No, a variable capacitor cannot directly substitute a crystal oscillator for frequency modulation (FM) of electric current to modulate radio waves.
A crystal oscillator is a highly stable electronic circuit that generates a precise and stable frequency signal based on the characteristics of a crystal. It is commonly used in FM transmitters to provide a stable carrier frequency for modulation.
On the other hand, a variable capacitor is typically used for tuning or adjusting the resonant frequency of a circuit. It can be found in radio receivers or other tuning applications where the frequency needs to be varied within a certain range.
While a variable capacitor can help adjust the resonant frequency of a circuit, it does not provide the necessary stability and accuracy required for FM modulation. FM modulation involves precise and consistent changes in frequency, and a crystal oscillator is designed specifically to provide the stability and accuracy required for this purpose.
If you want to perform FM modulation of electric current to create radio waves, it is recommended to use a dedicated FM modulation circuit that includes a stable carrier frequency source such as a crystal oscillator.