# ATAC203 Avionics Systems > # [[C203 Week 1| ◀️ ]] &nbsp;[[C203 Home| Home ]] &nbsp;[[C203 Week 3| ▶️ ]] &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; [[QR C203T SSGW02| 🌐 ]] [📝](https://excalidraw.com/) ># [[C203 Week 2#ATAC203 Avionics Systems|Week 2]] >- [[C203 Week 2#Superheterodyne Receivers|Superheterodyne Receivers]] >[[C203 Week 2#🔹Mandatory Project 203-1 Superheterodyne Block Diagram|🔹Mandatory Project 203-1 Superheterodyne Block Diagram]] >- [[C203 Week 2#Principles of Navigation|Principles of Navigation]] ^f252ce > [!jbPlus|c-blue]- Lesson Intro >### What > >This week we will be looking at two different topics, both fundamental for other material in this course. > >### Why > >Superheterodyne receivers appear in many of the systems we will look at, and basic navigation concepts will help you to understand functions and displays of many of these systems.. > >### Testing > >You will be tested on this material on Graded Quiz 2 and the Midterm/Final. > >### Approach and Objectives > >By understanding the following topics, you will have achieved the learning outcomes for this lesson. Consult your course outline for the learning outcomes and other details of this course. ^6005a2 ## Superheterodyne Receivers > [!aside]- Ref >[[Superheterodyne|🗺️]] ### Definition of Superheterodyne %% Q01 Q02 Q03 Q04 Q05 Q06 Q07 Q08 Q09 Q10 %% You may think that superheterodyne is better than [[heterodyning|heterodyne]]. This is not the case. Here is the actual etymology: The term superheterodyne is made of three parts: - **Super** - meaning supersonic, that is, above the frequency range of audio. - **Hetero** - from the Greek word for "different" - **Dyne** - from the Greek word for "power" The term was coined by Canadian Reginald Fessenden who pioneered the [[heterodyning|heterodyne]] detector in 1905. It refers to the process of mixing different radio [[Frequency|frequencies]] (rather than power) so that a received radio signal can be converted to an intermediate frequency (IF) This IF can be more efficiently processed than the higher [[radio transmission|transmission]] frequency. In this lesson we will examine a block diagram of a simple generic superheterodyne receiver, but this technology, with variations, is in use in virtually all modern radio [[receiver|receivers]]. Also note that its use goes beyond [[broadcast]] radio, and is used in many radio-based [[navigation]] aids as well. ### Frequency Mixing %%==[[Faculty/Student/Content/C203/Master QB#Q00064|Q]]==%% > [!aside]- Ref >[[Frequency Mixing|🗺️]] The superheterodyne principle of operation of the receiver depends on the use of [[heterodyning]] or frequency mixing. #### Purpose of Superheterodyning If we only had to deal with one [[radio transmission]] [[carrier]] [[frequency]], we could buy the [[Component|components]] required to build an optimum circuit for that frequency, and all would be well. Remember from [[T105 Week 12#Impedance|basic electricity]] how [[coil|inductors]] and [[capacitor]] would offer minimal [[impedance]] at the [[T105 Week 12#Resonance in an AC Circuit|resonant frequency]]. This is how you could build or tune a circuit for a specific frequency. The problem is when we want to be able to tune into different frequencies. As we will see, this would require that all of the frequency based circuits in the receiver would have to be tunable, and this causes difficulties including more weight and expense. #### Mixing frequencies produces a third frequency %%==[[Faculty/Student/Content/C203/Master QB#Q00065|Q]]==%% >[!aside]- Ref [[Faculty/Student/References/Glossary/Frequency Mixing|🗺️]][[beat frequency|🗺️]] When two frequencies are mixed, the result is a combination of the original two frequencies and two new frequencies: the [[sum]] of the two frequencies, and the [[difference]] between the two. The difference between the two frequencies produces what is called a [[beat frequency]], which is demonstrated below. [[Pasted image 20201227214113.png|➡]]![[Pasted image 20201227214113.png|350]] [[WaveInterference.gif|➡]]![[WaveInterference.gif|350]] #### Audio Demonstration Beat frequencies can be demonstrated in the [[audio spectrum]] with the use of a tone generator. Either [this link](http://onlinetonegenerator.com/) or [this link](https://www.szynalski.com/tone-generator/) will allow you to do this experiment yourself, which is highly recommended. Open two tabs with the same link, and set one to 440Hz and the other to 442 Hz. Play both at the same time and notice the "beat" that is produced, a sound that clearly pulses twice per second. What you are hearing is the first wave, the second wave, and a third wave that has a frequency of (f1 + f2)/2 and whose volume varies at a frequency equal to the difference between the two. This growing and decreasing volume is the result