C203 Week 1 - Aviation - Obsidian Publish

# ATAC203 Avionics Systems > # [[C203 Intro#ATAC 203 Avionics Systems| ◀️ ]]  [[C203 Home| Home ]]  [[C203 Week 2| ▶️ ]]               [[QR C203T SSGW01| 🌐 ]] [📝](https://excalidraw.com/) ># [[C203 Week 1#ATAC203 Avionics Systems|Week 1]] >- [[#Introduction to Avionics Systems|Introduction to Avionics Systems]] >- [[#Radio Theory|Radio Theory]] >- [[#Antenna Theory|Antenna Theory]] ^ofld7w >[!jbplus|c-blue]- Lesson Intro >### What > >This week we will lay some foundations for the material that follows. > >### Why > >You may be required to work on [[Avionics]] Systems, even if you are a Maintenance Technician. Many of these systems use [[radio]] technology, and so an understanding of that will help. > >### Testing > >You will be tested on this material on Assignment 1 and the Midterm/Final. ## Introduction to Avionics Systems ### Required by Regulation [[Avionics]] Systems are required by regulation for aircraft operating in high traffic airspace. The word avionics is a combination of the words "aviation" and "electronics". ### Many systems Avionics Systems aid the pilot in flying safely from point A to point B, using the following systems: * [[ Communication Systems]] * [[Navigation Systems]] * [[Autopilot]] ^3rlvkh * [[TCAS|Collision Avoidance System]] * [[Weather Radar]] * [[Pulse Systems]] Your work on these systems is governed by the type of [[AME]] License you hold. ### Licensing #### M - Maintenance Mechanic (M1 & M2) %% C203W01Q01 %% [[M1]] mechanics may see more hands-on experience with avionics, but because of the ever increasing integration between systems that avionics allows, all aircraft technicians, including [[M2]]s must have knowledge of avionics systems. In particular, safety precautions regarding electricity must be understood and observed. [[M1andM2|😎]] #### E - Avionics Of course, avionics is the bread and butter of [[AME E license]] holders. This course is not specifically designed for these technicians, this course is aimed at maintenance students. [[Pasted image 20210213101523.png|😎]] #### S - Structure [[Structure Technicians]] are often responsible for the mounting of avionics and the associated instrumentation in the cockpit. In some cases, their expertise is required when maintaining antennae. ## Radio Theory ### The Electromagnetic Spectrum %% Q03 Q04 Q10 %% > [!aside]- Ref >[[Electromagnetic Spectrum|🗺️]] Electromagnetic [[radiation]] refers to the waves of [[electromagnetism]] that radiate throughout space carrying radiant energy. There are many sources of these electromagnetic waves (EM waves), some natural, and some man-made. These waves are synchronized [[Oscillation|oscillations]] of electric and magnetic fields. These oscillations are vibrations effectively, and they can be measured by how often they move back and forth. This, as you know, is called [[frequency]]. This oscillation movement, because it repeats, can be seen as a cycle, and frequency is the measure of how many of these cycles occur per second. #### Range of frequencies We remember from earlier courses that [[frequency]] is measured in [[Hertz|cycles per second]] . The [[electromagnetic spectrum]] covers [[electromagnetism|electromagnetic]] waves with frequencies below 1 [[Hertz|Hz]], to above 1025Hz. We will look at the relationship between frequency and wavelength shortly, but for now just know that the range when expressed as [[wavelength]]s goes from a fraction of the size of the nucleus of an atom all the way to thousands of kilometres. In fact, theoretically, the largest wavelength is equal to the size of the universe itself. ##### Bands %% Q05 Q06 Q07 %% This range of frequencies is divided into bands, and the waves in those bands are given different names. [[Electromagnetic Waves|EM waves]] are classified according to their characteristic frequencies and associated wavelength. The spectrum includes frequencies starting at 0Hz and ranging to extremely high frequencies. [[Pasted image 20201223131323.png|➡]]![[Pasted image 20201223131323.png|350]] <a href="https://commons.wikimedia.org/wiki/File:EM_Spectrum_Properties_edit.svg#/media/File:EM_Spectrum_Properties_edit.svg"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/EM_Spectrum_Properties_edit.svg/1200px-EM_Spectrum_Properties_edit.svg.png" alt="EM Spectrum Properties edit.svg"></a> <a href="http://creativecommons.org/licenses/by-sa/3.0/" title="Creative Commons Attribution-Share Alike 3.0">CC BY-SA 3.0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=2974242">Link</a> Notice in this graphic that there are two