:SPRocess:RCOSine:PNOise

Command Syntax

:SPRocessN:RCOSine:PNOise {NONE | PRMS | SPECtrum}

Where N identifies one of up to 64 possible operators {1:64} that can be defined as part of a math function. The operators are numbered in the order that they were originally added to the function.

Query Syntax

:SPRocess:RCOSine:PNOise?

Description

Selects to preserve noise of a Raised Cosine filter operator (:FUNCtion:FOPerator RCOSine). If a status message indicates that the output is questionable due to "The source waveform has not been acquired with enough samples per symbol to accurately represent noise", increase the samples-per-bit setting as explained for the :ACQuire:SPUI:MODE command.

Command arguments:

• NONE. Noise handling is turned off.
• PRMS. Applies preserve RMS noise handling where the noise magnitude is kept the same as the channel.
• SPECtrum. Applies process spectrum noise handling where the function increases or decreases the noise based on whether SIRC is increasing or decreasing bandwidth. The noise power spectrum is assumed to match the channel response.

Turning preserve noise on compensates for the filter function's side effect of reducing a signals noise for adjacent measurement points. Preserving noise causes the operator to quantify the noise on each point on the operator's input waveform and restore this noise on the corresponding data point on the output waveform. Because this increases the fidelity of the waveform, it is recommended that preserve noise be used. An example of an advantage of using this feature is during Mask testing, as without preserving the noise the mask hits counts may be too low (optimistic).

By default, the bandwidth used when preserving the noise is automatically used. To manually set the bandwidth, use the :BANDwidth child command to enter the value and set the :BANDwidth:AUTO child command to OFF.

NONE Argument

The option NONE does not make any special considerations for aliased noise. This is an appropriate choice when the waveform is known to have no aliased components, such as from a real-time or simulated source. This also is the preferred choice when dealing with averaged waveforms where the desired outcome is to remove noise and interference components that are not correlated to the trigger signal.

SPECtrum Argument

The option SPECtrum works by applying the transfer function of the filter to the power spectrum of the noise to determine the appropriate magnitude of the noise on the output signal.

By tracking the accumulated effects of the filtering operations, accurate noise processing can be done even when chaining operations as illustrated in the following figure. In addition to the sampled waveform, information about the acquisition channel and noise power spectrum are maintained in each signal and appropriately processed by each filter. The complete set of auxiliary information is also included when storing FlexDCA waveforms in the *.wfmx file format.

The default behavior of the Process Spectrum noise processing option is to use the noise power spectrum of the input signal. If the input signal is a sampling scope channel with SIRC active, this spectrum will be established by the measured hardware response of the channel. For other channels, the response will be assumed Gaussian with a 3 dB frequency corresponding to the nominal channel bandwidth. This behavior can be overridden by clearing the Track Input Response checkbox and manually entering a bandwidth. If this option is utilized the response will be presumed Gaussian with the selected 3 dB bandwidth.

PRMS Argument

The option PRMS is appropriate when the noise bandwidth is very low relative to the channel and filter bandwidth. It is also appropriate when the aliased components are known to have most of the power within a range of in-band frequencies. This could be from laser RIN, for example, or from intentionally modulated interference/crosstalk. When Preserve RMS is selected, the RMS magnitude of the aliased components will be scaled by the DC gain (the sum of the taps) of the filter. For the low-pass filters (Bessel, Butterworth, Gaussian, Sinc), the DC gain is unity. For the equalizers and embedding/de-embedding operators, the DC gain depends upon the settings of the operator.

Child Commands

• :BANDwidth
• :BANDwidth:AUTo