of waves alternately interfering constructively (they add together) and destructively (one subtracts from the other). - Let's recap: We hear 440Hz, 442Hz, and 2Hz. 2Hz is the [[beat frequency]]. Now let's try something else that will help you to understand superheterodyning. If we set the first tone generator 600Hz, and the second one to 602Hz, notice the beat frequency is the same, that is, 2Hz. - Let's recap again: Now we hear 600Hz, 602Hz, and 2Hz. The beat frequency is the same. This is a key concept. By mixing two frequencies, we can output a [[beat frequency]]. If we change the two frequencies, but the difference between them is the same, the beat frequency is also the same. This has important implications. This demonstration is only for you to understand and experience how two frequencies can produce a very complicated result. Remember that the experiment was done with audio waves so that you could hear the results. Radios use [[Radio Frequency|RF]] of course, and so is not audible, but governed by the same principles. #### Tune for the beat %%==[[Faculty/Student/Content/C203/Master QB#Q00066|Q]]==%% The whole point of understanding beat frequencies is to realize that we can produce whichever beat frequency we want if we add a second frequency that differs by the frequency of the beat. As we saw in our demo, when we had a 440 Hz wave, to get a 2 Hz beat, we added a 442 Hz wave. To get that same 2 Hz wave when we had a 600 Hz wave, we had to add a 602 Hz wave. This concept led to a revolution in [[radio]] which is seen in virtually every radio today. A radio could be designed for a specific frequency, with the [[Component|components]] and circuitry perfectly optimized for highest performance. To tune the radio to several frequencies, we only need to add signals of different frequencies. Once the beat is created by this mixing, the rest of the radio processes the beat frequency only, and therefore treats each and every incoming frequency exactly the same. In radio circuitry, this beat frequency is known as the [[intermediate frequency]], often abbreviated to IF. It is called intermediate, because it is between the [[Radio Frequency|RF]] frequencies of the [[radio transmission|transmission]] and the [[audio frequencies]] they carry by modulation. ### Superheterodyne Principles of Operation Now that we know a little about the effects of frequency mixing, we will look at a complete superheterodyne receiver at the [[Block Diagram]] level. In case you are not familiar with block diagrams, they are a high level graphical depiction of [[electronic]] functionality. They will not show you [[Component|components]] or wires, but rather will describe what happens in various parts of a complicated piece of electronic equipment. They are very useful not only for learning, but also for [[troubleshooting]]. We will follow a radio signal that has been transmitted through the air, and see what happens when it arrives at our radio receiver. [[Superhet Block Diagram.png|➡️]] #### Antenna %%==[[Faculty/Student/Content/C203/Master QB#Q00067|Q]]==%% [[Antenna and signal.png|➡️]] The [[antenna]], which is the proper size for the [[frequency]] range we wish to receive, has a current [[induction|induced]] in it from the transmitted modulated [[Radio Frequency|RF]] waves. This is a miniscule amount of [[current]], usually measuring only microamps. Note that it will receive all [[Radio Frequency|RF]] waves in the range it is suitable for. Notice the symbol for the antenna. #### [[Radio Frequency|RF]] Filter [[RF Filter and Signal.png|➡️]] This stage [[filter|filters]] out the frequencies that we do not want. This stage is adjustable, and is what is affected when you tune a receiver to a certain station using the [[Control Head]] . The names of the blocks are helpful. This block filters the [[Radio Frequency|RF]] so that we get the frequency we want, i.e. the station we are tuning to. #### [[Radio Frequency|RF]] Amplifier %%==[[Faculty/Student/Content/C203/Master QB#Q00068|Q]]==%% [[RF Amp and Signal.png|➡️]] Since the signals we are dealing with are very small, we [[amplify]] them before the processing that is to follow, making them more robust while being manipulated. Again, note that the name of the block describes both which kinds of frequencies are being dealt with ([[Radio Frequency|RF]] ) and what is being done ([[amplification]]). Improved components have resulted in much more sensitive circuitry that can do a good job even on very small signals, and so the [[Radio Frequency|RF]] amplifier stage is sometimes omitted in modern designs. #### Local oscillator %%==[[Faculty/Student/Content/C203/Master QB#Q00063|Q]]==%% [[LO and Signal.png|➡️]] The local [[oscillator]] (LO) will produce a pure [[sinusoidal]] [[Radio Frequency|RF]] frequency that when mixed with