AMATEUR BASIC LICENCE COURSE - LESSON OUTLINE - MAR 1998 Numbers in [ ] are chapters from the RAC study guide. Items marked * are extra material, not on the exam. Each numbered item should take approximately 15 minutes to present. Each session is 3 hours (12 items, including a 15 minute break.) E. WEEK 3 - MORNING - Antennas INSTRUCTOR: Grant VE3GCQ EQUIPMENT: antenna tuner, SWR meter 1. Homework review 2. MORSE LESSON 5: ZVXJ Words JAZZ VEX ZOOM JUST SIX VOW 3. Transmission Lines [7] a) You need two wires to connect a battery to a load. Likewise, you need two conductors to connect a transmitter to an antenna. b) This is called a "transmission line": two conductors designed to carry RF energy efficiently. There are two types. c) BALANCED or "parallel" transmission line has two identical wires side by side, with nothing around them. They have some insulator between them to keep them evenly spaced. (SHOW EXAMPLE OF TWIN-LEAD) d) Balanced lines are not shielded, and must be kept away from other conductors like metal towers or the ground. e) UNBALANCED or "coaxial" transmission line has one conductor inside the other. The inner conductor is a wire, the outer conductor is a hollow tube. This tube can be solid copper or braided wire. (SHOW EXAMPLES OF COAX). f) The outer conductor is a shield -- all RF energy stays within it. Coaxial cable can be freely placed near metal or even buried, which is why it is commonly used. g) All transmission lines have a CHARACTERISTIC IMPEDANCE. If you were to connect a battery to an infinitely long line, it will accept current only at a certain rate. It looks like a resistor. h) The characteristic impedance is measured in ohms. It is determined by physical diameter and spacing of the conductors, and the dielectric material (insulator) between them. i) TV "twin-lead" has a characteristic impedance of 300 ohms. j) Coaxial cable used for television has a characteristic impedance of 75 ohms. k) Coaxial cable used for most amateur, CB, and commercial radio has a characteristic impedance of about 50 ohms. l) The characteristic impedance is NOT affected by the length of the line. For example, a piece of RG-213 cable has a characteristic impedance of 50 ohms, whether it's 1 foot long or 100 feet long. m) PRACTICE QUESTIONS: 2-118, 2-083, 2-082, 2-014. 4. Impedance Matching [7] a) Every antenna has a natural impedance. Transmitters are designed to drive a certain impedance (usually 50 ohms). For optimum power transfer, the antenna impedance must match the transmitter, and the line impedance must match both. b) It's easy to make the line impedance match the transmitter -- just buy the right cable. (50 ohm cable for amateur use.) c) The problem is making the antenna match. If the antenna impedance is different from the line, power is reflected back from the antenna. This causes power to be lost (turned to heat) in the transmission line. d) If the antenna impedance doesn't match the transmitter, the transmitter can overheat or be damaged. e) The ideal is to "terminate the transmission line in its characteristic impedance", that is, make the antenna match the line perfectly. Then all power is absorbed by the load (the antenna). f) A perfect match looks exactly like an infinitely long transmssion line. g) One way to match the antenna is with a transformer. These often match balanced antennas to unbalanced transmission line, and so are called "baluns" (for BALanced/UNbalanced). For example, you can buy a commercial balun to give a 4:1 impedance ratio (it will match 200 ohms to a 50 ohm line). h) Another way to match impedances is with an "antenna tuner", also called a "match box" or "transmatch". (SHOW TUNER) This can prevent a transmitter mismatch (and thus prevent transmitter damage). But it does not match the line to the antenna, so power is still lost. i) PRACTICE QUESTIONS: 2-081 (DISCUSS), 2-086, 2-121. 5. Standing Wave Ratio (SWR) [7] a) When the line doesn't match the antenna, power is reflected. This combines with the outgoing or "forward" power to cause STANDING WAVES on the line. b) Standing waves are measured by Standing Wave Ratio, or SWR. A standing wave ratio of 1:1 is a perfect match. c) As the mismatch gets worse, the standing wave ratio goes up. Most transmitters can tolerate an SWR up to 2:1. d) The worst possible match is a short circuit or an open circuit (no antenna connected). In either of these cases, the SWR becomes infinite. e) Standing wave ratio is measured by an SWR meter. 1) The SWR meter reads forward and reflected power (or sometimes forward and reflected voltage). (SHOW METER) 2) Most meters have a single meter and a switch. You set the meter to read full scale in the "forward" position. Then you switch to the reverse position, and the meter indicates SWR directly. f) PRACTICE QUESTIONS: 2-089, 2-090, 2-109. 