Radio receiver sensitivity defines the weakest signals that can be successfully received

Radio receiver sensitivity defines the weakest signals that can be successfully received. Whether it is the reception of analog radio signals with audio modulation, whose listening quality gradually deteriorates as the signal merges into noise, or digital data signals where the bit error rate increases and throughput decreases — signal-to-noise ratio is important in any radio frequency circuit design.

Receiver sensitivity is a key operational parameter for any communication system and is limited by the system's own noise.

Radio receiver sensitivity includes:
Signal-to-noise ratio
SINAD noise factor
Minimum noise level NF
Intermodulation

Thus, receiver sensitivity is a critical parameter affecting the performance of any communication, broadcasting, or other radio system.

In fact, two main requirements for any radio receiver are its ability to separate one station from another, i.e. selectivity, and sensitivity, so that signals can be amplified above noise sufficiently to be demodulated. Therefore, receiver designers work with many parameters to ensure these and many other requirements are met.

Methods of Determining Radio Receiver Sensitivity

Since the radio frequency sensitivity characteristic of any receiver is of paramount importance, it must be quantitatively specified. Several methods and metrics are used depending on the intended application:

Signal-to-Noise Ratio (SNR)

Signal-to-noise ratio is a direct comparison of a given signal level to system noise and is a useful measure of receiver sensitivity. It is commonly used for shortwave radio stations. Typically, sensitivity specifications are given as the input voltage that produces a 10 dB SNR, although sometimes 15 dB or other values are used.

SINAD

SINAD is a somewhat more formal measurement of receiver sensitivity than simple SNR. It also includes distortion and noise levels in the detected signal.

SINAD is often used with VHF FM receivers and portable radios used for line-of-sight communication. The SINAD method is widely applied to FM stations in VHF / UHF communication devices, but it can also be used for AM and SSB.

Noise Figure

Noise figure is a parameter of the radio frequency receiver obtained by comparing noise added by the device (such as an amplifier or other system component) to the total noise level at the receiver input. Noise figure is usually expressed in decibels and abbreviated as NF. The NF of a device or system is a logarithmic form of the noise factor. It is widely used to define sensitivity and noise characteristics of receivers, system components, or entire systems.

Carrier-to-Noise Ratio (CNR)

Carrier-to-noise ratio (CNR) is the signal-to-noise ratio (SNR) of the modulated signal. This term is less widely used than SNR but can be applied when distinguishing characteristics relating to the RF bandwidth signal and the baseband analog message signal after demodulation are necessary.

Minimum Discernible Signal (MDS)

The minimum discernible signal is the lowest signal level that a radio receiver can detect, i.e. one that can be processed by its analog or digital signal chain and demodulated to provide useful output information.

Error Vector Magnitude (EVM)

Error Vector Magnitude, EVM, is a measure used to quantitatively evaluate the performance of digital radio transmitters or receivers. By plotting the positions of in-phase and quadrature components of the signal, a so-called constellation diagram is created.

On the constellation diagram, different points correspond to various digital states. Ideally, a transmitter should generate digital data points as close as possible to these positions — the channel should not degrade the signal so that the received data points deviate from them, and the receiver should also preserve these positions.

In practice, noise is present in the system, and the received data points do not exactly coincide with these ideal locations. The error vector magnitude quantifies how far the actual received data deviates from the ideal. EVM is also known as received constellation error (RCE). It is widely used in modern data transmission including Wi-Fi, cellular networks, and IoT systems.

Bit Error Rate (BER)

Bit error rate is a measurement commonly used for digital systems. As signal levels decrease or communication quality degrades, the number of bit errors increases. Measuring BER provides insight into the signal-to-noise ratio in a format more useful for digital applications.

In all receiver sensitivity specification methods, it is recognized that the limiting factor is not the available gain level but the levels of noise present, whether generated inside the receiver or external.