RADIO MECHANICS

Example 1EP = 220 voltsES = 50 voltsNP = 1,500 turnsNS = ?Applying the formula : EP= NP ES = NS 220 = 1,500 turns (by cross multiplication) 50 V NS 220 V x NS = 50 V x 1,500 T ( by transposition) NS = 50 V x 1,500 turns 220 V = 75,000 220 NS = 340.90 turnsVoltage Ratio The ratio of the primary voltage to the secondary (induced) voltage is equal to the ratio between thenumber of primary and secondary turns. This relationship is expressed in this formula: EP = NP ES NS The foregoing formula shows that voltage ratio can be varied by changing the ratio between the pri-mary and secondary turns. If primary winding has more turns that the secondary winding, the voltage is re-duced. If the primary winding has less turns than the secondary, voltage is increased.Example 2 A transformer operated from a 220-volt source has a primary winding of 500 turns and a secondarywinding of 200 turns. What will be the secondary voltage? 19

Applying the formula: EP = NP ES NS 220 V = 500 turns ES 100 turns 500 x ES = 220 V x 100 turns ES = 220 V x 100 turns 500 = 22,000 500 ES = 44 voltsCurrent Ratio A step-up transformer may produce more voltage at its seconday than what is applied across its pri-mary winding. However, the secondary current will have to be proportionally less than the primary current.Secondary current is inversely proportional to the turns ratio. This can be expressed in the following formula: NP = IS NS IPExample 3 A power transformer has a primary winding of 150 turns and a secondary of 800 turns. If the currentat the primary winding is 2 amperes, how much is the secondary current?Given : NP = 150 turns NS = 800 turns IP = 2 A IS = ?Applying the formula: NP = IS NS IP 150 turns = IS(by cross multiplication) 800 turns 2A IS x 800 turns = 2 A x 150 turns 20

IS = 2 A x 150 turns 800 turns = 300 800 IS = 0.375 ASelf-checkAnswer the following questions:1. What formula is used to express the turns ratio of a transformer? voltage ratio of transformer? current ratio of transformer?2. What are the basic parts of a transformer?Activity 4 Solve for the unknown data in the given sets of transformer ratio and proportion.1. NP = 5,000 turns NS = 1,000 turns IS = 3 amperes IP = ?2. EP = 220 volts ES = 50 volts NS = 300 turns NP = ?LET’S SUMMARIZE • Resistors can be connected in series-parallel and series-parallel combinations. • In series connections, there is only one path for current to flow in and voltage supply is divided among the connected resistors. • In parallel connections, voltage source is common to all connected components. Current has two or more paths to flow in and the total resistance becomes lower than the lowest resistance value connected. 21

• In series-parallel connections, current divides in the parallel path and comes together in the series portion. • Capacitors can also be connected in series and parallel. • Connecting capacitors in series means decreasing the total capacitance, while connecting them in parallel means increasing total capacitance. • Like resistors and capacitors, inductors can also be connected in series and parallel. Connecting inductors in series, increases inductance, connecting them in parallel, decreases inductance.POSTTESTDirections: Read each statement carefully. Place a check mark on the blank before the number if the statementis correct; a cross, if wrong. __ 1. Each resistor in a series circuit serves as a voltage divider. __ 2. Only three resistors can be connected in parallel. __ 3. If three 20-ohm resistors are connected in series, total resistance will be 60 ohms. __ 4. If five resistors are connected in series, current at R1 is the same at R5. __ 5. Current has only one path to flow in parallel-connected resistors. __ 6. Each resistor acts as current divider if connected in parallel. __ 7. If one of the resistors connected in series becomes defective, it affects the whole circuit. __ 8. Total resistance grows higher when resistors are connected in parallel. __ 9. Voltage drop across each resistor adds when they are connected in series. __ 10. Current is the same in all points of series-connected resistors. __ 11. The secondary current in a transformer is inversely proportional to the turns ratio. __ 12. More turns of wire in the secondary means a higher secondary voltage. __ 13. Parallel inductors provide higher inductance. __ 14. Total inductance increases when mutual inductance between two coils is series-aiding. __ 15. A step-up transformer produces more secondary voltage than what is applied across its primary winding. ___ 16. The secondary voltage of a transformer is reduced when the primary winding has more turns than the secondary. ___ 17. Connecting inductors in series means a higher inductance. ___ 18. Capacitance values of capacitors rise when they are connected in parallel. ___ 19. Connecting capacitors in series means increasing capacitance. ___ 20. Working voltage of capacitors add when they are connected in series. 22