6. Half-wave dipole [8] a) The most basic antenna is a half-wave dipole. b) A wire one-half wavelength long will resonate, like a guitar string. When it resonates it transmits and receives radio waves most efficiently. c) For example, at 1 MHz the wavelength is 300 metres. Therefore a dipole for 1 MHz would be 150 metres long, half a wavelength. d) Remember that shorter wavelengths correspond to higher frequencies. So if you shorten a dipole, you make it resonate at a higher frequency. e) If you were to measure the AC CURRENT in the antenna, you would find the maximum amplitude at the CENTER of the antenna. You would find no current at the ends. (SHOW DIAGRAM) f) If you were to measure the AC VOLTAGE on the antenna, you would find the maximum amplitude at the ENDS of the antenna. You would find no voltage at the center. g) For most dipoles, the transmission line is connected at the center. This is the place of maximum current. This is called "center feed". h) A center-fed dipole has an impedance of about 73 ohms. This is a good match to 75-ohm cable. i) There is a variant called a folded dipole which has a feed point impedance of about 300 ohms. (SHOW ILLUSTRATION) j) Most of the RF energy is radiated broadside from a dipole. No energy is radiated from the ends (i.e., along the length of the dipole). (SHOW DIAGRAM) k) The angle of radiation up from the horizon is determined by how high the antenna is above ground. For best results, mount dipoles at least 1/4 wavelength above ground. l) Dipoles also work on odd multiples ("harmonics") of the resonant frequency. For example, a 1 MHz dipole will also work for 3, 5, 7 MHz and so on. m) PRACTICE QUESTIONS: 2-008, 2-095, 2-015, 2-093. 7. BREAK 8. REGS: Power Limits a) The maximum power you can use depends on the operating mode. b) For most modes, you can measure the DC power supplied to the final amplifier. This "DC input power" can be up to 250 watts. c) Or, you can measure the actual RF output power from the transmitter. This "carrier output power" can be up to 190 watts. d) Single-sideband transmitters are measured in terms of "Peak Envelope Power", also called "PEP output power". This can be up to 560 watts. Since this is hard to measure, for practical purposes you should buy a transmitter that is rated lower than this. e) Basic: 250 W DC input, 560 W PEP output, 190 W carrier out f) If you have ADVANCED qualification, these limits go up to: 1000 watts DC input power 750 watts carrier output power 2250 watts PEP output power (for SSB transmitters) g) You cannot own a transmitter capable of producing more than twice your authorized power, even if you turn it down. On the exam, this is stated "more than 3 decibels" over your authorized power. (We'll learn about decibels later.) h) For "radiotelephony" (voice) you must not use more than 100% modulation. Your transmitter must either have a modulation indicator, or an "ALC" circuit which automatically limits the modulation to a legal value. i) You must have a way to "determine" your transmitting frequency. For most transmitters, this is the tuning dial. j) When operating below 148 MHz, your transmitter's frequency must be a stable as "crystal control." All modern manufactured transmitters meet this requirement. k) PRACTICE QUESTIONS: 3-021, 3-017, 3-024. 9. Vertical Antennas a) If you take half of a dipole antenna and mount it vertically over ground, you get a "quarter-wave vertical" antenna. b) The electrical behavior of the ground can be simulated by a "ground plane", thus known as a "ground plane" antenna. The ground plane can be horizontal wires or flat metal (such as the roof of your car). c) This antenna is OMNIDIRECTIONAL, which means it radiates equally well in all directions. d) The feed point impedance of the 1/4 wave antenna is about 50 ohms, which is a good match to 50-ohm coaxial cable. e) You can also make a vertical antenna which is 5/8 of a wavelength long, thus called a "5/8-wave vertical". Its main advantage is a lower angle of radiation, which gives better range. f) You can make an antenna physically shorter without changing its resonant frequency, by adding LOADING COILS. These are just inductors (coils) in series with the antenna wire. g) A series inductance makes the antenna element look electrically longer. h) This is used to make short antennas. i) PRACTICE QUESTIONS: 2-018, 2-101, 2-114, 2-040. 10. Yagi antenna [8] a) The Yagi-Uda antenna, or simply Yagi, is a DIRECTIONAL antenna named after its inventors. b) "Directional" means it concentrates radio energy in one direction, and it is most sensitive in that direction. c) It consists of a dipole, a REFLECTOR, and one or more DIRECTORS. (SHOW BLOCK DIAGRAM) d) The reflector is slightly longer than the dipole, and is mounted "behind" the dipole. It tends to reflect radio energy back the other way (hence the name). e) The directors are slightly shorter than the dipole, and is mounted "in front" of the dipole. Directors tend to focus the radio energy. f) The reflector and directors are just wires, not connected to anything. They work by picking up RF radiated by the dipole. So they are called "parasitic" elements. The antenna is sometimes called a "parasitic array". g) Since the dipole is the only thing connected to the transmitter, it is called the "driven element." h) PRACTICE QUESTIONS: 2-110, 2-111, 2-011. 11. Antenna specs: gain and bandwidth a) The Yagi concentrates the RF energy in one direction. So, 10 watts into a Yagi may deliver as much signal to the far end as 20 watts into a dipole. b) In this case, we would say the Yagi has a "two times" power gain over the dipole. c) Except we don't say "two times" or "ten times". We measure power gain in DECIBELS. d) Decibels indicate a power ratio. The two easiest ones to remember are: 3 decibels = two times the power 10 decibels = ten times the power e) So if a Yagi has 10 decibels gain over a dipole, it appears to put out 10 times as much power. 