Chao's Blog

1. ROLL AVG

When a trace is set to ROLL AVG mode, each time measurement is performed the sweep average is taken of the current and past measured data, and the measurement data are updated.

{W_j}(i) = {W_{j - 1}}(i) \cdot (n - 1)/n + W(i) \cdot 1/n

i = 1,2, \cdots ,N.

{W_j}(i): Newly displayed waveform

{W_{j - 1}}(i): Previously displayed waveform

W(i): Newly obtained waveform

N: Number of sampling points

n: Number of averagings

The setting values of the NOISE MASK function are not affected by sweep averaging. The noise mask is executed when the results of the sweep average are displayed.

When CHOP MODE in the measurement sensitivity settings is set to SWITCH, two sweepings is one count.

2. Curve Fitting

Use Trace G

3. OFFSET/SPACING

When set to OFFSET, the difference between the moving marker and each fixed marker is displayed. When set to SPACING, the difference between the moving marker and the smallest numbered fixed marker is displayed along with the difference from each of the fixed markers.

4. Power Spectral Density Markers

Power spectral density markers show power values per normalization bandwidth by assuming the marker position on the waveform to be the center.

5. THRESH, ENVELOPE, RMS, PEAK RMS

Algorithm Description
THRESH Determines spectrum width from the with between points where the waveform crosses the threshold value.
ENVELOPE Determines spectrum width from waveform envelope.
RMS Determines spectrum width from waveform standard deviation.
PEAK RMS Determines spectrum width from waveform mode peak standard deviation.

6. SMSR

SMSR stands for side-mode suppression ratio. SMSR represents the difference between the mode peak and the side-mode level. It is one of the parameters used to evaluate the performance of DFB-LDs and the like.

Fig.1. Side-mode suppression ratio.

7. THRESH LEVEL & MODE DIFF

THRESH LEVEL
This parameter is used to set the threshold level for channel detection.
This setting determines how far down in decibels from the peak level to detect a mode peak as a channel.

MODE DIFF
This parameter sets the minimum value for the peak/bottom difference during channel peak detection.
If the waveform peak/bottom difference equals or exceeds this value, it is detected as a mode peak.

Fig.2. Thresh level and mode diff.