the incoming modulated [[Radio Frequency|RF]] will produce an Intermediate Frequency ([[IF]]) that will be a fixed frequency for all input frequencies. This adjustment is done in conjunction with the [[Radio Frequency|RF]] [[filter]] stage. Note the dotted lines in the [[Block Diagram]] that show the [[Radio Frequency|RF]] Filter and the Local Oscillator are both adjusted depending on the frequency selected on the [[Control Head]]. These controls are ganged, which is to say, they both must be tuned appropriately for the desired incoming station. See that the tuning of the radio is accomplished by changing the frequency of the local oscillator (The [[Radio Frequency|RF]] filter is simply tuned with it to accept only the desired station). The tuning of the radio is now complete. No other circuitry requires tuning thanks to the use of the IF. #### Mixer %%==[[Faculty/Student/Content/C203/Master QB#Q00087|Q]]==%% [[Mixer and Signal.png|➡️]] The [[faculty/student/references/glossary/Frequency Mixing|mixer]] takes the incoming [[Modulation|modulated]] [[Radio Frequency|RF]] and mixes it with the [[Radio Frequency|RF]] from the LO, creating a number of output frequencies: The original two frequencies, the sum and the difference. The sum and difference frequencies will vary exactly according to the original modulation. The difference frequency is our IF. This IF is modulated exactly like the input, only the carrier frequency has changed to the IF. #### IF Filter [[IF Filter and Signal.png|➡️]] Again, a descriptive block name. This stage takes the many [[waveform|waveforms]] from the mixer, and filters out all except the difference waveform, which is now a lower frequency, the [[intermediate frequency]]. It is a lower frequency because it is the difference between the modulated [[Radio Frequency|RF]] and the LO pure [[sinusoidal|sine wave]]. This new carrier frequency is modulated, as it is the result of mixing the modulated [[Radio Frequency|RF]] from our station with the LO. The original [[Radio Frequency|RF]] signal, the LO RF, and any other frequencies (other [[harmonics]] are also generated, not covered on this course) are now taken out of the signal path, their job being done. The result is an IF that is modulated with the original modulation. #### IF Amp [[IF Amp and Signal.png|➡️]] This [[amplification|amplifier]] takes our modulated IF and boosts it to the correct levels required by the [[Demodulator]]. #### Demodulator %%==[[Faculty/Student/Content/C203/Master QB#Q00088|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00089|Q]]==%% [[Demod and Signal.png|➡️]] We now can remove the [[audio signal|audio]] that was used to [[Modulation|modulate]] our original transmitted [[Radio Frequency|RF]] from the IF. Once again, we are always dealing with the same IF, so this circuitry is optimized for a very tight range, making it more efficient. The IF is now stripped from the wave, and we are left with only the modulation, or the audio that was used to modulate the signal at the [[transmitter]]. The process of stripping the audio from the carrier is actually achieved by measuring. In the case of [[AM]], the [[amplitude]] is measured by the [[demodulation]] circuitry, and the graph of the amplitude measurements is the resultant audio. FM is the same concept, except a higher frequency will correspond to a higher amplitude in the resultant audio waveform. The diode symbol simply indicates that a diode is used in the process of extracting audio from the intermediate frequency wave. #### Audio Amplifier [[Audio Amp and Signal.png|➡️]] This audio now requires [[amplification]] so that it can drive headphones or speakers. #### Audio Output [[Audio Out and Signal.png|➡️]] [[Speakers]] or [[headphones]] will now actually move air molecules and the original signal is heard. #### Conclusion If we could not use an IF this way, then the IF filter would have to also be tuned to a constantly changing input frequency, or we would have to be able demodulate any frequency in the band, therefore requiring more tunable circuits. Superheterodyning allows this stage to be built for one frequency only, and tuned to a very tight range, increasing its efficiency, performance and accuracy. Rather than have circuitry that could filter a wide range of frequencies, it is purpose built strictly for the IF. The advantages of superheterodyne receiver are many. Another key one is that by reducing the operating frequency from RF, lower frequency components can be used, and in general, cost is proportional to frequency. [[Radio Frequency|RF]] gain at 40 GHz is expensive, IF gain at 1 GHz is cheap as dirt. ## 🔹Mandatory Project 203-1 Superheterodyne Block Diagram [[Superhet Block Diagram.png|➡️]] - Draw a Superheterodyne block diagram. - As per example. Variations are acceptable if all