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Test Point: TP



TP is used to take measurements from outputs of system diagram blocks.


Name Data Type Description Unit Type Default
ID N Element ID Text TP1
*ZL C Load impedance (set empty for probe) Resistance  
*RBW R Resolution bandwidth Frequency  
*VBW R Video bandwidth Frequency  
*NFFT I Number of FFT bins    
*NAVG I Number of FFT averages    
*WNDTYP E Windowing type   Auto
*WNDPAR R Windowing parameter Scalar 0.0
*WNDWHN E When to window   Auto
*SLDFRC R Fraction of window to slide Scalar 0.5
*SMPSYM R Samples per symbol leave empty to use data stream sample rate Scalar  
*FRQAX E Frequency axis scaling   Auto
*YMIN R Y axis minimum Scalar  
*MASK V Frequency ranges to mask Frequency  
*MSKTYP E Mask type   Pass-Symmetric
*BUFSZ I Maximum buffer size in samples Scalar  
*OVFLTYP E Buffer overflow type if auto the setting from the system diagram options will be used   Auto

* indicates a secondary parameter

Parameter Details

ZL. The load impedance, which can be any complex number in ohms. If left empty, the Test Point functions as a non-invasive probe. See the Recommendations for Use section for more notes on using ZL.

RBW. The default resolution bandwidth for spectrum based measurements. The spectrum-based measurements approximate the number of points for the FFTs from NFFT = SMPFRQ / RBW. Either this or NFFT can control the spectrum frequency resolution.

VBW. The default video bandwidth for spectrum-based measurements. The video bandwidth in a spectrum analyzer is the bandwidth of the video filter, which is a lowpass filter normally used to smooth the spectrum display. Smaller video bandwidths result in a smoother displays. The spectrum-based measurements approximate the effect of the lowpass filter by performing FFT averaging. The number of averages is set from NAVG = RBW / VBW. Either this or NAVG can control spectrum smoothing.

NFFT. The default number of FFT bins to use for spectrum-based measurements. Either this or RBW can control the spectrum frequency resolution.

NAVG. The default number of averages to use for spectrum-based measurements. If set to 0, measurements use cumulative averaging. Either this or VBW can control spectrum smoothing.

WNDTYP. The default type of windowing to perform for the FFT computations used by frequency domain based measurements. When windowing is applied is determined by the WNDWHN parameter.

WNDPAR. The default windowing parameter used for the window type selected by WNDTYP.

WNDWHN. Determines when windowing is applied to FFT computations. When set to Auto, data windowing is only performed when averaging is being performed.

SLDFRC. The default percentage of the time domain data window by which averaged FFTs are overlapped. A value of 1 indicates no overlapping, a value of 0.75 indicates 25% overlap, and a value of 0.5 indicates 50% overlap.

SMPSYM. Use to override the number of samples per symbol of the input signal. The samples per symbol is used by various measurements to determine the number of samples in a data symbol.

FRQAX. Determines whether the frequency axis of the spectrum measurements is displayed in units of absolute frequency or in units of FFT bins. If Auto is selected the frequency axis is displayed in units of absolute frequency.

YMIN. If a value is specified, this value is used as the 'floor' value for the y-axis of the spectrum measurements. All y-axis values that are below this minimum will appear as this minimum value. If the 'DB' option is selected in the measurement dialog then this value is in dB. Leave empty to display the y-axis values as-is.

MASK. Specifies a range of frequencies to be masked in the spectrum measurements. The ranges are specified as pairs of frequencies, one a start frequency and the other an end frequency. These values should be enclosed in '{' '}'. For example, to specify a mask range from 1GHz to 1.1GHz, you would enter '{1, 1.1}' (assuming the project units are set to GHz). The interpretation of the mask is determined by the MSKTYP parameter. Leave empty to not mask any frequencies.

MSKTYP. Determines how the MASK frequency ranges are to be applied. The following choices are available:

  • Pass-Symmetric: Each pair of frequencies in the MASK parameter represent frequency ranges that will NOT be masked out. The frequency ranges are mirrored about the center frequency of the signal.

  • Pass-Absolute: Each pair of frequencies in the MASK parameter represent frequency ranges that will NOT be masked out.

  • Stop-Symmetric: Each pair of frequencies in the MASK parameter represent frequency ranges that will be masked out. The frequency ranges are mirrored about the center frequency of the signal.

  • Stop-Absolute: Each pair of frequencies in the MASK parameter represent frequency ranges that will be masked out.

BUFSZ. Overrides the maximum number of samples that are stored by the test point. If left empty, the maximum is determined from the System Options dialog.

OVFLTYP. Determines what happens after BUFSZ samples have been received at the test point. If set to "Discard Oldest", the first samples received are discarded, while the last samples received are kept. If set to "Discard Newest", the first BUFSZ samples are kept, any new samples received are discarded.

Parameter Restrictions and Recommendations

  1. Many of the parameters only apply to specific measurements and are ignored by other measurements.

  2. The FRQAX, YMIN, MASK, and MSKTYP parameters only apply to the spectrum measurements PSD, PSDN, PWR_SPEC, V_SPEC, and V_SPECN.

Data Input

Node No. Type Purpose
1 Real, Complex, or Digital Monitored Data

Recommendations for Use

When using ZL, blocks connected to the input node will only see ZL if impedance mismatch modeling has been enabled through the System Options dialog box. Measurements, however, always use ZL if it is specified when computing power. See Chapter 2 for details on impedance mismatch modeling.

The parameters such as RBW, VBW, NFFT and NAVG are typically used to establish system diagram-wide settings for these parameters. For example, to set a default RBW of 10 kHz, you could create an equation such as: RBW_Hz=10e3

You can then assign it to the RBW parameter for all TP, VNA, and VSA blocks. Any spectrum-based measurement that refers to one of these blocks uses the RBW setting by default.

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