page_title: RF chain
section_title: Tangential sensitivity
hierarchical_section_title: RF chain / Other related system properties / Signal sensitivity / Tangential sensitivity
caption_attribution_description: This is a video waveform showing a pulse at the tangential sensitivity level
context_page_description: An RF chain is a cascade of electronic components and sub-units which may include amplifiers, filters, mixers, attenuators and detectors. It can take many forms, for example, as a wide-band receiver-detector for electronic warfare applications, as a tunable narrow-band receiver for communications purposes, as a repeater in signal distribution systems, or as an amplifier and up-converters for a transmitter-driver. In this article, the term RF covers the frequency range "Medium Frequencies" up to "Microwave Frequencies", i.e. from 100 kHz to 20 GHz.
  The key electrical parameters for an RF chain are system gain, noise figure and overload level. Other important parameters, related to these properties, are sensitivity; dynamic range and spurious signal levels. In addition, there may be concerns regarding the immunity to incoming interference or, conversely, the amount of undesirable radiation emanating from the chain. The tolerance of a system to mechanical vibration may be important too. Furthermore, the physical properties of the chain, such as size, weight and power consumption may also be important considerations.
context_section_description: Tangential sensitivity, (TSS), defines that input power which results in a video signal to noise ratio of approximately 8 dB from the detector. The thumbnail shows an example of a typical detected pulse at the TSS limit, with the pulse + noise sitting at a level just clear of the noise floor.   The TSS level is too low a value for reliable pulse detection in a practical scenario, but it can be determined with sufficient accuracy in bench tests on a receiver to give a quick guide figure for system performance.
  In a wideband receiver, with a square-law detector, the TSS value at the chain input terminals is given by,
  From this, the S:N of the RF signal, at the input to the detector can be obtained when the video output is at TSS.
  This equation shows that the S:N at RF is typically less than unity, in wideband systems, when the video output is at TSS.   For example, if BR/BV = 500 then the equation gives (S:N)R = 0.17 (≈ -7.7 dB). (Note: a similar result is obtained by using the equation relating RF and video S:N ratios, given in the previous section). 
     The thumbnail shows the simulated video output (at TSS) corresponding to an RF pulse in wideband noise with S:N = 0.17 and a bandwidth ratio of 500.
caption: Tangential Sensitivity
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