10 watts into this antenna would be as effective as 100 watts into a dipole. f) You're not really radiating more power, you're just focusing it in one direction. So this doesn't affect your legal limits. g) Sometimes you'll hear about decibels over an ISOTROPIC antenna. This is a hypothetical "point source" antenna which radiates uniformly in all directions. So it's even less focused than a dipole. h) You'll also hear about antenna BANDWIDTH. This is the range of frequencies for which the antenna will give an acceptable SWR (typically 2:1). i) For testing transmitters, we use a "dummy load". This is a device which looks like an antenna, but doesn't radiate any RF signal. j) PRACTICE QUESTIONS: 2-113, 2-106. 12. Polarization [8] a) Remember that a radio wave has an electric "E" field, and a magnetic "M" field, at right angles. So if one is oscillating vertically, the other is oscillating horizontally. b) We call the direction of the electric field the POLARIZATION of the radio wave. c) Two radio stations must use the same polarization in order to communicate. d) This is most important for line-of-sight communications, such as VHF radio. For instance, all 2m FM communications is done with vertical polarization. e) This is less important for skywave communications on HF, because reflection from the ionosphere will change the polarization of the signal. f) PRACTICE QUESTIONS: 2-007, 2-116. 13. MORSE REVIEW 5: ZVXJ Words VIEW BOX JUNK FIZZ UVULA JOG ZING XEROX JAZZ VEX ZOOM JUST SIX VOW F. WEEK 3 - AFTERNOON - The Amateur Station INSTRUCTOR: VE3XOX PROPS: SWR meter, dummy load, transmitter, antenna, power supply 1. DEMO: how to use SWR meter and dummy load a) Dummy antenna or "dummy load" is used to test or tune up transmitters, without radiating a signal. [8] 1) Connect it (with coaxial cable) to the antenna socket on your transmitter. 2) Be careful not to transmit for long periods, as the dummy load will heat up. Check the rating of the dummy load. 3) Do NOT use a light bulb. b) You know the SWR meter measures the antenna mismatch. 1) Connect it between the transmitter and the antenna. You must connect it the right way 'round. One socket will be labelled "transmitter", and the other "antenna". 2) Set up your transmitter to radiate a continuous signal (CW, or FM, or unmodulated AM). 3) CALIBRATE the SWR meter. Select "forward," transmit a signal, and turn the adjustment knob until the meter reads full scale. (If you have separate meters, set the "forward" meter to full scale.) 4) READ the SWR. Select "reverse", transmit a signal, and read the SWR off the meter scale. (If you have separate meters, read the "reverse" meter.) 5) Be sure to identify yourself after sending a test signal. E.g., "VE3RHJ testing". 2. PRACTICAL: Safety [16] (This material is also on the exam.) Amateur equipment uses potentially lethal voltages. So we have established several standard precautions to avoid shock or electrocution. a) Connect the chassis of equipment to earth ground. If the wrong wire inside the equipment shorted to the metal chassis, it could put several hundred volts on the OUTSIDE of the equipment. Connecting the chassis to ground will prevent this, and ensure that a fault will not put high voltage on the metal chassis. b) 3 wire power cords are often used to connect the chassis to ground. The third wire is the ground wire. Do NOT bypass this wire: it is an essential safety feature. c) Do NOT service equipment while it is switched on! You risk shock while the equipment is turned on. d) In fact, UNPLUG equipment before servicing it! Even when switched off, there are lethal voltages at some places inside the unit. e) If you ever come across someone who is being electrocuted, DO NOT touch him. Turn off the high voltage first! The human body is a conductor, so if you touch him, you'll get shocked too. f) PRACTICE QUESTIONS: 2-197, 1-007, 1-037. 3. MORSE LESSON 6: 12345 4. Power Supplies [10] The purpose of a power supply is to convert AC, from the wall socket, to DC at some desired voltage. On the block diagram, there are six parts: (SHOW BLOCK DIAGRAM) a) Input. This is the AC wall socket. b) Transformer. Remember that a transformer can change AC from one voltage to another. So, while we still have AC, we change the voltage to the desired value. c) Rectifier. This is a diode, which only lets current pass one way. It blocks the "wrong" half-cycle of the sine wave, thus it converts AC to pulsating DC. d) Filter. This is often a capacitor, which can store and release charge. It converts the pulsating DC to smooth DC. e) Regulator. This REGULATES the DC, that is, holds it exactly to the desired value. Even if the AC voltage changes, the DC output will remain exact. f) Output. This is the DC output to your rig. (SHOW EXAMPLE) g) PRACTICE QUESTIONS: 1-001, 1-003, 1-044, 1-046. 5. Setting up an HF Station [11] We'll first talk about what Industry Canada wants you to know about the HF station components. a) You know you need a TRANSMITTER, to generate radio signals. b) You know you need a RECEIVER, to hear the other guy's radio signals. c) You also need a TRANSMIT/RECEIVE SWITCH. This lets your transmitter and receiver share the same antenna. When you switch from receive to transmit, it must do three things: 1) Disconnect the antenna from the receiver, and connect it to the transmitter. 2) MUTE the receiver. Even with the antenna disconnected, your receiver will pick up your transmitter. This basically turns off the receiver while you're transmitting. 