the elements are present. - You may use a computer graphic app or program, or draw on paper and take a photo or scan. [This browser based software](https://excalidraw.com/) is free and easy to use. Remember to export as .png so that your submission will be readable by eCentennial. ^h9kpmy ### Required Elements: - Briefly describe the function of each block - e.g. [[Radio Frequency|RF]] amplifier: amplifies the modulated [[Radio Frequency|RF]] from the antenna - Identify types of waveforms between each stage - e.g. Output of antenna: modulated [[Radio Frequency|RF]] - Include a small graphic of each waveform between each stage - Name, Section, Date at top right. Put your name in the filename as well. Submit via dropbox at Assessments/Assignments in the course shell on eCentennial. - **Due by end of Week 5** ## Principles of Navigation >[!aside|clean]- Ref >[[Navigation|🗺️]] In order to understand the [[avionics]] systems that we are going to look at, you need to know some fundamentals about navigation and what these systems do to enable it. ### Purpose Navigation is the process of piloting an aircraft from one geographic position to another while monitoring one's position as the flight progresses. This is very much the same as navigating your car, except the maps are little more complex, with different information on them. ### Charts An [[aeronautical chart]] is much like a road map, but with information important to pilots, such as location of airports, [[beacon]]s, [[nav aids]] and hazards. [[Pasted image 20201227221014.png|➡]]![[Pasted image 20201227221014.png|350]] #### Latitude and Longitude The planet is split into imaginary slices both vertically and horizontally to allow us to describe the location any place in the world with accuracy. To do this, we require references. ##### Latitude >[!aside]- Ref >[[Latitude|🗺️]] The equator is the "0 Degree" reference for latitude. Lines of latitude are measured in degrees North and South of the equator. The North Pole is 90 degrees North, the South Pole 90 degrees South. ###### Parallel to the equator and each other [[Latitude]] lines are parallel to the equator and are equal in width. They are sometimes in fact referred to as parallels. Canada has a 3,500 Km border with the United States that runs along the 49th parallel. It is understood that this is the 49th north parallel. ##### Longitude >[!aside]- Ref >[[Longitude|🗺️]] [[Longitude]] is the measurement east or west of the prime meridian. Longitude is measured by imaginary lines that run around the Earth vertically (up and down) and meet at the North and South Poles. These lines are known as meridians. Meridians of longitude (running north-south) are divided and measured in degrees East (180) and West (180) of the Prime Meridian. The prime meridian situated in Greenwich, England is the 0° reference. ###### Meet at the Poles Lines of longitude are not equal in distance from each other and run narrower until they meet at the poles. ##### The Use of Degrees Degrees express angular displacement. In this case, the angles represent displacement in the sphere of the planet. To express a position, a cartesian coordinate system is used. The [[Cartesian]] , or rectangular , coordinate system consists of a horizontal x-axis and a vertical y-axis. The point where the axes cross is called the origin . Any point can be described as the distance it is from the origin along the x-axis and along the y-axis and is written as (x, y). Degrees of latitude and longitude may be further divided to achieve more precision. The original way resembles our divisions of time, and in fact, use the same terms. A minute represents a division of a degree into 60, and seconds are another division by 60. You will also encounter a decimal system to give more precision. Here, each successive division is by 10, and is simply represented by digits to the right of the decimal point. To express the location of Ottawa, we first describe its latitude, and then its longitude: >Ottawa is situated at 45° N, 75° W. On this graphic, you see the location that we derived by going north from the equator 45° and then going west from the Prime Meridian 75°: ![[Ottawa degrees.dark.png|350]] As you can see, while this does put us close to Ottawa, the location we are describing is a large area. To describe this more precisely, we can specify the minutes: >Ottawa is situated at 45°25' N, 75°40' W. ![[Ottawa minutes.dark.png|350]] And for more precision yet, we can use seconds: >The Peace Tower, the front door of the parliament, is situated at 45° 25' 29" N, 75° 41' 58" W. ![[Ottawa seconds.dark.png|350]] If you right click on a location in Google Maps, you will be shown the coordinates in decimal notation: ![[Ottawa Decimal.dark.png|350]] ##### Nautical Mile > [!aside]- Ref >[[Nautical Mile|🗺️]] Originally