headers, one at the top for [[electromagnetism|electromagnetic]] energy, and another at the bottom for [[Sound|acoustical energy]]. It would appear that sound and electromagnetic energy share the same frequencies. What is the difference? Sound waves are mechanical waves. This mean that sound requires a medium, or some matter, to be able to [[Propagation|propogate]] or radiate. This can be the [[Molecule|molecule]] of air, or water, or other solids. Sound cannot travel through a [[vacuum]], and so sound cannot travel in space. This works out well, because if it could, the sound of the sun would make hearing on earth utterly impossible. Electromagnetic waves on the other hand are not mechanical waves, and do not require a medium in order to radiate or propagate. There are other important differences between these two types of energy, but they are beyond the scope of this course. Sound waves can be perceived by the human ear, while EM waves are perceived and processed by electronic equipment such as radio receivers. It is not clearly indicated on this graphic, but the range of human hearing is roughly between 20 Hz and 20 KHz. [[Online Learning in the 1940s|😎]] Just above this frequency range begins the [[Radio Frequency]] or RF range, our main concern for this course. Beyond that, characteristics of EM waves continue to change, and we see microwaves, light, and X-Rays. These are still EM waves, but the frequencies are very high. [[Pasted image 20210629123454.png|😎]] ##### Aviation Radio Frequency Bands %% Q11 %% > [!aside]- Ref >[[Radio Wave Band|🗺️]] %%[[Pasted image 20201223131628 7.png|➡]]![[Pasted image 20201223131628 7.png|350]]%% [[XC Aviation RF Band.dark.png|➡️]]![[XC Aviation RF Band.dark.png|350]] In this graphic, we see the [[Radio Wave Band]]. This band is further subdivided into separate radio bands. These bands are regulated. This means that it is against the law to use these frequencies except for their intended purpose. This is necessary, as there would be massive interference between waves in the same band if they did not follow some rules for their use. The governance of radio waves is supported by international agreements and laws. ### Electromagnetic Waves and Fields %% Q02 Q12 Q13 %% #### Two components: electric and magnetic ##### Polarization%%1%% %% Q14 %% [[Pasted image 20201223131804.png|➡]]![[Pasted image 20201223131804.png|350]] Electromagnetic waves are made of electric and magnetic fields, which are at right angles from each other. Fields are created when an [[alternating current]] flows in a conductor such as a transmission line or an antenna. We will see more about [[antenna]]e shortly. <a href="https://commons.wikimedia.org/wiki/File:Electromagnetic_wave2.svg#/media/File:Electromagnetic_wave2.svg"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Electromagnetic_wave2.svg/1200px-Electromagnetic_wave2.svg.png" alt="Electromagnetic wave2.svg"></a> <a By <a href="//commons.wikimedia.org/w/index.php?title=User:Francois~frwiki&amp;action=edit&amp;redlink=1" class="new" title="User:Francois~frwiki (page does not exist)">Francois~frwiki</a> - Own work, href="https://creativecommons.org/licenses/by-sa/4.0" title="Creative Commons Attribution-Share Alike 4.0">CC BY-SA 4.0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=108645646">Link</a> EM wave Magnetic & Electric fields are at right angles (90 deg) to each other, as they travel or radiate after they have become detached from the antenna. An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular. By convention, the [[polarization]] of electromagnetic waves refers to the plane of the electric field. #### Electromagnetic Wave Propagation %% Q08 Q09 Q15 Q16 Q17 %% [[Pasted image 20201223132134.png|➡]]![[Pasted image 20201223132134.png|350]] [[Electromagnetic Waves|EM waves]] propagate through the air at effectively the speed of light (They do not travel at precisely the speed of light, but we can use this as a reference for our purposes). The wave is generated by a [[transmitter]], which is then fed to the antenna for [[propagation]]. The wave can be received by a receiver antenna, which captures the EM waves, and through induction produces a varying current which is then fed to the receiver circuitry. Remember from [[T105 Week 9#Inductance|Basic Electricity]] that a voltage is induced in a conductor when it crosses line of [[electromagnetism|electromagnetic]] flux. This property of electricity is applied here, the [[voltage]] being induced by the [[Radio Wave]] as it passes over the antenna, which is a conductor. This induced voltage