KEY TO ANSWERS Posttest 1. 9Pretest 2. 81. on 3. 92. on 4. 93. off 5. 84. on 6. 95. on 7. 96. off 8. 87. on 9. 98. on 10. 99. off 11. 910. on 12. 911. off 13. 812. on 14. 913. on 15. 914. on 16. 915. on 17. 916. on 18. 917. off 19. 818. off 20. 919. on20. on 23

Module 6 Fourth Year Powerful Energizers (Low Voltage Power Supplies)What this module is about Projects and activities make the difference in technical training. There is no easier, taster and morepractical way of learning electronics than through kits or projects. Today, there are many interesting kits orprojects you can assemble while learning the technical skills you need to start a chosen career. Through simplecircuits and projects in this lesson, you can develop your skills by yourself. Theory alone, may be all that anengineer needs, but it is enough for a technician. What is important is how theory is put into practice, and howelectronics really works. Moreover, the usual troubles in low voltage supply are explained, including the prac-tical methods in troubleshooting or repairing work. Upon completion of this module, you should have been able to do the following:1. Cite the different types of low voltage power supply.2. Identify the basic parts of a power supply.3. Draw the schematic diagram of different low voltage power supplies.How to learn from this module Following are tips on how to use this module. This will guide you in learning the different lessons. Youwill find this module very helpful as you read through.1. Read the objectives for you to know what you expect to learn from this module.2. Be sure to work on each activity because each one prepares you for the next.3. Answer the pretest before you go over the module to determine what you already know about the topics. Use the key to correction at the back to check your answer, but do this only after completing the module. Always answer the self-check after each activity to determine whether you understood what you are expected to do.4. Read the lessons again if you were not able to answer the questions correctly. 1

Before you go through this module, try to answer the pretest. This will help you find out what youalready know and what you still need to know about power supply. Good luck!PRETESTDirections: Read each statement carefully and place the letter of the best answer on the blank before eachnumber. ____ 1. Adevice used to convert high voltage to low voltage. a. junction diode b. transformer c. zener diode d. fuse ____ 2. A component used to convert AC to DC. a. switch b. plug c. rectifier diode d. zener diode ____ 3. For better filtering action in power supply, what do we normally use? a. resistor b. ceramic capacitor c. electrolytic capacitor d. mylar capacitor ____ 4. Used as a circuit protector in any electronic equipment. a. switch b. coil c. bulb d. fuse ____ 5. Which is normally higher in voltage in power supply? a. secondary voltage b. primary voltage c. DC voltage d. Output voltage 2

____ 6. Power supply that uses one diode as rectifier. a. half-wave rectifier b. full-wave rectifier c. bridge-type rectifier d. voltage doubler ____ 7. The rectifier that produces higher percentage of current. a. half-wave rectifier b. bridge-type rectifier c. full-wave rectifier d. voltage doubler ____ 8. The power supply that uses four diodes. a. bridge-type rectifier b. half-wave rectifier c. converter d. full-wave rectifier ____ 9. The normal frequency used in an AC input. a. 50 hertz b. 120 hertz c. 60 hertz d. 40 hertz ____ 10. Insufficient filtering of this kind of voltage can cause hum in a radio or television receiver. a. AC ripple voltage b. direct current c. alternating current d. pulsating DC Did you fare well? If not, don’t worry. Anyway you will be answering the same set of test after youhave studied all the lessons in this module. By that time, you shall have been able to answer all the questionscorrectly. Take note, if you need any resistance in carrying out the different activities, don’t hesitate to ask the helpof your teacher. For enrichment, read more about the topics from books which you will borrow from your school orany public library. 3

