Reactance
and
Resonance
What is Reactance?
• The resistance to AC current flow caused by
capacitance or inductance.
• Measured in ohms
• Symbol used is X
What is Inductance?
• The resistance to AC current flow caused by
resistance, reactance or any combination of the
two
• Measured in ohms
• Symbol used is Z
What is Capacitive Reactance?
When a circuit containing a capacitor is first energized, the voltage across the
capacitor is zero but the current is high. As time passes, the voltage
increases, current goes to zero.
Capacitive Reactance
As the frequency of the applied signal increases,
capacitive reactance decreases
As the frequency of the applied signal decreases,
capacitive reactance increases
What is Inductive Reactance?
When a circuit containing a inductor is first energized, the current across the
inductor is zero but the voltage is high. As time passes, the current
increases, voltage goes to zero.
Inductive Reactance
As the frequency of the applied signal increases,
inductive reactance increases
As the frequency of the applied signal decreases,
inductive reactance decreases
Resonance
Maximum power transfer occurs
when the source and load impedances
are equal.
Demonstration:
Use LC tuner to
match source to
load impedance.
Resonance
Most transmitter have a 50 ohm characteristic
impedance. The use of a transmatch will match the load
to the source impedance. Pi & T networks.
Impedance Matching
Caution:
Using an impedance
transformer at high power
can result in core
saturation, creating
harmonics and causing
signal distortion.
RF impedance transformers are often used to equalize
impedances of source and load to maximize the transfer
of power. Source = Load