produces a current into the receiver circuit. Q: Given that radio waves travel at (almost) the [[speed of light]], can you estimate how long it would take for the radio signals used to control the Mars Lander Perseverance to travel from Earth to Mars? [[Ultra-High Frequency Antenna|Answer]] [[Pasted image 20201223132432.png|➡]]![A Basic Radio System (2)|350](<Pasted image 20201223132432.png>) The above graphic is just a different way to show a basic radio system. As for Basic Electricity, you will have to have your own mental image of how these things work, as they are not visible to the human eye. ### Categories of EM Waves [[Electromagnetic Waves|EM waves]] are categorized into 3 different categories which are based on their frequencies: - Ground Wave - Sky Wave - Space Wave Each of these categories are characterized by how they behave as they travel through the earth's [[atmosphere]]. [[Q001|❓]] #### Ground Wave %% Q18 Q19 Q21 %% > [!aside]- Ref >[[Ground Wave|🗺️]] [[Pasted image 20201223133039.png|➡]]![[Pasted image 20201223133039.png|left|250]] Waves in the HF band, that is, RF below 3 MHz, fall into the category of ground waves: Ground waves follows the curvature of the earth surface as they travel through the [[atmosphere]]. #### Sky Wave %% Q20 %% > [!aside]- Ref >[[Sky Wave|🗺️]] [[Pasted image 20201223133229.png|➡]]![[Pasted image 20201223133229.png|left|250]] Sky waves are RF waves between 3 to 30MHz that tend to travel in straight lines and do not follow the curvature of the earth. They also bounce-off the [[ionosphere]] (ionized layer). This extends the range of the wave. #### Space Wave %% Q23 %% > [!aside]- Ref >[[Space Wave|🗺️]] [[Pasted image 20201223133423.png|➡]]![[Pasted image 20201223133423.png|left|250]] Space waves are comprised of RF above 30MHz and tend to travel in straight lines and do not follow the curvature of the earth. They do not bounce-off the [[ionosphere]], they penetrate it. ### Modulation %% Q24 Q25 Q26 Q36 Q37 Q38 Q39 Q40 q52 %% > [!aside]- Ref >[[Modulation|🗺️]] #### One wave modifies another * Modulating signal * [[Carrier]] Modulation is the process of varying one or more properties of an EM waveform, called the [[carrier]] signal, with a modulating signal that typically contains information to be transmitted. The nature of [[audio]] waves, that is, [[Electromagnetic Waves|EM waves]] in the audio band, is such that it takes great power to transmit them long distances. Higher frequency [[Radio Frequency|RF]] is much more suitable for transmission over long distances. So, modulation is a way to take advantage of the the nature of RF waves to carry [[audio]] or other signals. One example that might make sense to you is the sound at a large concert. To transmit sound waves at frequencies that our ears can hear takes a great deal of power for even a short distance. A rock concert may require 10s of thousands of watts to transmit the sound in a venue, and even more if the concert is outside. That same music can be broadcast over an entire city when radio frequencies are used as a carrier, and requires much less power. The lower the frequency, the more power that is required. Have a look at how much energy is required to ring a bell of a low note: [[Low Bell|🎞️]] #### Three most common forms of modulation %% Q27 Q28 Q29 Q30 Q31 Q32 Q33 Q34 Q35 %% The three most common forms of modulation are amplitude modulation ([[AM]]), frequency modulation ([[FM]]) and [[pulse modulation]]. As their names imply, they accomplish modulation of the carrier wave in different ways. [[Pasted image 20201223134727.png|➡]] ![[Pasted image 20201223134727.png|350]] ##### AM > [!aside]- Ref >[[AM|AM]] In AM, the signal to be carried is used to modify the [[amplitude]] of a [[carrier]] wave of a constant [[frequency]]. ##### FM > [!aside]- Ref >[[FM|🗺️]] In FM, the signal to be carried is used to modify the [[frequency]] of the [[carrier]] wave, which is at a constant [[amplitude]]. In this graphic you can compare the two in action: <a href="https://commons.wikimedia.org/wiki/File:Amfm3-en-de.gif#/media/File:Amfm3-en-de.gif"><img src="https://upload.wikimedia.org/wikipedia/commons/a/a4/Amfm3-en-de.gif" alt="Animation of audio, AM and FM modulated carriers."