Lesson 1 Types of Low Voltage Power Supply Insufficient filtering of theAC ripple voltage can cause hum in radio or televesion receiver. The prob-able cause of this trouble is the open or leaky filter capacitor. With anAC input of 60 hertz, the hum frequencyfor a half-wave rectifier is 60 herts, and the ripple frequency for full-wave rectifier is 120hz. The following typesof rectifier circuits are frequently used for a DC rectified power supply operating from 100V or 220V 60hz ACpower line.Types of Low Voltage Power Supply1. Half-wave rectifier power supply - This is simple and economical power supply circuit which was only one diode. Ripple frequency is 60 hertz.2. Full wave (center-tap) rectifier -A device which rectifies both half-cycles of anAC voltage to produce DC voltage. Two diodes can produce double the load current. Ripple frequency is 120 hertz.3. Full wave (bridge-type) rectifier - Four diodes are interconnected for fullwaveAC rectification without a center tap inAC output. Ripple frequency is 120 hertz.Schematic Diagram z T IN40016 + 50 VDC 66 SW X 6 z 50 VDC +-dF 7A 1000 9470 Ω 0 uf / 25 V z -Schematic Diagram of Full-wave Rectifier - Two Diodes T IN4001 x 2 z 6 D1 + ++z 50 VDC 0 SW z 50 VDC - 9470 Ω +- X D2 z-dF 1A 1000 220 VAC uf / 25 V z 4

Schematic Diagram of a Bridge-type Rectifier (full wave with four diodes) IN4001 x 2 D1 to D4 T 66 + 6 z z SW 6 + 50 VDC X 10009- 50 VDCdF 1A uf / 25 V +- 0 470 Ω 220 VAC z-Activity 1 Draw the schematic diagram of the following power supply on an illustration board - half wave rectifier,full wave rectifier, and bridge-type rectifier.Materials Needed1 transformer 220 V primary 6V or 6V secondary7 diodes IN40013 capacitors 1000 uf/25V3 470 Ω 1/2 W3 line cords with plug3 switches - spst3 fuse holder IA small3 fuse IA small1 illustration board size 1/85 meters stranded wire red5 meters stranded wire blackProcedure:1. Draw the schematic diagram of the different power suppliers.2. Labe each part, indicating the corresponding value.3. Mount the different components on top of the components drawn on the illustration board.4. Connect the leads of the different components using stranded wire, red for the positive side and black for the negative side of the power.5. After connecting the wires at the illustration board, measure the output voltage of the half-wave rectifier, full wave rectifier and bridge type rectifier to determine if you succeeded in performing the activity by means of 5

the voltmeter, as shown in Figure 1, Figure 2 and Figure 3. Be sure to set your voltmeter to 50 VDC.Record results on Table 1. Table 1Power Supply Output Voltage in DCHalf -wave rectifierFull-wave rectifierBridge-type rectifierSelf-check1. What is the difference between a half wave and a full wave rectifier?2. What component is normally used as a filtering device?3. What is the main use of a transformer? diode? fuse? switch? electrolytic capacitor?4. What is the difference between the AC and DC voltages?LET’S SUMMARIZE Low voltage power supply consists of the transformer, the rectifier, filter capacitor, and resistor andalso the switch, fuse and the cord with its plug. When a power supply is operating into a load, it produces anoutput voltage. If the load is completely removed from the supply, the output voltage eventually increases.Usually, poor filtering action is the undesirable result of an open filter capacitor. With an open fuse, or diode ina half wave rectifier circuit, an open filter or resistor where there is no BT voltage. Acommon cause of reducedBT voltage and excessive hum is an open input filter capacitor.POSTTESTDirections: Read each statement carefully and place the letter of the best answer on the blank before eachnumber. ____ 1. Adevice used to convert high voltage to low voltage. a. junction diode b. transformer c. zener diode d. fuse 6

____ 2. A component used to convert AC to DC. a. switch b. plug c. rectifier diode d. zener diode____ 3. For better filtering action in power supply, what do we normally use? a. resistor b. ceramic capacitor c. electrolytic capacitor d. mylar capacitor____ 4. Used as a circuit protector in any electronic equipment. a. switch b. coil c. bulb d. fuse____ 5. Which is normally higher in voltage in power supply? a. secondary voltage b. primary voltage c. DC voltage d. Output voltage____ 6. Power supply that uses one diode as rectifier. a. half wave rectifier b. full wave rectifier c. bridge type rectifier d. voltage doubler____ 7. The rectifier that produces higher percentage of current. a. half-wave rectifier b. bridge-type rectifier c. full-wave rectifier d. voltage doubler____ 8. The power supply that uses four diodes. a. bridge type rectifier b. half wave rectifier c. converter 7

d. full wave rectifier ____ 9. The normal frequency used in an AC input. a. 50 hertz b. 120 hertz c. 60 hertz d. 40 hertz ____ 10. Insufficient filtering of this kind of voltage can cause hum in a radio or television receiver. a. AC ripple voltage b. direct current c. alternating current d. pulsating DCKEY TO CORRECTION1. b2. c3. c4. d5. b6. a7. b8. a9. c10. a 8

