Yutaka,
1st of all, the IEC2-6gal.bin IEC wave command file has a sample rate of 200 Hz NOT 250 Hz.  There does seem to be a problem w/ this cuz of the error msgs.  The command waveform needs to be resampled at 250 Hz if this is the problem.  It actually may run better at 200 Hz.  The 469D s/w upgrade checks this more closely so that could now be the problem.  Also, I do NOT like the ASD for the command waveform.  If the plots you sent to me are the ASD for the IEC wave then I KNOW THERE IS SOMETHING WRONG.  The desired ASD plot is NOT RIGHT.  The quiet section from about 15 Hz to 45 Hz is VERY DISTURBING.  I have included MATLAB PSD for IEC2-6gal.bin.  You can see it has a lot more data out to 10 Hz than what is shown on the STEX plot.  The response may not be that far off.  The analysis I did was for 1024 lines.  I found that fewer lines gives erroneous data cuz there is content between the few lines that is bigger.

So, I think there is definitely a sample rate problem and there may be a desired PSD amplitude problem.  Brad did not come in today; I will call him at home tonight.  Jim Langseth in in Taiwan right now; I will contact him by e-mail today as well.  Make sure that sample rates are ok 1st and that may solve all problems.  Even running at 200 Hz is not so bad for aliasing, just NOT 50 or 100 Hz.
Rod Larson
