How can I transfer trace data from the 89400 VSA to my PC?

Operational "How to" Guides

Summary

Description

The VSA always saves data in SDF, standard data format. A manual called
Standard Data Format Utilities ships with your VSA. In the back is a plastic sleeve that contains PC floppy disks with the conversion utilities for SDF. The most frequently used utility is called "sdftoasc" and is explained on page 4-39 of the manual. The manual is not on line, but may be purchased using PN 5061-8056, which includes the disks.

The utility is run from the DOS prompt. You must specify the source file, e.g. mydata.dat, and a destination file, e.g. mydata.txt. Here is an example of a complete line in its simplest form that is executed from the directory containing the source file and the utility:

C:\>SDFTOASC rampup.dat rampup.txt

This line produces two columns of 512 complex points (voltages) if the default 401 frequency points is selected on the VSA. The first column is real data and the second is imaginary.

There are several optional switches that may be used such as /X to add a frequency column. These are all explained with examples in the manual. After conversion if desired, use the viewdata.exe utility to see the ASCII data for a confidence check. Then simply open the new file in any ASCII application like Word or Excel.

The same utility is used for time capture files where the /S switch denotes the number of time records within the time capture to convert. (A time capture is a series of successive time records with no gaps in time between them.) For example:

C:\>SDFTOASC offair.cap offair.txt /S:0-2 /X

produces one column of X-axis data (time, not frequency) and two columns of real and imaginary data (voltages) for the first 3 time records in the capture file, or 3*512 complex points total (1536 rows in Excel). The example uses a .cap extension to differentiate time capture data from normal acquisition data, but a .dat extension may also be used.

For a time capture in Ch1+jCh2 mode, the data is always all real since this mode is in baseband time (the IQ detector is off). If you use the "/S:" switch without a range to convert only the first time record (default), the result is one column of 1024 real values of I data which correspond to the first and second time records from channel 1. (This assumes again that the default 401 frequency points are used in the setup.)

Here is where it gets a little tricky. The utility correctly reports 1024 time points since 401 frequency points equals 1024 time points in baseband time (401 * 2.56). However, VSA signal processing interprets each time record as zoom time regardless of the mode, and limits the number of time points per record to 512. So the utility is actually converting 512 points from the first record and 512 points from the second record of channel 1, or I data only, to provide a total of 1024 points.

In order to get both I and Q data, use the /R switch too. Here is an example:

C:\>SDFTOASC ch1jch2.cap ch1jch2.txt /S: /R:0-1,C /B:,

This produces two columns of complex data in Excel, the first for I data (channel 1) and the second for Q data (channel 2), for the first 2 time records in the capture file for a total of 1024 points.

So an idiosyncrasy of the utility is that it will always produce double the number of time records requested when the VSA is in Ch1+jCh2 mode.