Avionics News October 2019 - 69

Figure 2

producing voltage, which is out of synchronization with
the voltage applied. We call this capacitive reactance
(XC). When all factors are accounted for (inductive
reactance (XL), capacitive reactance (XC), and resistance),
we have impedance (Z). We will save impedance in
circuits with both XL and XC for another month.
XC differs from resistance in that the reactance
changes with frequency. Reactance is inversely
proportional to frequency. Put simply, as frequency
increases, reactance decreases (the opposite of XL).
Capacitive reactance can be calculated by using the
formula: XC=1/2πFL. F is the frequency, and C is the
inductance in farads. The answer will be in ohms. For
example, let's use a 2 µF capacitor in a circuit using
10 kHz. 2 x 3.14 = 6.28. For the next step, we have
10,000 Hz, times 0.000002 F. 1,000 x 0.000002 = .02.
To finish, 6.28 x .02 = 0.1256. Don't forget to take the
reciprocal of this answer 1/0.1256 = 7.96 Ω.
Let's increase the frequency to 40 kHz: 2 x 3.14 x
40,000 x 0.000002 = 0.5024. 1/0.5024 = 1.99 Ω. When
we quadruple the frequency, we reduce the impedance
to one-fourth of the original value. This relationship
makes capacitors useful for filters, which is a subject
we can deal with during another month.
Like inductors, things get more complicated when
resistance is factored into the circuit. Remember, a
perfect, zero-resistance wire is only possible in theory.
In reality, there will be some resistance in any circuit
built. Engineers will design circuits with both resistors
and capacitors, and the resistance will have an effect on
the phase relationships within the circuit.
To calculate the phase relationships in a resistive
and capacitive circuit, we use phasor diagrams similar
to those used in RL circuits. The difference is in the
direction of the arrows. Inductance is shown with an
arrow toward the top of the page, and capacitance
is shown with an arrow drawn toward the bottom
of the page. When we discuss circuits with all three
components, we use arrows in all three directions. As
with the inductive circuits, we use trigonometry. To

visualize the phase relationships, we can
use a diagram. To keep this short, we will
focus on the diagram with a minimum of
trigonometry. Detail on the trigonometric
analysis can be found in any electronics
textbook.
Figure 3 shows the phasor diagram
along with a math example to solve for Z.
Capacitive reactance is vectored downward,
and resistance is vectored to the right. With
the red lines added, we have a box. The Z
vector is drawn from corner to corner, thus
forming two right triangles. In this case, XL is equal to
R. We can see (or, you can use Pythagorean's theorem)
that the phase angle (Ф) between current and voltage is
45 degrees. More resistance will reduce the phase angle,
and less resistance will increase the phase angle.
The total impedance of the circuit is represented by
the Z vector and can be calculated using Pythagorean's
theorem. Visually, we can see that Z is a greater value
than the individual R or XC, but less than the sum of R
or XC. For an easy example, we can use 10 Ω for both
R and XC as shown in Figure 3. The answer of 14.14 Ω
fits the rule where the Z is greater than the individual
reactance or resistance but is less than the sum of both.
The capacitor will not dissipate any power; however,
thanks to counter EMF, there is a voltage drop. The rule
for determining true and apparent power applies to a
capacitive circuit as it does with an inductive circuit.
Calculations and definitions for VA and true power can
be found in last month's issue.
With a handle on both capacitors and inductors in AC
circuits, a technician is ready to learn about resonance
and filters. Resonance, filters and amplification are the
key elements to making radio transmitters and receivers
operate. q

