= Impedance =

Ac voltage and current are often in phase, in something such as a resistor.
However, they can become out of phase when passing through a [[Capacitor]] or
[[Inductor]]. Capacitors are resistant to changes in voltage, causing voltage
and current to get out of sync. Inductors are resistant to chagnes in current,
causing voltage to get out of sync.

This getting out of sync is called reactance. The total reactance is called
Impedance. Impedance is measured in Ohms, shown as Z

== Inductors ==

An inductor creates a magnetic field, which when the direction of the voltage
switches, the field resists this change, creating a phase shift. This causes
some resistance, which is why impedance is measured in Ohms. The phase shift,
and therefore the resistance, is directly based on the frequency of the AC
signal. The relationship is shown below

X,,l,, = 2(pi)fL

Where X,,l,, is the inductive reactance (in Ohms),
f is AC signal frequency (in hz),
and L is the inductance (in henery)

NOTE as the frequency increases, the inductive reactance increases

*Inductors always make voltage lead current*

== Capacitors ==

A capacitor creates an electrostatic field, which swaps which plate of the
capacitor each charge forms on, when the direction changes. As a result, this
creates some resistance, measured in Ohms. The phase shift (in current) is
based on the frequency of the AC signal. The relationship is shown below

X,,c,, = 1 / 2(pi)fC

Where X,,c,, is the capactive reactance (in Ohms),
f is the AC signal frequency (in hz),
and C is the capacitance (in f)

NOTE as the frequency increases, the capacitive reactance decreases

== Impedance matching ==

Internal impedance of a source limits its ablity to deliver power. A D cell for
example has a lower impedance than a hearing aid battery, so despite both
creating a voltage of 1.5V, the D-cell is able to deliver more current.

When the impedance is matched between two devices the power delivery is more
efficent. Most ametuer equipment has an impedance of 50ohms, including antenna
feed points, coax, and transceivers. When this impedance does not match,
[[SWR]] is formed and can cause damage to the transceiver.

To match the impedance of two circuits, LC circuits are used to match the
impedance. Two types are the pi and T network circuits, named such due to their
appearance.

Impedance matching can also be performed by transformers. Impedance
transformers do this exact task.