></a>By <a href="https://ru.wikipedia.org/wiki/User:Berserkerus" class="extiw" title="ru:User:Berserkerus">Berserkerus</a> - Own work, <a href="https://creativecommons.org/licenses/by-sa/2.5" title="Creative Commons Attribution-Share Alike 2.5">CC BY-SA 2.5</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=5071748">Link</a> ##### Pulse Digital modulation, or [[pulse modulation]], is a more complicated technology, but the concept is quite simple. The [[carrier]] is modified such that it indicates a 1 or a 0. The complexities of [[analog signal]] signals are reduced to two states. These modified carrier waves are transmitted via a [[transmitter]] and [[antenna]] and are in turn picked up by a receiving antenna and [[receiver]]. In the receiver circuitry is used to separate the signal from the carrier, and [[amplification|amplify]] it for various uses. ^f41fs2 ![[XC Aviation RF Band.dark.png|350]] [[XC Aviation RF Band.dark.png|➡️]] Notice in this previously seen graphic the bands that are used for [[AM]] and [[FM]]. Since AM uses only a single frequency, it can be used at lower frequencies and still have many slots or usable frequencies for many stations. FM, on the other hand, since it modulates its frequency uses a range of frequencies, and therefore requires more [[bandwidth]]. For this reason, FM is higher on the frequency spectrum. To put it another way, the AM band is from 535 KHz to 1705 KHz. This is a range of a little over 1000 KHz. The FM band is from 88 to 108 MHz, which is a range of 20 MHz. So, there are many more frequencies in the FM band, which is necessary because each station uses a range of frequencies to transmit audio. We won't get into this, but television broadcast (until recently) used both AM and FM, AM for the video, and FM for the audio. You can imagine that this is a more complex waveform, and because of the use of FM, requires a fair range of frequencies. Therefore, television broadcast is also in the [[VHF]] and [[UHF]] ranges. In fact, the FM range sits in the middle of the TV range. This of course is rapidly changing, and digital transmission, satellites, and cable have all brought improvements over the very near obsolete TV RF broadcast technology. ## Antenna Theory %% Q41 Q42 %% > [!aside]- Ref >[[Antenna|🗺️]] ### Induction Theory You have [[Inductance|already seen]] in that when electrical current travels through a conductor, a magnetic field is created around the conductor. When there is relative motion between a magnetic field, and a [[conductor]], a current flow will be induced in the conductor. #### Like a transformer (sort of) An antenna is a conductor, used to [[radio transmission|transmit]] and receive radio signals. A transmitting antenna radiates electromagnetic energy. A receiving antenna has a current flow induced in it when electromagnetic energy (radio waves) pass over it. You could compare this to the two sides of a transformer, and imagine that the primary of the transformer is the transmitting antenna, and the secondary is the receiving antenna. It is the same effect, but in reverse. Same with antennas transmitting and receiving. ### Frequency and Wavelength %% Q43 Q44 Q45 %% We know that [[frequency]] and [[period]] are inversely proportional, which is to say that the higher the frequency, the shorter the period. As mentioned, we can say for our purposes that electromagnetic energy travels at the same speed as light. So, if the amount of time is shortened, the distance the EM wave is travelling is also shortened. Imagine you are holding a rope tied to a tree and you are shaking it up and down. If you shake it faster, the wave shape of the rope will become more shallow. Its [[wavelength]] decreases as its frequency increases. Without getting into the math, if you multiply the frequency by the wavelength, you will always have the constant speed (we said speed of light, it's more complicated than that). For our purposes, we can say that frequency and wavelength are inversely proportional. Another way to state that is to say that they are reciprocal. The formula makes this clear: $f=\frac{1}{w}$ Why do we need to understand this? Because the frequency has a direct effect on wavelength, we naturally will be dealing with different wavelengths as we move through the RF spectrum. <a href="https://commons.wikimedia.org/wiki/File:Dipole_receiving_antenna_animation_6_800x394x150ms.gif#/media/File:Dipole_receiving_antenna_animation_6_800x394x150ms.gif"><img src="https://upload.wikimedia.org/wikipedia/commons/d/dd/Dipole_receiving_antenna_animation_6_800x394x150ms.gif" alt="Dipole receiving antenna animation 6 800x394x150ms.gif"></a> %% By <a href="//commons.wikimedia.org/w/index.php?title=User:Chetvorno&amp;action=edit&amp;redlink=1" class="new" title="User:Chetvorno (page does not exist)">Chetvorno</a> - Own work, <a href="http://creativecommons.org/publicdomain/zero/1.0/deed.en" title="Creative Commons Zero, Public