Need to generate 5% modulation, 20 Hz on 115 VAC signal to test this unit. What do I use?
If all you need to do is modulate a 115V 20hz signal, an old Elgar SW (smartwave) series AC power source has an external modulation input.
See page 9 of this link - http://www.programmablepower.com/ac-power-source/CSW/downloads/AMETEK's_Elgar_SW_and_California_Instruments_CSW_Form_Fit_and_Features_Comparison_Tech_Note_10_6_11.pdf
If you need 5% modulation at 20hz riding on a 115v/60hz wave you need two of these (or similar power sources) phase locked together.
Signal needs to be 115VAC/400Hz modulated with a 20 Hz signal to 5% AM Modulation.
An Agilent 33250A Function / Arbitrary Waveform Generator and a Fluke 5205A Precision Power Amplifier works great. The 33250A with an Elgar AC Power Source as an amplifier also works well but the 33250A may not have enough output voltage in AM mode to fully drive the AC Power Source to 115V so I also use an ST series transformer to step up the output from the 33250A to the input of the AC Power Source. I monitor the modulation, AM or FM, as required at the output of the 33250A even though the 33250A is always very nearly spot on. I monitor the 115V output from the AC Power Source with a 34401A, I have had some issues using a 3458A with modulated AC but it can be done.