Is a coil FM transmitter frequency affected by my body static?
It isn't that your hand disturbs the magnetic field.

It's that these circuits are sensitive to everything.


Room temperature changes - frequency changes.
You move your hand close - this changes the capacitance between various parts and the frequency changes.
You move the device - you change its relation to various metal objects which changes the inductance of the coil and again the frequency changes.
The battery voltage drops a little - the frequency changes.


These types of circuits work, but will pretty much never be stable unless you make so many changes to them that they aren't the same circuit anymore.

They look simple, and attract people who want to build something easy.  In the end, you spend a lot if time twiddling with a circuit that will never get better.

They demonstrate oscillation and frequency modulation, but they are not circuits you would use for real.

The very function of these circuits is obscure - they depend on poorly defined and unspecified side effects of the components.