Frequency modulation means that one frequency is "superimposed" on another frequency, so that two frequencies run simultaneously. The advantages are that you can use two frequencies at the same time and that the frequencies can penetrate deeper into the tissue.
Let's take the radio as an example: The carrier wave of is 98 MegaHz i.e. This frequency is modulated by the voice of the speaker or the music (about 50-20,000 Hz). The faster carrier wave is deformed by the slower wave.
A distinction is made between frequency modulation (FM) and amplitude modulation (AM). With FM the carrier wave is deformed horizontally, with AM vertically. Frequency therapy with the Rife machine Diamond Shield uses AM. The fast Clark frequencies (200-800 kHz) are vertically deformed by the 128 times slower modulation frequency (see red curve).
Hulda Clark has set her zapper frequency as a positive offset. This means that the square wave does not change between minus and plus (as with alternating current, for example), but remains in plus. There it oscillates between zero and the maximum voltage. The square wave switches the device continuously on and off.
In addition, Dr Clark recommended a residual voltage - a kind of safety distance between the lower frequency line and zero. You can see it on the graphic of the oscilloscope.
In the Rife machine Diamond Shield this is realized as follows:
The carrier wave has a positive offset without residual voltage, so it switches on and off and overcomes the skin resistance. The skin consists of several layers which are charged alternately PLUS and MINUS. The skin effect is avoided by the positive offset of the carrier wave. The modulated shaft has a positive offset with residual voltage.
It makes sense to set the carrier wave and the modulated wave in a ratio of 2 high x, i.e. 2, 4, 8, 16, ... Thus the two waves are "related" to each other, so to speak. The Diamond Shield Zapper has Dr Hulda Clark's frequencies modulated with the factor 128.