He knew that in synchronous generator, if the magnetic flux of the field system is distributed perfectly sinusoidal around the air gap, then e.m.f generated in each full-pitched armature coil will be sinusoidal completely.
He had an old and small 50HZ generator. He decided to use it for 100HZ signal producing.
For this purpose, he changed standard distributed windings of armature that located in stator slots. Also he connected one electronically mid-pass filter which tuned with 100HZ frequency in generator output.
The output voltage of generator was not sinusoidal and it is distorted by new space flux distortion. He had a lot of harmonics in output stage of generator, but he never observed 100HZ signal in filter output.
He more and more tried and changed the stator winding distribution frequently, but he couldn't to produce purposed signal.
Why? Why couldn't he?