Test and Measurement RF Equipments Section

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Noise Figure Meter | A Meter used to measure Noise Figure

This page covers Noise Figure Meter basics. It mentions block diagram of Noise Figure Meter. It mentions Vendors or manufacturers of Noise Figure Meter.

Noise Temperature: All the passive electronic components generate some noise due to random motion of charge carriers flowing in it. The greater the temperature, the greater is the motion of carriers. This results into greater noise power generated by the component. The noise power can be expressed as follows:
P = K T B
Where, K = 1.38 x 10-23 Boltzmann constant
B = Bandwidth
T = Temperature in Kelvins

Noise Figure: A perfect amplifier will not add any noise to incoming signals, but practically it adds some noise. This can be equivalent to temperature of resistor at which it produces same amount of noise. This is known as excess noise temperature. The lower the excess noise temperature, good is the amplifier. The amplifier can be characterized with noise figure term. The noise figure is the ratioof excess noise temperature to room temperature.
NF = (Te + Tr)/Tr
Ideal amplifier should have Te = 0 or NF = 1 or 0 dB.

There are various methods of noise figure measurement viz. Using noise sources, Y-factor method, Signal generator twice power method, direct noise measurement method etc.

Noise Figure Meter

The figure-1 depicts noise figure meter measuring noise figure of a DUT (i.e. Amplifier or converter under test). First Noise source is calibrated along with noise figure meter. Later DUT is inserted between output of noise source and noise figure meter input which reads out noise added by the DUT. This method is popular and reliable.

The down converter is added at the output of amplifier if its frequency range is not within the range measured by noise figure meter. Moreover external pre-amplifier is added, if output of DUT is not sufficient enough to conduct the measurement.

Noise Figure Meter Vendors or Manufacturers

Following table mentions Noise Figure Meter Vendors or Manufacturers.

Vendor or manufacturer Description
Keysight Technologies Model: N8975A , Frequency: 10 MHz to 26.5 GHz
Ailtech Automatic Noise Figure Indicator, Model: 7514
Bruel & Kjaer 4427 Noise level analyzer
Ducommun Noise figure and gain test set

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