3) Turn on the transmitter. d) Unless you collect antiques, you'll probably buy all three of these in one package. This is called a TRANSCEIVER. (SHOW HF STATION BLOCK DIAGRAM) e) If you get your Advanced qualification, you might add a LINEAR AMPLIFIER. This increases your transmitter power. Since you don't always want to run maximum power, you'll have some arrangement to bypass the linear amplifier. (This is built into most modern "linears".) f) Next you should have a LOW-PASS FILTER. This reduces interference to TVs and radios. We'll talk about this shortly. g) You know what an SWR meter is. It's also called an SWR BRIDGE, and goes AFTER the low-pass filter. h) You'll probably want to use several of the HF bands, and thus several antennas. So you'll want an ANTENNA SWITCH to choose which antenna to use. i) For the bands ABOVE 14 MHZ, the wavelength is short enough that you can make Yagi antennas. Many of these antennas include a matching device for a 50 ohm impedance, so they can be connected directly to the transmitter. j) BELOW 14 MHZ, you'll probably make long wire or dipole antennas. Many of these will need an ANTENNA TUNER to convert their impedance to 50 ohms. (SHOW TUNER) k) Finally, your transmitter's final amplifier may need to be tuned for your output frequency. It's best to tune it into a DUMMY LOAD so that you don't radiate signals during tune-up. l) PRACTICE QUESTIONS: 2-171, 2-176, 2-217. 6. Setting up a 2m Station Industry Canada doesn't have any questions specifically for 2m stations. So this is for your information. a) You will need a 2m TRANSCEIVER. This can be either a handheld radio (SHOW EXAMPLE), a mobile radio designed for a car, or a base station designed for the home. b) Many people use mobile radios at home. Mobile radios run on 12 volts DC, so you need a POWER SUPPLY which plugs into the wall and produces 12 volt DC. c) You can buy LINEAR AMPLIFIERs for 2m, but you probably won't need one. d) Since the 2m transceiver works on a single band, you'll probably only need a single antenna. The most common are: 1) 1/4 wave or 5/8 wave vertical antenna. These are simple and inexpensive, and can attach magnetically on the roof of your car. For home use you'll probably need radials. 2) J-pole. This is a vertical antenna which doesn't require radials. It's good for home use. 3) Yagi. To increase your range you need a directional antenna with gain, and an antenna rotator to point it. 2m Yagis up to 11 elements are reasonably small and can be turned with a TV antenna rotator. e) You probably only need to borrow an SWR bridge when you're installing your antenna. After that, the SWR shouldn't change too much. 7. Setting up a Digital Station [11] There are three basic digital modes: packet radio, radioteletype, and AMTOR. We'll learn more about how they work when we discuss transmitters. The basic station layout is the same for all three, and this might be on the exam: a) INPUT/OUTPUT on the block diagram refers to the keyboard and screen of your computer. b) The COMPUTER converts what you type to digital signals, and displays received digital signals on the screen. c) The MODEM is the heart of the system. It converts digital signals to audio signals (sounds), which an ordinary radio can send and receive. d) For packet radio, you'll also hear the modem called a "TNC" (Terminal Node Controller). e) Packet radio uses the "ASCII" encoding for typed characters. And it adds routing and control information using the "AX.25" protocol. Remember the names. f) Finally, you have an ordinary TRANSCEIVER, g) And an ordinary ANTENNA. Nothing special here. h) PRACTICE QUESTIONS: 3-001, 3-003, 3-005. 8. BREAK 9. REGS: Operating Procedures [12] This is what Industry Canada requires you to know: a) The first rule of all amateur communication: listen before you transmit! (Yes, this is on the exam.) b) When you are talking on the radio, you must identify your station on your FIRST transmission, on your LAST transmission, and at least every 30 minutes in between. You identify by announcing your callsign by voice or morse code. c) You are NOT required to keep a logbook of all your transmissions. But many amateurs do. (SHOW LOGBOOK) It's especially nice if you want to confirm contacts with DX stations. d) You must yield the frequency for emergency transmisions. There are three levels of emergency: 1) DISTRESS. This has the highest priority. An airplane is in distress when its engine quits. 2) URGENCY. This has the second highest priority. For example, an airplane would send Urgency transmissions if it had only 15 minutes' fuel left. 3) SAFETY. This is the third highest priority. An airplane would send this if it was lost. 4) You should remember this order: first Distress, then Urgency, then Safety. e) If you hear a distress call: 1) Don't jump in; wait to see if someone else has answered it. 2) If no one has, you should render assistance. 3) This is the ONLY time you can knowingly interfere with another station. f) PRACTICE QUESTIONS: 3-013, 3-071, 3-085. 10. Radio Frequency Interference & TVI "not your transmitter" We teach you about Radio Frequency Interference and Television Interference for two reasons. First, there are a lot of RFI and TVI questions on the exam. Second, it's your responsibility as an amateur not to interfere with other services, and if you have neighbors, you may run into this someday. a) Front-End Overload This simply means that your signal is so powerful that it's overloading the receiver circuits of your neighbor's TV. It's common when you run high power on the HF bands. 1) Your transmitter is OK, so there's nothing you can fix there. 