High sensitivity is a critical factor for any type of receiver; the front end of the receiver mostly affects the sensitivity. This includes the antenna (must have high gain), filter (must have low loss), and amplifier (must have low noise figure). Any type of loss, either passive (such as filter or attenuator) or active (such as limiter), contributes directly with a 1:1 ratio or more added to the noise figure. Noise Power is the noise level measured at the output of a receiver or amplifier for a specific bandwidth which is often called 1/f noise or white noise.

Determining the Noise Power (Pn) of a Receiver

For example, what is the noise power of an amplifier with the following parameters? And what is the output signal to noise ratio with an input signal of -80 dBm?

What is the noise power and signal to noise ratio of the amplifier above if adding a 20 MHz filter at the output?

Often measuring equipment provides incorrect readings of the noise power measurement for the unit under test (UUT) because the test equipment has limited bandwidth; this includes power meter spectrum analyzers and network analyzers. Therefore, the bandwidth of the test equipment must be taken into account during measurement of the unit's noise power. The true noise power of the UUT can be calculated by using the equation above by knowing the measured noise power and the bandwidth of the test equipment.

- M. G. (Aug 1999)