Radio Mechanics Fourth Year Module 7 The Building Blocks Stages of AM Radio ReceiverWhat this module is all about Undoubtedly, the superheterodyne principle reigns supreme in current receiver design. Superhetero-dyne radio receiver or “superhets” were mass produced with great success every fifty years. The superheatdesign offers the prime advantages of high selectivity and high sensitivity which remain fairly constant through-out the tuning range of a receiver. It was natural that, from the very beginning, transistor radios used thesuperheterodyne principle.At the end of this module you should have been able to:1. Identify the basic stages of AM radio receivers.2. Explain the function of each stage.How to learn from this module Following are some tips on how to use this module. These will guide you in working out the activitiesand summarizing what you have learned.1. Read the objectives so you will know what you expect to learn from this module.2. Be sure to work out each activity because each activity prepares you for the next.3. Answer the pretest before you go through the module to determine what you already know about the topics. Use the key to correction to check your answers but do this only after completion of the module. Always do the self-check after each activity to determine whether you understood what you have read.4. Read the lessons again if you were not able to answer the questions correctly. Before going through this module, try to answer the pretest. This will enable you to find out what youalready know and what you still need to know about AM-Radio Receivers. Good Luck! 1

PRETESTDirections: Read each statement carefully and choose the letter of the best answer.1. The modulated r-f signals, transmitted from radio stations in the area are picked up or intercepted by the a. speaker b. diode c. antenna d. IFT2. This circuit is tuned by the listener who rotates the receiver tuning dial to the desired station’s carrier frequency to accept and amplify the selected signal. a. IF amplifier b. detector c. RF amplifier d. mixer3. ______ is also tuned to accept only R-F and oscillator signals. a. oscillator b. mixer c. signal d. AGC4. _____ is a generator of an unmodulated r-f signal at a frequency of about 455 KHZ, above the desired incoming r-f signals frequency. a. mixer b. oscillator c. AFC d. AGC5. _____is fixed-tuned to accept and amplify only the 455 KHZ difference signal ( the intermediate frequency) a. IF amplifier b. Audio amplifier c. AGC d. detector6. _____removes the audio component from the i-f signal and transfers it to the audio driver stage. a. AGC b. AFC c. oscillator d. detector stage 2

7. The gain of this stage may be controlled automatically by the ______circuit to compensate for variations in signal strength. a. automatic gain control b. automatic frequency control c. oscillator d. mixer8. The normal frequency use for the IF stage a. 50 hz b. 120 hz c. 455 khz d. 60 hz9. The IF stage of anAM receiver uses_____number of IFT (intermediate frequency transformer) a. 4 b. 3 c. 2 d. 110. The AM tuner stage normally uses _____transistors specially in 7 transistorAM radios. a. 5 b. 4 c. 3 d. 2 How did you fare? If not, don’t worry. Anyway you will take the same test after you have studied allthe lessons in this module. By that time you shall have been able to answer all the questions correctly. If you need any assistance in carrying out the different activities, don’t hesitate to ask the help of yourteacher. 3

Lesson 1 Basic Stages of the AM-Radio ReceiverAntennaR-F R-F I-F I-F A-F A-F A-F9 Speaker 9R-F AMPMixer I-F AMP Detector Audio Audio 9 Driver Output 9 9 AGC R-F Oscillator Battery Block Diagram of a TypicalAM Superheterodyne Receiver Signals at Various Points in the Receiver. This is a block diagram of a typical amplitude-modulated (AM) superheterodyne broadcast band receiver.Each block represents a stage. In some receivers, some of the stages shown are omitted or additional stagesadded, according to the requirements of the particular receiver design. Activities in the operation of the receiver are as follows: The modulated r-f signals, transmitted from radio stations in the areas are picked up or intercepted by theantenna and fed to the first stage - the r-f amplifier. This circuit is tuned by the listener who rotates thereceiver’s tuning dial to the desired station’s carrier frequency to accept and amplify the selected signal. In thestandard broadcast band, there will be a frequency between 530 khz to 1600 khz. After the modulated r-fsignal is selected and amplified, it is fed to the mixer stage. The r-f amplifier has thus provided a certain extentof selectivity and sensitivity that is required. This stage is omitted. The mixer and oscillator stages perform the actual superheterodyne function. The oscillator stage is agenerator of unmodulated r-f signals at a frequency of about 455 khz above the desired incoming r-f signalsfrequency. The oscillator stage is tuned simultaneously (ganged) with the r-f amplifier stage in order that ther-f amplifier is tuned from one frequency to another, the oscillator is tuned to a frequency precisely 455 khzabove the radio frequency. Both the r-f and oscillator signals are fed to the mixer. The mixer is also tuned to accept only the r-f and oscillator signals. In this stage, the two signals are 4