2) You need to make the TV less sensitive to your HF transmitter, without affecting its reception of VHF and UHF TV signals. You do this by adding a HIGH PASS FILTER to the TV's antenna input. This will pass the high frequencies (VHF and UHF), but block the low frequencies. b) Audio Rectification It's also possible for your powerful signal to get into the audio circuits, and get rectified (turned to audio). This is common when the speaker wires of a stereo system pick up your signal. 1) The clue: since it's overloading the AUDIO circuits, it will appear wherever the TV/radio/stereo is tuned. 2) Again, your transmitter is OK. 3) You need to prevent your neighbor's audio circuits from picking up RF. You do this by shielding his receiver, and/or by putting filters on the speaker wiring. c) Adjacent Channel interference This is like front-end overload, but occurs when your frequency is very close to the TV frequency. For example, you may be transmitting on the 50 MHz band, and your neighbor is trying to watch channel 2 at 54 MHz. 1) High-pass filters aren't good enough to separate these signals. 2) You might be able to build a BAND REJECT FILTER to block only your transmitting frequency. 3) But probably, you'll have to come to an accomodation with your neighbor. Reduce your power output, or only operate during certain hours. d) PRACTICE QUESTIONS: 2-192, 2-194, 2-195, 2-257. 11. RFI and TVI "your transmitter" a) Harmonics This is a case where your neighbor's TV is ok, but your transmitter is the problem. You're actually radiating in the television band. It happens like so: 1) If your RF isn't an absolutely perfect sine wave, it will contain HARMONICS. These are integer multiples of your base (fundamental) frequency. For example, if you're transmitting on 7 MHz, the "second harmonic" is 14 MHz, the "third harmonic" is 21 MHz, and so on. 2) This occurs when you overdrive a CW transmitter, or when you overmodulate an AM or SSB transmitter. You can fix this by reducing the drive or microphone gain. 3) You may still have weak harmonics. These can be fixed by adding a LOW PASS FILTER. A common filter will pass all frequencies below 30 MHz -- the HF amateur bands -- and block all frequencies above 30 MHz. So, any harmonics in the TV frequencies are blocked. 4) This is less of a problem with older transmitters that have "tuned" final amplifiers. Many modern transceivers require low-pass filters. Read the owner's manual. b) Spurious signals (parasitics) It's also possible for your transmitter to radiate interfering signals that are NOT harmonics. These are "spurious" signals, produced in your transmitter, amplified and transmitted. They can occur at ANY frequency. 1) A common problem is when the power amplifier becomes an oscillator. This is called "parasitic" oscillation, and is caused when there is accidental feedback or resonances in the power amplifier. 2) In the power amplifier, this is fixed by an adjustment called "neutralization." 3) Parasitics in other circuits can be fixed by shielding and filtering. c) PRACTICE QUESTIONS: 2-189, 2-209, 2-213, 2-251. 12. RFI and TVI "miscellaneous" a) Cross Modulation / Intermodulation Cross Modulation, or "Intermodulation", occurs when there are TWO (or more) strong signals on different frequencies. These signals can "mix" in a rectifier or amplifier to produce a third frequency...which just might be an interfering frequency. 1) The clue: this will appear as interference at a specific frequency. 2) You can fix this by blocking one or both of the problem frequencies. Since the problem frequencies can be above OR below the desired frequency, you use a BAND PASS FILTER. This passes a narrow band of frequencies, and blocks anything above or below. 3) If that doesn't fix it, the cross modulation may be occuring OUTSIDE the receiver. Even a corroded metal joint can pick up and mix radio signals. Your only hope is to find where this mixing occurs. b) Key Clicks This is for CW transmitters only. If you key the RF on and off instantly, you radiate a broader range of frequencies, and cause an unpleasant clicking noise in the receiver. 1) Modern transceivers are designed to turn the transmitter gradually on and off for each dit and dah. (SHOW EXAMPLES OF WAVESHAPE). 2) Older transmitters can be fixed by putting a capacitor across the key, and a choke in SERIES with the key leads. c) PRACTICE QUESTIONS: 2-256, 2-200, 2-186, 2-265. 13. MORSE REVIEW 6: 12345 G. WEEK 4 - MORNING - Transmitters INSTRUCTOR: Bernie VE3BQM 1. Homework review 2. MORSE LESSON 7: 67890 3. Amplitude Modulation [13] a) We use radio waves because they travel through the air without wires. b) But a radio wave by itself says nothing. It carries no information. To put voice, or pictures, or bits on a radio wave, we must change or "modulate" the wave in some fashion. When we do this, the radio wave is sometimes called the "carrier" (because it "carries" the information). c) The simplest modulation is simply to turn it on and off. We can send Morse code this way. This is called Continuous Wave modulation, or CW for short. d) Voice modulation is more complicated. The human voice is vibrations from 300 to 3000 Hz. A microphone converts these vibrations to alternating current. This is called the "audio" signal. A loudspeaker converts this AC back to vibrations & sound. 