a Nautical Mile was defined as one minute of latitude (the standard is different today). Knowing this, we can describe the areas we have just seen when discussing precision in regards to geographical positions. When using degrees only, the position we are describing is an area of 60NM by 60NM. When we add the precision of minutes, we are describing an area that is 1NM by 1NM. In reference to today's standard of a nautical mile (1852m), the use of seconds gives us a square of 30m by 30m. You can quickly get coordinates from [🌍Google Earth](https://earth.google.com/web/search/Parc+Downsview+Park,+Canuck+Avenue,+North+York,+ON/@43.74829224,-79.47469338,190.55899503a,400.79159094d,35y,-154.3610533h,67.95813323t,0r/data=CigiJgokCYmaUv1WvUZAEU9WFKGHj0ZAGRSuJC1k1VLAIXqypSdtDVPA) if you enable the showing of grid lines: [[Google Earth Menu 1|➡️]][[Google Earth Menu 2|➡️]][[Google Earth Menu 3|➡️]] #### Compass %%==[[Faculty/Student/Content/C203/Master QB#Q00073|Q]]==%% [[Pasted image 20201227221850.png|➡]]![[Pasted image 20201227221850.png|]] A [[compass]] is used to determine and define direction. It measures angular displacement, clockwise from north. In other words, when you are travelling east, you are at a 90° angle from North. When navigating from one point to another the pilot uses a compass to determine direction of travel. The [[compass North]] indicator always points toward the [[Magnetic North]] . The aircraft indicator in the centre indicates the position of the aircraft against the rose which moves in sync with the planet. The compass rose typically has major demarcations such as North, East, South and West, and these are known as the [[cardinal directions|cardinal points]] >Heading indication: North (000), East (090), South (180), West (270) ![[Compass Rose]] #### Earth's Magnetic Field ##### Magnetic North vs True North You may have noticed that we said the compass points to magnetic north. This refers to the magnetic poles of the earth. [[Pasted image 20201227222018.png|➡]]![[Pasted image 20201227222018.png|]] The Earth's magnetic field is similar to that of a bar magnet tilted 11 degrees from the spin axis of the Earth. [[Pasted image 20201227222034.png|➡]]![[Pasted image 20201227222034.png|]] [[True North]] is the North you will find on a map, the result of a mathematical division of the earth. [[Magnetic North]] on the other hand is not in the same place. The earth's magnetic field has variations and is not uniformly magnetized. So, True & Magnetic North are not co-located, and are not the same thing. ##### Variation/Declination The difference between these two locations is called variation, which is the angle between true north and magnetic north. It is expressed as east variation or west variation depending upon whether magnetic north (MN) is to the east or west of true north (TN). Variation is also known as [[declination]]. The location of the north pole changes over time, so the lines of magnetic flux around the planet also change. The rate of change depends on location and how far from the poles the location is. It could change as little as 2-2.5 degrees every hundred years or so, or much more. For example, in Ivujivik, the declination may change by 1 degree every three years. In San Francisco, magnetic north is about 14.3 degrees east of true north, with the difference decreasing by about 6 minutes of arc per year. #### Heading Corrections We have seen that there is a difference between [[magnetic north]] and [[true north]]. But there is another complication. A compass is simply a [[magnet]] on a spinning needle, and it is prone to being attracted to ferrous material. In an aircraft, there is a variety of magnetic interruptions caused by [[Metal]]s and electrical circuits. This will pull the compass needle away from the real magnetic north. Luckily, it will do this in a predictable way, as the aircraft configuration does not change much. So, we now have three types of North: * TN: True North * MN: Magnetic North * CN: Compass North ##### Deviation <p class="stickies" > Do not confuse Deviation and Declination </p> [[Compass North]] is where an individual compass points north. However, because of magnetic interference from aircraft metal and electrical components, a compass may deviate from indicating correctly. This angular difference is known as [[deviation]]. [[Pasted image 20201227222312.png|➡]]![[Pasted image 20201227222312.png|350]] A compass deviation card is therefore created for each aircraft, as a result of the annual compass swing performed on the aircraft. This process involves parking the aircraft at precisely magnetic north, and noting the difference in where the compass in the cockpit is pointing. This is repeated at other points around the compass. The term compass swing refers to the aircraft being swung