heterodyne (beat together) to produce new signals. The output of the mixer stage consists of the incoming r-f signal, the oscillator signal, and two new signals - the sum and difference of the two input signals. As thereceiver is tuned throughout the band, one of these frequency signals remains constant. This is the differencesignal, which is always 455 khz and contains the same audio modulation as the original r-f signal at the antenna.This signal is fed to the i-f amplifier stage. The i-f amplifier is fixed to accept and amplify only the 455 khz difference signal (called the intermediatefrequency). The gain provided by this stage remains constant over the entire broadcast band and provides highgain since amplification of a lower frequency signal is being performed. The gain of this stage may becontrolled automatically by an AGC (automatic gain control) circuit to compensate for variations in signalstrength. The i-f signal is then fed to the detector stage. The detector stage removes the audio component from the i-f signal and transfers this to the audio driverstage. The signal is recovered by rectifying and filtering the modulated i-f signal. The detector is also the sourceof AGC voltage. The audio driver stage amplifies the audio signal and feeds it to the audio output stage. The audiooutput stage further amplifies the audio signal thus developing sufficient power to drive the speaker. The soundwaves produced by the speaker are the same sound waves which are used to modulate the r-f carrier at theradio station’s transmitter. Power for the transistors to accomplish its diverse functions is most often supplied by a battery. Batterypower is supplied to all stages except the detector when a diode rectifier is used. Figure 2 Schematic Diagram of anAM Receiver 5

Figure 3 Block Diagram of an AM Radio Tuner Figure 4 Schematic Diagram of the Radio TunerFigure 5 Test results show that resistance of the coil is higher. 6

Figure 6 Test results show that resistance of the coil is lower. Figure 7 Schematic circuit showing the connection of the antenna.Figure 8 Schematic circuit showing the connection of the tuning capacitor to the antenna and local oscillator. 7

Figure 9 Schematic circuit showing the connection of the mixer-converter transistor.Figure10 Schematic circuit showing the connection of the tuning capacitor at the antenna and the local oscillator.Figure 11Actual appearance of Figure 12 Actual appearance of the first IFT showingthe first IFT with its metal shield. the primary and secondary windings, without the metal shield. 8

Figure13 Schematic symbol of the tuning Figure 14 Pictorial appearance of the tuning capacitor. capacitor.Figure 15 Schematic circuit showing the connection of the 1st IFT.Figure16 IF signal is converted by the detector to audio signal. 9

Figure17 Schematic diagram showing the connection of the first intermediate frequency amplifier transistor. Power Output Speaker Volume Control Volume Amplifier Driver Sections AmplifierInputPower SupplyFigure 18 Block diagram of the amplifier.Figure 19 Schematic diagram of the amplifier. 10

Figure 20 Circuit connection and parts of the driver transistor. Figure 21 Schematic circuit of the power output amplifier section.Activity 1 Assembling the AM Radio Receiver You will assemble an AM radio receiver based on the kit model available at the market.Materials Needed Buy : 1 - CMC kit - 7 transistor radio Borrow from your teacher the following tools and instruments: 1 - soldering iron - 30 watts - 220VAC 1 - long nose plier 1 - diagonal cutter 1 - screwdriver (standard) small 1 - Phillip’s screwdriver 1 - V.O.M. 11

