HP 3585B Spectrum Analyzer
I've written a program to capture screen images from an HP 3585B spectrum analyzer (an 80s vintage beast that covers from 20Hz to 40MHz). I also wrote a simple control program that allows you to set most of the 3585B's parameters such as center frequency, span, resolution bandwidth, and reference level. These programs run under the Linux operating system using the LinuxGpib driver and interface library, and the perl programming language.
The screen capture software generates a PNG format graphics file that more or less matches what you see on the screen, with a few extra features. The most important addition is the ability to create a trace that is the average of a number of sweeps; this makes up for the lack of a "video average" mode in the analyzer. In addition, you can display the minimum and maximum values as well as the average. Scroll down this page to see some examples of these functions in action.
Finally, you can choose multiple colors for the trace, and force the output image to be transparent. Used together, those features mean that you can use Photoshop or the Gimp to "stack" several traces into a single image. I don't currently have an example of that feature used with the 3585B, but here is a stacked trace taken from an HP8569B analyzer with similar software.
These programs are available at febo.com/pages/n8ur_programs. I'm not putting precise links here because the filenames are likely to change for a while yet. You will need to download the "n8ur.pm" and "hp3585b.pm" modules as well as the main program files.
Note: this software will not work with the "A" model of the HP3585; its GPIB commands are very different from those in the "B" version.
Here are some examples of output from the screen capture program.