Domain Dedication">CC0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=40789783">Link</a> %% In order for an antenna to work, it has to "feel" the full [[radio transmission|transmission]]. The ideal length for an antenna is one half of the wavelength being transmitted or received. Half wave antennas are not practical for aircraft use, so $\frac{1}{4}$ wavelength antennas are commonly used. What is key for you to understand is that antenna size has everything to do with the frequency being used. Higher frequency radio signals require shorter antennas. Lower frequencies require larger antennas. ### Impedance matching %% Q46 Q47 Q48 %% > [!aside]- Ref >[[Faculty/Student/References/Glossary/Impedance Matching|🗺️]] [[Impedance]], as you have learned, is the complex result of [[resistivity|resistive]] and [[reactance|reactive]] elements in an electrical circuit. We do not have to go much deeper here than to say that: * Maximum Power transfer between a [[transceiver]] and an [[antenna]] will occur when the impedance of the antenna system matches the impedance of the transceiver. Most aircraft antennas, and antenna [[coaxial]] cables have an impedance of $50 \Omega$. We cover this only briefly because the message will be repeated elsewhere. You must understand that in avionics, the mechanical connection is not the whole story. The electrical connections have characteristics that may well be invisible, and critical to the operation of the equipment. You absolutely must respect the specifications of avionics equipment, and go "by the book" always. ### Polarization Refer to this [[Pasted image 20201223131954.png|image previously seen]] with both [[Electricity|electric]] and [[Magnetism|magnetic]] waves. You see that there is a 90° difference between the two. This means the wave "hits" an antenna at different orientations. When they are matched, the maximum wave power is felt by the antenna. When they are not, very little power is induced in the [[antenna]]. This is very much like the [[armature]] of a [[generator]] as it passes through the flux lines. There also there is a maximum power transfer when the most lines of flux are crossed, and minimum when they are aligned. This effect in antennas is called [[polarization]]. In order for a [[receiver]] to receive a radio signal, its antenna must be of the same [[polarization]] orientation as the transmitting antenna. Aircraft radio systems employ both horizontally, and vertically polarized antennas. [[Pasted image 20201223142818.png|➡]]![[Pasted image 20201223142818.png|350]] In this graphic, the antenna generating this wave is vertical. When we compare the orientation of the antenna to the wave, we are referring to the electrical wave portion. ### Ground Plane %% Q50 Q51 %% >[!aside]- Ref >[[ground plane|🗺️]] A [[ground plane]] is a conducting surface which is large in comparison to the [[wavelength]]. It is connected to the [[radio transmission|transmitter]]'s ground wire, and serves as a reflecting surface for [[radio wave]]s. This is another area of radio technology that gets complicated fast. We can simply say: * In order to operate properly, an antenna requires a Ground Plane. Most aircraft antennas use the skin of the aircraft as their ground plane. For this reason, proper [[Electricity|electrical]] [[bonding]] must occur between the base of an antenna, and the skin of the aircraft. This should be inspected whenever removing and replacing an antenna. You may never get to the bottom of the technology that requires this, but now you know enough that when a tech manual specifies how an antenna is to be connected, there is an important operational reason for it. It is also why parts like this may not be interchanged. They are electrically significant. The base of an aircraft antenna should be sealed with the proper sealant to prevent [[contamination]] and [[corrosion]]. Again, you may not assume that any sealant will do the job. The properties of the sealant are taken into account when designing antennae, and you must respect the [[specifications]]. Aircraft which do not have metal skin may require a special "Ground Plane Plate" to be manufactured and installed at the base of the antenna. Conclusion %% #JBTODO %% It is important that you now proceed to the weekly practice quiz in the courseshell on eCentennial. You will find this is the fastest way to ensure that you are on top of the material, ready to move forward in the course, and ready for testing. > # [[C203 Home| ◀️ ]]  [[C203 Home| Home ]]  [[C203 Week 2| ▶️ ]]     [[QR C203T SSGW01| 🌐 ]]    [[FB C203|Please Help]]