Procedure: 1. Count the number of components you bought from the electronics store. List of components are listed down on the schematic diagram given to you. Check the pictorial diagram, too. 2. Test all components, using V.O.M. to determine if it is good or bad. Use the testing procedure you learned in Module 4. 3. Check and give the color code of all the resistors to be used in assembling your AM radio receiver. 4. Check also the value of capacitors, diodes, and transistors given to you. 5. If everything is ready, start mounting all the resistors, followed by ceramic capacitors, electrolytic capacitors, transistors, diode, IFT, volume control, antenna coil, antenna holder, connecting wires, black for negative and red for positive. 6. Follow the correct procedure of mounting components as illustrated in Figure 1. Capacitor Transistor Capacitor Resistor + - ECB CeramicsResistor Transistor +- Ceramics ECBClearance + - ECB + - ECB Not This This Figure 22 Positioning of Components7. Observe correct polarity of electrolytic capacitors, correct basing of transistor leads, the emitter must be mounted to letter E, collector to letter C, base to letter B. Ceramic capacitors have no polarity or negative (-) or positive (+) signs, so you can invert the lead of ceramic capacitors.8. If everything is mounted properly then you can now start soldering the components. Follow the correct soldering procedure as illustrated in Module 2 - Soldering Techniques.9. Cut all the excess wires or leads after soldering the components. Use the diagonal cutter in cutting excess leads.10. Observe the correct positioning of the antenna coil specially the connection of primary and secondary windings. Refer to the pictorial and schematic diagram given to you.11. After soldering all the components, connect the speaker (4 inches, 8 Ω, 2 watts) and the 6-volt battery. Observe the correct polarity of batteries- negative to the black wire and positive to the red wire.12. Turn on the switch of the volume control and start testing your radio receiver. If any problem arises, refer to Module 8 for troubleshooting techniques. 12

Self-check:1. What is the meaning of AM?2. Give the main function of the antenna.3. What component is usually used as detector?4. What stage of the AM receiver provides radio station from 530 khz to 1600 khz?5. Name the stage that provides audio or sound in a radio receiver.Activity 2 AM Tuner AlignmentMaterials Needed 1 - AM radio receiver --Assembled with 3 or more stations 1 - screwdriver (standard) small -- if possible with a plastic endProcedure A. IFT Adjustment Procedure 1. Turn the radio to ON with 50% sound. 2. Turn the tuner slowly from right to left and stop at a weak station. 3. Tune the tuning capacitor to 1600 khz, or to the highest station in your area. 4. At this point, adjust IFT black slowly back and forth until the maximum signal is achieved. 5. Follow the same procedure with IFT white and IFT yellow for maximum volume. B. TrackingAlignment 1. Set the pointer of the dial to the station with the lowest frequency (M. Mla. Area - 558 khz - RMN). Adjust the antenna coil back and forth for maximum signal. 2. Turn the pointer of the dial to the station with the highest frequency (M. Mla.Area - 1570 khz DZHH). Adjust the oscillator trimmer (o) to obtain the station, then adjust the antenna trimmer (a) to achieve maximum signals. Use a small standard screwdriver in adjusting, the IFT, Red Oscillator, antenna trimmer, and oscillator trimmer. 3. Return to the station with the lowest frequency, following the same procedure as B-1, then back to the station with the highest frequency using the same procedure in No. B-2. Repeat procedures B-1 and B-2 at least twice. The alignment is now complete. 13

Antenna Coil Primary Coil Secondary Or Antenna Bar Coil Volume ControlFerrite Core Oscillator trimmer Antenna trimmer Tuning Capacitor Red 1st IFT 2nd IFT 3rd IFT Oscillator Yellow White Black Pictorial view of the most important components in the alignment of theAM tuner-radio receiver.Self-check:1. What is the frequency of the RMN station?2. The color of oscillator coil is ______.3. The frequency of the DZHH station is ______.4. To achieve 1570 khz DZHH, adjust ______ for maximum signal.5. To achieve 558 khz RMN, adjust ______ for maximum signal.LET’S SUMMARIZE This module is all about the operation of radio receivers and the function of each block. It also takes up theprinciple of modulation in radio broadcasting and reception. In this module, students experience basic RFcommunications, using theAM radio receiver as medium. The module also includes discussion on adjustmentsand signal orientation. Assembling of anAM receiver is also one of the activities. Standard radio broadcaststations use amplitude modulation (AM) to transmit audio signals or information (voice and music) in the radiofrequency (RF) carrier wave. Amplitude modulation also involved mixingAF and RF signals, although this timeand the amplitude of the carrier is altered. The mixing of these signals is similar to the heterodyning process. 14