parazapper
The secret to the square wave is that it is actually made up of a large number of sine waves.
If the base frequency is 2500 Hz, then:
3rd harmonic = 7500 Hz sine wave
5th harmonic = 12500 Hz sine wave
7th harmonic = 17500 Hz sine wave
and so forth all the way up to 1,000,000 Hz ( 997,500 Hz ) or higher in better models.