I made a script (/users/aaron/40m/GPIB/tds_dump.py) that grabs data from a Tektronix scope and packages into a pickled dict with the following structure:

1. ch1
   1. times ("ts")
   2. values ("vals")
   3. channel info ("info")
2. ch2
   1. ""
3. etc

I made a python notebook that does the following:

1. Grab the data from the pickle above
2. Fit a triangle wave to the drive signal
3. Determine the (change in Volts) / second from the triangle wave, as well as define the times of a single sweep of the PDH error signal
4. Trim the error signal data to contain the PDH signal from the carrier and two sidebands only (the original trace was for three periods).
5. Fit the functional form of the PDH signal to the trimmed error signal. 
   1. The sideband frequency is fixed at 35.5 MHz, and the scaling of Volts-to-Hz is left free, so this fit gives the calibration of IF volts to Hz.
6. Grab the spectra (already saved from the Agilent with the netgpib scripts) and apply this V-to-Hz scaling
7. Plot the spectra

The fit in step (5) is still looking quite bad, despite the fitted values being close to the expected. Since we really just want a calibrated spectrum, I'll instead fit a line to the linear portion of the PDH error signal for the carrier and both sidebands, then determine the scaling from that.