1) Note: a loudspeaker can also convert sound to AC, thus acting as a microphone. e) So we want to make this "audio" signal modulate a radio signal. The easist way is to make the audio voltage increase and decrease the AMPLITUDE of the radio wave. This is called Amplitude Modulation, or AM. 1) When the radio wave is "100% modulated", its amplitude is doubled when the audio signal is most positive, and its amplitude is zero when the audio signal is most negative. Increasing modulation over 100% causes distortion and "splatter". f) An unmodulated radio wave occupies exactly one frequency. A modulated radio wave occupies a narrow band of frequencies. These added frequencies are called SIDEBANDS, because they exist on either side of the "carrier" frequency. g) With AM, the AUDIO frequency determines the width of the sidebands. 1000 Hz audio causes sidebands 1000 Hz above and below the carrier frequency. Human voice (300 to 3000 Hz) causes sidebands up to 3000 Hz above and below. So the AM signal occupies a BANDWIDTH of 6000 Hz. h) All of the "information" in the signal is in the sidebands. It's possible to send only the sidebands, and not carrier frequency. This is called Double Sideband Suppressed Carrier "DSBSC", or just Double Sideband "DSB" modulation. i) Since one sideband is the mirror image of the other, it's redundant to send both. If we eliminate the carrier frequency and one sideband, what's left is called Single Sideband Suppressed Carrier "SSBSC", or just Single Sideband "SSB" modulation. 1) One big advantage of SSB is that it occupies half the bandwidth. You can have two SSB signals in the space occupied by one AM or DSB signal. j) PRACTICE QUESTIONS: 2-181, 2-178, 2-179. 4. Frequency Modulation a) You can also make the audio voltage increase and decrease the FREQUENCY of the radio wave. This is called Frequency Modulation, or FM. 1) The amount of the frequency change is called the DEVIATION. If the deviation is too large -- "overdeviating" -- the sound will be distorted in the receiver. 2) The sound can also be distored if the transmitter and receiver are not on the same frequency. b) Finally, there's a form of "on-off" frequency modulation. It's called Frequency Shift Keying or FSK. The key changes the radio wave from one frequency to another. The difference in the two frequencies is called the "shift". 1) This isn't used for Morse code. It's normally used to send bits, that is, digital computer data. 2) For digital data, the two frequencies called "mark" & "space". These correspond to the binary values 1 and 0. 3) The common digital modes are Baudot, ASCII, AMTOR, and packet. 4) Baudot is what old radioteletypes used. It uses five bits to represent a character. It is normally sent at 45.5 bits per second (baud), which yields 60 words per minute. 75 and 100 wpm are also used. The usual frequency shift is 170 Hz. 5) ASCII is what computers use. It uses eight bits to represent a character. 6) AMTOR is like radioteletype, but with error checking and automatic retransmission of lost characters. Mode B is "Broadcast" and is used to call CQ. Mode A is "Automatic Repeat Request" (ARQ) and is used after establishing contact. c) PRACTICE QUESTIONS: 2-183, 3-117, 3-006. 5. CW Transmitter [13] This is the simplest transmitter. It has six blocks. a) The POWER SUPPLY provides power to operate the transmitter. NOTE FOR THE EXAM: this is the ONLY transmitter for which the power supply is shown. b) The MASTER OSCILLATOR generates a continuous RF signal of the desired frequency. c) The DRIVER/BUFFER amplifies the signal, and isolates the master oscillator from the power amplifier. d) The POWER AMPLIFIER amplifies the signal some more, to the desired final power. e) The TELEGRAPH KEY turns the two amplifier stages on and off. This is the CW "modulation". Note that the oscillator is NOT turned on and off; it must run continuously to produce a stable frequency. f) The ANTENNA radiates the signal. Transmitters always end at the antenna. On the exam, the antenna is considered part of the transmitter (the last block.) g) PRACTICE QUESTIONS: 2-215, 2-137, 2-132, 2-134. 6. BREAK 7. REGS: Input vs Output power Look at the CW transmitter again. a) The power supply is providing DC power to the final amplifier. This is computed from the DC voltage times the DC current. This is called the "DC input" power. b) E.g. 2-270. If the "final" is taking 30 mA from a 300 V supply, the input power is 300 x .030 = 9 watts. c) The final amplifier takes this DC and converts it to radio-freqency AC power. This is what gets pumped out to the antenna. This RF power is called the "output" power. It can be calculated if we measure the RF voltage, and we know the load resistance. d) The EFFICIENCY of an amplifier is the ratio of output/input. This might range from 30 to 70 percent, depending on the design of the amplifier. e) For example, if the input power is 90 watts, and the output power is 45 watts, the efficiency is 50%. f) What happens to the "lost" power? It gets turned to heat in the final amplifier tubes or transistors. g) PRACTICE QUESTIONS: 2-271, 2-269. 8. Transmitter Building Blocks The three most important circuits in transmitters and receivers are oscillators, amplifiers, and mixers. a) An OSCILLATOR generates an AC signal. Usually this will be a radio-frequency (RF) signal. It is important that this frequency be stable; the oscillator should not "drift" in frequency. b) An AMPLIFIER makes a signal stronger. c) A MIXER changes the FREQUENCY of a signal. Actually, it takes two signals of different frequencies. The output of the mixer contains the two original frequencies, plus two new frequencies: the SUM of the original two, and the DIFFERENCE of the original two. d) For example, if you put 9 MHz and 5 MHz into a mixer, you get 9 MHz, 5 MHz, 14 MHz (the sum), and 4 MHz (the difference) at the output. e) We will see other building blocks as we look at transmitters and receivers. f) PRACTICE QUESTIONS: 2-235. 