# Antenna VS Coil

So I sorta understand that antennas are just wires connected to a signal out with no reference to ground. (That's for a different question)

How does a coil/inductor with one side attached to v+, one to v- (aka gnd) differ from an antenna attached just to v+? Wouldn't a coil work better since more current flows through the wire? How does any current flow through an antenna?

I know that a magnetic field can be formed in a solenoid, can a magnet be formed with an antenna?

This is a mechanical simplification.

Imagine you are holding a stick of 1 metre in length and the stick is made from a flexible material such as er... rubber or even thin metal. If you moved the stick with your hand slowly, it would barely flex at all - your hand movement would be almost perfectly matched by the movement at the end of the stick and no force is transmitted down the length of the stick.

The above describes an antenna/wire where the frequency from the transmitter is much too small.

Now consider the situation where you could "shake" (or oscillate) that stick really rapidly - your hand would be moving rather quickly from point A to point B then back to point A (and repeating) but the end of the stick would be virtually at standstill.

The above describes the scenario where the transmitter frequency is too high. (The experts amongst us will of course point out that multi-mode oscillations may occur but for now bear with this simplification).

And now, the goldilocks frequency. At the right frequency you can cause the end of the stick to massively move with hardly any movement of the hand - the only constraint is that the hand movement should pretty much precisely match the frequency that sustains the basic mechanical oscillation.

This is what happens with an antenna - for the stick at mechancial resonance (see also cantilever for the maths) significant forces are being transmitted via the hand despite the movement being quite small and, the end of the stick is attaining significant movement. Relate in your mind the forces to current flow and the movement to voltage and you have an antenna.

What makes this happen in the stick is the energy input from your hand, mass and springiness. What makes this happen in an antenna wire is energy input (the transmitter feed) capacitance and inductance.

So the "resonant stick" takes from the hand a significant force with very little movement - this is like the 50ohm antenna input on the antenna - it's quite low impedance and, on the end of the stick there is movement amplification but the force at the end is small - it comverts an impedance and, for an antenna hopefully matches it to the impedance of free space (377 ohms).

I hope this helps.

The nushell version is that an antenna IS a complete circuit in itself even though it appers to be "just a wire". It has its own inductance (in the wire) but also "invisible" capacitance connecting its ends. The two components (inductance and capacitance) form a resonant circuit, and indeed the whole point of antenna design is to select a shape (even if just the lenght of a wire) that maximizes the current at the desired frequency. If that sounds too abstract, you could look at a more detailed/animated explanation; the bouncing back and forth of the electrons in the antenna/wire in that video are the resonant waves.

As for connecting the ends of an antenna to a DC source in order to increase the current through it: that won't help with the intended application of an antenna, because you'll increase current at a useless (DC = 0Hz) frequency and that will just generate heat for no benefit in this application; on the other hand if you want to create a space heater... then it is a good idea.