around the entire circle. The deviation from a compass deviation card compensates the magnetic course unique to that aircraft's compass system, which is affected by localized magnetic influences. ### Heading and Bearing [[Pasted image 20201227222433.png|➡]]![[Pasted image 20201227222433.png|350]] #### Heading %%==[[Faculty/Student/Content/C203/Master QB#Q00266|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00055|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00056|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00057|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00060|Q]]==%% The direction which the nose of the aircraft is pointed is the [[heading]]. It is given in relation to magnetic north. So, an aircraft on a heading of 180° is flying due south. This is also referred to as a [[magnetic heading]]. #### Bearing %%==[[Faculty/Student/Content/C203/Master QB#Q00077|Q]]==%% The [[bearing]] is the direction between two objects, such as an aircraft, and a radio beacon. There are two types of bearings. ##### Magnetic Bearing %%==[[Faculty/Student/Content/C203/Master QB#Q00078|Q]]==%% [[Magnetic bearing]] is the direction an object is in relation to another object, from Magnetic North. ##### Relative Bearing %%==[[Faculty/Student/Content/C203/Master QB#Q00079|Q]]==%% [[Relative Bearing]] is the direction an object is in relation to aircraft heading. ### Waypoints and Tracking #### Waypoints >[!aside]- Ref [[Waypoint|🗺️]] Waypoints are specific positions along a flight plan/path, identified by [latitude] and [[longitude]]. Waypoints can be used to confirm correct flight plan execution. Waypoints may be a simple named point in space or may be associated with existing [[navigational aid|nav aids]], intersections, or fixes. A waypoint is most often used to indicate a change in direction, speed, or altitude along the desired path. Often, this is also the pilot's cue to change frequencies for comm or nav purposes. If you give directions to someone, and tell them to turn left at the brown building, and right at the stop sign, you are using waypoints. #### Tracking The main complication when tracking is the effect of [[wind]]. Otherwise, we would simply point the aircraft where we want to go, and everything would be fine. Refer to these graphics for the following terms. This first one is what happens if the pilot does not correct for wind: ![[Tracking Terms no correction.dark.png|350]] And in this one, what happens in flight to ensure the desired track is the actual track: ![[Tracking Terms Correction.dark.png|350]] ##### Desired Track The [[desired track]] or desired course is a straight line drawn between two waypoints. ##### Track or Actual Track The track, or [[actual track]], or course, or actual course is the path of the aircraft over the ground. ##### Drift angle To maintain a desired track, it may be necessary to "crab" the aircraft. Those of you who are fans of the sport know what drifting is. Aircraft do it all the time. The difference between the [[heading]] and the [[desired track]] is the [[drift angle]]. Remember that heading is where the nose of the aircraft is pointing. So, when the nose of the aircraft is not pointing in the direction of travel, the aircraft is drifting by a certain angle. This angle is also known as the wind correction angle. ##### Track angle error The difference between the [[desired track]] and the [[actual track]] is the [[Track Angle Error]]. ##### Cross Track The distance of the aircraft from the desired track is the [[Cross Track]]. The graphic clearly show two scenarios. In the first, an aircraft is pushed by the wind, but makes no correction. We see that the [[actual track]] and the [[desired track]] are not the same, resulting in a [[Track Angle Error]]. The aircraft is pointed where it wants to go, but it will not get there. The farther the aircraft flies, the greater the cross track, meaning, the farther away it is from the desired track. However, when the pilot drifts the aircraft, we get a different result. Because the pilot adopted a drift angle turned into the wind, there is no more track angle error and the cross track is zero. The actual track and the desired track are the same, and so the pilot will arrive where he intended. ## Conclusion Two fairly different topics, superheterodyning and navigation basics. But, as explained, these are all part of understanding avionics systems. Radio has been for a long time the main technology that has made aircraft navigation possible. Get going on the Mandatory Project, and don't forget to use the weekly practice quiz in eCentennial to make sure you are up on all of the material from this week. You will be tested on this in week 3, and then again in week 4 on the midterm, and on the final. 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