9. FM Transmitter [13] The FM transmitter is a little more complicated than the CW transmitter. It has 7 blocks. a) The MICROPHONE converts sound to electricity. This is the "audio" signal. b) Microphones produce very weak signals, so a SPEECH AMPLIFIER is used to increase the audio to a usable amplitude. c) The audio signal is then fed into a MODULATOR. This changes the frequency of the following stage, d) the OSCILLATOR. This generates the radio signal. Through the action of the modulator, the frequency of this radio signal is varied according to the audio (voice) signal. e) It's hard to make good VHF oscillators. So the oscillator works at a lower frequency, and a special circuit called the FREQUENCY MULTIPLIER increases it to the desired frequency. Frequency multipliers are simpler than mixers, but they can only produce harmonics (integer multiples) of the input frequency. f) For example, we could have a 28 MHz oscillator, and multiply it by 5 to get 140 MHz. g) Like the CW transmitter, the FM transmitter ends with a POWER AMPLIFIER and an ANTENNA. h) PRACTICE QUESTIONS: 2-216, 2-140, 2-142, 2-143. 10. SSB Transmitter [13] The most complicated transmitter is the SSB transmitter. a) Again there is a MICROPHONE, and a SPEECH AMPLIFIER. b) Again there is a RADIO FREQUENCY OSCILLATOR which produces the signal to be modulated. But now this oscillator produces a fixed and very exact frequency. And now it feeds into the modulator. c) The BALANCED MODULATOR uses an audio signal to modulate an RF signal. It produces a Double Sideband output. That is, it suppresses the carrier frequency, and lets only the two sidebands through to the output. d) The FILTER is a very narrow band-pass filter, designed to let one of the sidebands through, and block the other sidebands. Remember, the sidebands are at slightly different frequencies. e) At the output of the filter we have an SSB signal at a fixed frequency, sometimes called the "intermediate frequency." 9 MHz is a common frequency here. To convert this to an SSB signal in one of the amateur bands, we use a MIXER. f) The other input to the mixer comes from a VARIABLE FREQUENCY OSCILLATOR. Since the first input frequency is fixed, this oscillator will determine the output frequency. For example, with a 9 MHz IF, if we vary the oscillator from 5 to 5.35 MHz, the sum frequency will vary from 14 to 14.35 MHz. (This is the 20 metre ham band.) g) Finally, there is a LINEAR AMPLIFIER, and an ANTENNA. The linear amplifier is a special power amplifier that will not distort the SSB signal. h) PRACTICE QUESTIONS: 2-180, 2-123, 2-125, 2-129. 11. MORSE REVIEW 6 H. WEEK 4 - AFTERNOON - Receivers INSTRUCTOR: Bernie VE3BQM PROPS: HF rig & antenna 1. DEMO: HF phone & CW operation 2. PRACTICAL: Understanding the HF rig a) BAND SWITCH selects which HF amateur band to use. That is it selects the frequency range. b) TUNING selects the frequency within the band. c) AF GAIN is the volume control. So far these controls are similar to any AM/FM radio. Now for some new ones: d) MODE selects the type of modulation being received (and transmitted). Usually the choices are LSB, USB, CW, and (sometimes) AM. Some rigs have SB-N (normal sideband) and SB-R (reverse sideband) instead of USB and LSB. You just have to remember that below 9 MHz, "normal" is LSB. e) RF GAIN controls the sensitivity of the receiver. Normally you leave this all the way up. But if there is a strong signal overloading your receiver, you can turn this down. f) Some receivers have a PRESELECTOR to help reject signals outside the ham band. You just tune this for loudest received signal. g) OFFSET/RIT (Receiver Incremental Tuning) lets you tune the receiver to a slightly different frequency than the transmitter. This is sometimes necessary to make SSB signals sound right. It's sometimes called "clarifier". h) Some receivers let you choose different FILTERs. CW requires less bandwidth than SSB, so if you select a narrower filter, you'll hear less interference. Remember that SSB requires about 3 kHz bandwidth. CW filters are typically 500 Hz or 250 Hz. For AM you need a 6 kHz filter, and FM can require 25 kHz or more. i) Many of these controls also apply to the transmitter. Transmitters also have: j) CW DRIVE/MIC GAIN controls how strong your CW or SSB signal is. Sometimes these are two different controls, sometimes they are combined. This should always be adjusted according to the owner's manual. Turning DRIVE or MIC GAIN too high will cause distortion and interference. k) Older rigs, particularly vacuum tube rigs, have a DRIVER TUNING control. This is like a preselector for your transmitter -- you just have to tune it for strongest transmit signal. If you change frequencies, you have to re-adjust it. l) Vacuum tube rigs also have PLATE & LOAD tuning controls. These adjust a tuned circuit in the transmitter output stage. Generally you adjust the PLATE control for minimum plate current, and the LOAD control for maximum output... but follow the manufacturer's instructions. Like DRIVER TUNING, you have to readjust these if you change frequencies (even within the same band). m) Solid state rigs generally don't require any transmitter tuning adjustments. Just set the desired frequency, and transmit. 3. MORSE LESSON 8: .,? 