How does noise marking work on a spectrum analyzer?

1 The near-Gaussian shape of the resolution bandwidth (RBW) filter is corrected to a rectangular equivalent noise bandwidth (NBW) that transmits the same noise power. The correction factor ranges from 3 dB bandwidth in the case of a filter of > or = 1 kHz. 2 Poor db response (under-response) is caused by errors in the average of logarithms of data points and the display interval of noisy signals.

The ESA and PSA series can be accessed by pressing the marker> More > function > Marker Noise (ESA)) or the Marker FCTN > Marker Noise (PSA)) to access the Marker or the Noise Marking function in the Marking function menu. When the noise marker is activated, if the detector is set to auto (the default), average detection is activated. The average type is set to Power (RMS)4, and the above equation calculates the total power over the frequency interval.

Correction of the RBW filter forming factor is applied and the result is normalized to a 1 Hz bandwidth and displayed as dBX (1 Hz), where X depends on the amplitude unit selected, as in dBm (1 Hz)3 Average detector types were not available in earlier analyzers. The detector averages all digitized data in the frequency segment according to the selected average type. see note 4.

In ESA, if the RBW < 1 kHz, a sample test is used. 4 Since the average power (rms) is the square root of the sum of the squares of the voltage data (derived from the inside of the segment divided by the zin in the analyzer), it calculates the true average power. However, if the user chooses the logarithmic power (**) average, the db under-response error can be compensated.

In PSA, the user can also choose the average voltage, in which case the under-response of the DB can be compensated.

The noise labeling algorithm works very similarly to the , ESA, and PSA series spectrum analyzers. The biggest difference is the type of assay used. All of these analyzers use the following equation to calculate the labeled noise power:

This value is equal to the sum of the left endpoint x1 plus the right endpoint x2 ( *Total length of spacing, where the endpoint is in the center of the noise marker). The px value is the power ratio of the value of the indicated trace data at point x to the reference value, for example, if x = -60 dB, its value is. Span Freqpts - 1 is the spacing of the trace data points.

NBW is defined in Note 1 below. The 8590 and 8560 Series can access the Noise Marking function in the Marking Function or the Marking Menu by pressing the MKR FCTN > MK Noise ON (859XE) or MKR > MKR Noise ON (856XE EC). When the noise marker is activated, the sample detection is activated, the equation is used to calculate the total power in the frequency interval, the correction to support the RBW filter forming factor is applied1, the correction of the average error is applied2, and the result is normalized to a 1 Hz bandwidth and displayed as dbx (1 Hz), where x depends on the amplitude unit selected, as in dBm (1 Hz) To get accurate measurements, make sure that the noise marker is installed so that all data points are above the noise floor.

The data points occupy almost 5% of a horizontal grid section or spacing on the 859xe, in which there are a fixed 401 display points; At the same time, half of the 856xe has a fixed 601 points.

How to use a spectrum analyzer.

Measuring signal-to-noise ratio? The first thing to know is the frequency range of the signal and noise being tested, as well as how much signal strength there is. The structure of a spectrum analyzer is somewhat similar to that of a superheterodyne receiver, and its working principle is to apply the input signal directly to the mixer through the attenuator.

The variable local oscillator generates an oscillation frequency that changes linearly with time through a scan generator synchronized with the CR, and then the intermediate frequency signal (IF) is mixed with the input signal by the mixer

The amplification, filtering, and detection are transmitted to the vertical orientation board of the CRT, so that the signal frequency and amplitude are displayed on the vertical axis of the CRT.

correspondence. Filter.

Bandwidth often affects signal response, so the filter is characterized as a Gaussian filter.

To put it simply, RBW is the lowest bandwidth difference that can be clearly distinguished between two signals of different frequencies, and the bandwidth of two signals of different frequencies is lower than that of the spectrum analyzer.

RBW, at which point the two signals will overlap and be difficult to distinguish. If you use a lower RBW, it is helpful to analyze signals of different frequencies, but a lower RBW will filter out some of the higher frequency signals, resulting in signal display.

Distortion is generated, and this distortion value is closely related to the set RBW. Although a higher RBW is helpful for the analysis and detection of wideband signals, it will increase the noise floor and reduce the sensitivity of the test.

Detecting low-intensity signals can be an obstacle, so choosing the right RBW width is important for proper use of a spectrum analyzer. Another important parameter is the bandwidth VBW represents the single signal required to be displayed on the screen.

Minimum bandwidth. As mentioned earlier, when measuring the signal, the first bandwidth needs to be selected appropriately, and if it is not selected properly, it will cause difficulties in detection. So how to adjust it must be studied. The bandwidth of the RBW must be greater than or equal to.

VBW: When the RBW is adjusted and the signal amplitude does not change significantly, the RBW is the bandwidth that can be used. The filter will not be able to fully charge the signal. Therefore, the larger the RBW, the faster the scanning time, and vice versa, so choose the appropriate width of the RBW

It's very important. Therefore, generally speaking, a wide RBW can fully reflect the waveform and amplitude of the input signal, and a lower RBW can distinguish signals of different frequencies.

The characteristics of the noise spectrum analyzer are:

1. Built-in octave filter (switching capacitor);

2. The use of digital detection technology greatly improves the stability;

3. Small size, light weight, easy to use;

4. It can measure instantaneous A sound level or sound pressure level, automatically sample and calculate the center frequency of the octave filter according to the preset measurement method and octave filter, and automatically print out the spectrogram and data at the end of the measurement;

5. Through the RS-232 interface, the host and the microcomputer can communicate, and the data can be further processed, analyzed and output;

6. The measurement results can be stored in the instrument for a long time.