R

Z
XC

Z=

R 2 +X c2

Z=

10 2 +10 2

Z=

100+100

Z=

200

Z= 14.14 Ohms
o
= 45
Figure 3
avionics news

*

october

2019

69



Avionics News October 2019

Table of Contents for the Digital Edition of Avionics News October 2019

No label
Avionics News October 2019 - No label
Avionics News October 2019 - Cover1
Avionics News October 2019 - Cover2
Avionics News October 2019 - 1
Avionics News October 2019 - 2
Avionics News October 2019 - 3
Avionics News October 2019 - 4
Avionics News October 2019 - 5
Avionics News October 2019 - 6
Avionics News October 2019 - 7
Avionics News October 2019 - 8
Avionics News October 2019 - 9
Avionics News October 2019 - 10
Avionics News October 2019 - 11
Avionics News October 2019 - 12
Avionics News October 2019 - 13
Avionics News October 2019 - 14
Avionics News October 2019 - 15
Avionics News October 2019 - 16
Avionics News October 2019 - 17
Avionics News October 2019 - 18
Avionics News October 2019 - 19
Avionics News October 2019 - 20
Avionics News October 2019 - 21
Avionics News October 2019 - 22
Avionics News October 2019 - 23
Avionics News October 2019 - 24
Avionics News October 2019 - 25
Avionics News October 2019 - 26
Avionics News October 2019 - 27
Avionics News October 2019 - 28
Avionics News October 2019 - 29
Avionics News October 2019 - 30
Avionics News October 2019 - 31
Avionics News October 2019 - 32
Avionics News October 2019 - 33
Avionics News October 2019 - 34
Avionics News October 2019 - 35
Avionics News October 2019 - 36
Avionics News October 2019 - 37
Avionics News October 2019 - 38
Avionics News October 2019 - 39
Avionics News October 2019 - 40
Avionics News October 2019 - 41
Avionics News October 2019 - 42
Avionics News October 2019 - 43
Avionics News October 2019 - 44
Avionics News October 2019 - 45
Avionics News October 2019 - 46
Avionics News October 2019 - 47
Avionics News October 2019 - 48
Avionics News October 2019 - 49
Avionics News October 2019 - 50
Avionics News October 2019 - 51
Avionics News October 2019 - 52
Avionics News October 2019 - 53
Avionics News October 2019 - 54
Avionics News October 2019 - 55
Avionics News October 2019 - 56
Avionics News October 2019 - 57
Avionics News October 2019 - 58
Avionics News October 2019 - 59
Avionics News October 2019 - 60
Avionics News October 2019 - 61
Avionics News October 2019 - 62
Avionics News October 2019 - 63
Avionics News October 2019 - 64
Avionics News October 2019 - 65
Avionics News October 2019 - 66
Avionics News October 2019 - 67
Avionics News October 2019 - 68
Avionics News October 2019 - 69
Avionics News October 2019 - 70
Avionics News October 2019 - 71
Avionics News October 2019 - 72
Avionics News October 2019 - 73
Avionics News October 2019 - 74
Avionics News October 2019 - 75
Avionics News October 2019 - 76
Avionics News October 2019 - 77
Avionics News October 2019 - 78
Avionics News October 2019 - 79
Avionics News October 2019 - 80
Avionics News October 2019 - Cover3
Avionics News October 2019 - Cover4
http://www.brightcopy.net/allen/avne/58-4
http://www.brightcopy.net/allen/avne/58-3
http://www.brightcopy.net/allen/avne/58-2
http://www.brightcopy.net/allen/avne/58-1
http://www.brightcopy.net/allen/avne/57-12
http://www.brightcopy.net/allen/avne/57-11
http://www.brightcopy.net/allen/avne/57-10
http://www.brightcopy.net/allen/avne/57-9
http://www.brightcopy.net/allen/avne/57-8
http://www.brightcopy.net/allen/avne/57-7
http://www.brightcopy.net/allen/avne/57-6
http://www.brightcopy.net/allen/avne/57-5
http://www.brightcopy.net/allen/avne/57-4
http://www.brightcopy.net/allen/avne/57-3
http://www.brightcopy.net/allen/avne/57-2
http://www.brightcopy.net/allen/avne/57-1
http://www.brightcopy.net/allen/avne/56-12
http://www.brightcopy.net/allen/avne/56-11
http://www.brightcopy.net/allen/avne/56-10
http://www.brightcopy.net/allen/avne/56-9
http://www.brightcopy.net/allen/avne/56-8
