Q: What is the difference between receiver sensitivity and receiver selectivity?

Sensitivity is an indication of how weak a signal the receiver can still resolve into a useable output. On a datasheet, a figure is given for receiver sensitivity. The value is most usually given in units of dBm. Some examples might be -108dBm, -112dBm, -120dBm. The lower the number the more sensitive the receiver is. Remembering that with negative numbers, -120dBm is lower than -108dBm, the receiver that has a sensitivity figure of -120dBm is more sensitive than a receiver with stated sensitivity of -108dBm.

Receiver selectivity is an indication of the receiver’s ability to ignore strong signals on adjacent radio channels to the tuned frequency. A well-designed receiver will be able to correctly resolve weak signals on the wanted channel even if there are stronger signals on the next channel up and/or down. Receiver selectivity is primarily determined by the quality of components used in the receiver’s intermediate frequency circuit stages. Like most things in life, more expensive components produce better results. At Wood & Douglas our focus is on producing radios with optimum performance rather than designing with component cost as top priority. That is why we are the first choice for those looking for professional radio solutions that will be used in challenging RF environments.

Receiver selectivity is given in units of dB. A typical value for a W&D receiver designed for 25kHz radio channel bandwidth is 70dB. That means that when receiving a weak signal on the wanted frequency, it would take a signal 60dB stronger (x1,000,000) stronger on an adjacent channel to cause receiving difficulties. The larger the number the more selective the receiver circuitry is: e.g. 70dBm is better than 60dBm.

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