Well,the OP mentioned "inverters" and MY post questioned why an inverter was used when the generator already makes a sine wave output. Then someone else mentioned Honda,and I researched that to answer my own question.
generating a sine wave from a DC supply requires switching large currents.the switchuing generates harmonics.
Now,the sine wave output may be very clean and right on freq,but the inverter's switching circuitry may radiate those harmonics,that could be picked up by other instruments. It takes very careful design to minimize radiated noise.
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