 15)*

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/W7MjEAtc17C357hZ-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/W7MjEAtc17C357hZ-image.png)**Figure 12: Illustration of the blocking of the victim link receiver (i.e. total emission power of <span data-highlighted="true" data-vc="highlighted-text">ILT</span> reduced by the blocking attenuation (selectivity) function of the <span data-highlighted="true" data-vc="highlighted-text">VLR</span>**