How to use a spectrum analyzer preamplifier and signal generator to measure the noise figure

Many noise figure measurements can be made using only a spectrum analyzer and a preamplifier. Spectrum analyzers, preamplifiers, and signal generators are all that is needed to cover the frequency of the device under test. The accuracy of this method is lower than that of y-factor techniques that require calibration of noise sources, and comparable to the amplitude accuracy of the analyzer for the frequency of interest.

The specific measurement steps are as follows:1The signal generator and spectrum analyzer are set to the frequency of the measured noise figure to measure the gain of the device.

Label the value as gain(d). 2.The same method is used to measure the preamplifier gain.

Label the value as gain(p). 3.Disconnect any input from the spectrum analyzer and set the input attenuator to 0dB.

The preamp input does not have any connections. Connect its output to the spectrum analyzer input. When you make this connection, you will see an increase in the average noise level displayed by the analyzer.

4.Connect the input of the device under test to its characteristic impedance and the output to the preamplifier input. At this point, the noise level displayed by the analyzer should increase.

5.Set the Spectrum Analyzer** bandwidth (VBW) to 1% or less of the resolution bandwidth. Press the Marker Function (MKR FCTN) key, and then press the Noise Marker On soft key.

Place the marker on the frequency of the noise figure to be measured. Read the marked noise power density reading in dBm Hz and label it as noise(o). 6.

The noise figure NFIG of the device under test is then calculated: NFIG = noise(o) -gain(d) -gain(p) +174 dBm Hz

It looks like a good look.

The need for a logarithmic amplifier in a spectrum analyzer: a preamplifier is used to amplify the amplitude of the signal being measured, which is used to extend the dynamic range and improve the sensitivity of the test. The signal tracking source is a swept signal output generator (which can be fixed) that measures the frequency characteristic curve of the device under test.

Spectrum analyzer is an instrument for studying the spectral structure of electrical signals, which is used for the measurement of signal parameters such as signal distortion, modulation chain reed, spectrum purity, frequency stability and intermodulation distortion, and can be used to measure some parameters of circuit systems such as amplifiers and filters, and is a multi-purpose electronic measuring instrument.

Traditional products. The front-end circuit of the traditional spectrum analyzer is a tunable receiver within a certain bandwidth, the input signal is converted by the frequency converter and output by the low-pass filter, the filter output is used as the vertical component, the frequency is used as the horizontal component, and the coordinate diagram is drawn on the oscilloscope screen, which is the spectrogram of the input signal. Since the frequency converter can reach a wide frequency range, such as 30Hz-30GHz, and can be extended to more than 100GHz in conjunction with the Shed Search External Mixer, the spectrum analyzer is one of the measurement instruments with the widest frequency coverage.