http://www.brightcopy.net/allen/avne/56-7
http://www.brightcopy.net/allen/avne/56-6
http://www.brightcopy.net/allen/avne/56-5
http://www.brightcopy.net/allen/avne/56-4
http://www.brightcopy.net/allen/avne/56-3
http://www.brightcopy.net/allen/avne/56-2
http://www.brightcopy.net/allen/avne/56-1
http://www.brightcopy.net/allen/avne/55-12
http://www.brightcopy.net/allen/avne/55-11
http://www.brightcopy.net/allen/avne/55-10
http://www.brightcopy.net/allen/avne/55-9
http://www.brightcopy.net/allen/avne/55-8
http://www.brightcopy.net/allen/avne/55-7
http://www.brightcopy.net/allen/avne/55-6
http://www.brightcopy.net/allen/avne/55-5
http://www.brightcopy.net/allen/avne/55-4
http://www.brightcopy.net/allen/avne/55-3
http://www.brightcopy.net/allen/avne/55-02
http://www.brightcopy.net/allen/avne/55-01
http://www.brightcopy.net/allen/avne/54-12
http://www.brightcopy.net/allen/avne/54-11
http://www.brightcopy.net/allen/avne/54-10
http://www.brightcopy.net/allen/avne/54-9
http://www.brightcopy.net/allen/avne/54-8
http://www.brightcopy.net/allen/avne/54-7
http://www.brightcopy.net/allen/avne/54-6
http://www.brightcopy.net/allen/avne/54-5
http://www.brightcopy.net/allen/avne/54-4
http://www.brightcopy.net/allen/avne/54-3
http://www.brightcopy.net/allen/avne/54-2
http://www.brightcopy.net/allen/avne/54-1
http://www.brightcopy.net/allen/avne/53-12
http://www.brightcopy.net/allen/avne/53-11
http://www.brightcopy.net/allen/avne/53-10
http://www.brightcopy.net/allen/avne/53-9
http://www.brightcopy.net/allen/avne/53-8
http://www.brightcopy.net/allen/avne/53-7
http://www.brightcopy.net/allen/avne/53-6
http://www.brightcopy.net/allen/avne/53-5
http://www.brightcopy.net/allen/avne/53-4
http://www.brightcopy.net/allen/avne/53-3
http://www.brightcopy.net/allen/avne/53-2
http://www.brightcopy.net/allen/avne/53-1
http://www.brightcopy.net/allen/avne/52-12
http://www.brightcopy.net/allen/avne/52-11
http://www.brightcopy.net/allen/avne/52-10
http://www.brightcopy.net/allen/avne/52-9
http://www.brightcopy.net/allen/avne/52-8
https://www.nxtbook.com/allen/avne/52-7
https://www.nxtbook.com/allen/avne/52-6
https://www.nxtbook.com/allen/avne/52-5
https://www.nxtbook.com/allen/avne/52-4
https://www.nxtbook.com/allen/avne/52-3
https://www.nxtbook.com/allen/avne/52-2
https://www.nxtbook.com/allen/avne/52-1
https://www.nxtbook.com/allen/avne/51-12
https://www.nxtbook.com/allen/avne/51-11
https://www.nxtbook.com/allen/avne/51-10
https://www.nxtbook.com/allen/avne/51-9
https://www.nxtbook.com/allen/avne/51-8
https://www.nxtbook.com/allen/avne/51-7
https://www.nxtbook.com/allen/avne/51-6
https://www.nxtbook.com/allen/avne/51-5
https://www.nxtbook.com/allen/avne/51-4
https://www.nxtbook.com/allen/avne/51-3
https://www.nxtbook.com/allen/avne/51-2
https://www.nxtbook.com/allen/avne/51-1
https://www.nxtbook.com/allen/avne/50-12
https://www.nxtbook.com/allen/avne/50-11
https://www.nxtbook.com/allen/avne/50-10
https://www.nxtbook.com/allen/avne/50-9
https://www.nxtbook.com/allen/avne/50-8
https://www.nxtbook.com/allen/avne/50-7
https://www.nxtbook.com/allen/avne/50-6
https://www.nxtbook.com/allen/avne/50-5
https://www.nxtbook.com/allen/avne/50-4
https://www.nxtbook.com/allen/avne/50-3
https://www.nxtbook.com/allen/avne/50-2
https://www.nxtbook.com/allen/avne/50-1
https://www.nxtbook.com/allen/avne/49-12
https://www.nxtbook.com/allen/avne/49-11
https://www.nxtbook.com/allen/avne/49-10
https://www.nxtbook.com/allen/avne/49-9
https://www.nxtbook.com/allen/avne/49-8
https://www.nxtbook.com/allen/avne/49-7
https://www.nxtbook.com/allen/avne/49-6
https://www.nxtbook.com/allen/avne/49-5
https://www.nxtbook.com/allen/avne/49-4
https://www.nxtbook.com/allen/avne/49-3
https://www.nxtbook.com/allen/avne/49-2
https://www.nxtbook.com/allen/avne/49-1
https://www.nxtbook.com/allen/avne/48-12
https://www.nxtbook.com/allen/avne/48-11
https://www.nxtbookmedia.com