4. Receiver specifications When you want to know how good a receiver is, you look at the "three S's": sensitivity, selectivity, and stability. a) SENSITIVITY is the receiver's ability to pick up weak signals. Usually this is limited by noise generated within the receiver. A receiver with more internal noise will be less sensitive. Sensitivity is measured as the number of microvolts of signal to produce a given signal-to-noise ratio. b) SELECTIVITY is the ability to separate signals close in frequency. This is determined by the "bandwidth," or how narrow a slice of frequencies the receiver is actually hearing. Bandwidth is measured in kHz. A narrow bandwidth is more selective, but the bandwidth has to be wide enough for the radio signal. SSB requires about 3 KHz. c) STABILITY is how well the receiver stays tuned to a certain frequency. Most receivers will slowly "drift" to a different frequency. Good ones drift only a few hundred Hertz per hour. d) PRACTICE QUESTIONS: 2-219, 2-221, 2-223, 2-225. 5. SSB Receiver [14] Almost all modern receivers are of the "superheterodyne" or "superhet" type. These all work by converting the radio frequency signal to an INTERMEDIATE FREQUENCY, or "IF". Most of the amplification and filtering takes place at the intermediate frequency. Here's how it works: a) The first stage is the ANTENNA. On the exam, this is considered part of the receiver. So remember that receivers always begin with the antenna. There may be a tuned circuit here (the "preselector"). b) Next is the RF AMPLIFIER. This increases the sensitivity of the receiver, and allows it to hear very weak signals. Note that the output of this stage is at the same frequency as the input (the RF frequency). c) The MIXER converts the radio frequency signal to the intermediate frequency. Recall that this is done by "mixing" two frequencies to get their sum and difference. So, the input of this stage is at the tunable R.F., and the output is at the fixed I.F. d) To make a fixed IF from the variable RF, we must add or subtract another variable frequency. This frequency is produced by the HIGH FREQUENCY OSCILLATOR, also called the "local oscillator." Since this oscillator determines which frequency will be converted to the IF, this is the tuning control. This also determines the STABILITY of the receiver. e) There are several mixer problems on the exam. 1) e.g. 2-240. IF is 9 MHz, receive signal is 13 MHz, what HFO? (Note that there are TWO possible answers, 4 & 22.) 2) e.g. 2-244. IF is 9 MHz, oscillator is 16 MHz, what RF? (Again, two possible answers: 7 & 25 MHz.) 3) TWO different radio frequencies will be converted to the same IF. One is the frequency you want, the other is the "image" frequency. "Image rejection" is how well the radio blocks this second frequency. f) After the mixer, the IF FILTER allows only signals at the intermediate frequency to pass. This determines the SELECTIVITY of the receiver. g) The IF AMPLIFIER amplifies the signal some more. Most of the amplification occurs here, since it's easy to make a good amplifier for a single frequency. Note: on some exam questions, the filter is considered part of the IF amplifier. h) SSB signals are converted back to audio by a PRODUCT DETECTOR. This must replace the carrier frequency that was suppressed in the transmitter, and demodulate the signal. i) The carrier frequency is supplied by the BEAT FREQUENCY OSCILLATOR. Thanks to the mixer, we only have to provide one frequency here: the Intermediate Frequency. For example, using a 9 MHz IF, the product detector will combine a 9 MHz SSB signal with a 9 MHz oscillator to produce audio. j) As a bonus, the B.F.O. will "beat" with a CW signal, in the product detector, producing an audio tone. So this same receiver works for SSB and CW. k) The audio signal is not strong enough to drive a loudspeaker or headphones, so an AUDIO (AF) AMPLIFIER makes it stronger. There may be a transformer to match the impedance of the amplifier to the loudspeaker. l) Finally is the LOUDSPEAKER or HEADPHONES. This is always the last block on a receiver diagram. m) PRACTICE QUESTIONS: 2-243, 2-245, 2-232, 2-152. Be sure to learn the block diagram well. 6. FM Receiver [14] The first six stages of an FM receiver are IDENTICAL. The only difference is in how the IF signal is converted to audio. a) The LIMITER gets rid of any amplitude variations in the signal. This is needed by the discriminator. b) The FREQUENCY DISCRIMINATOR converts frequency modulation to an audio signal. c) The AUDIO AMPLIFIER and SPEAKER/HEADPHONES are the same. So, only two stages are different. This should make it easier to memorize the receiver block diagrams. d) PRACTICE QUESTIONS: 2-236, 2-239, 2-159, 2-162. 7. BREAK 8. Receiver refinements Before we leave receivers, there are two improvements to the superheterodyne receiver that may appear on the exam. a) AUTOMATIC GAIN CONTROL (AGC) keeps strong signals from blasting your ears. Remember that a local station's radio signal may be a million times stronger than a distant one! When a strong signal is received, an AGC signal is fed back to the RF and IF amplifiers, forcing them to reduce their gain. b) DOUBLE CONVERSION solves the problem of image rejection. Remember that the mixer will accept TWO frequencies to produce the IF. Double conversion uses TWO intermediate frequencies, one after the other. This means two mixers, two local oscillators, and two IF amplifiers. The first frequency is chosen for the best image rejection. The second frequency is chosen for best selectivity. c) PRACTICE QUESTIONS: 2-247, 2-238, 2-246. 9. REGS: Equivalent Licenses [RIC-25 p.4-5,7-8] Several different licences allow the use of the amateur bands. These are listed on the RIC-25 handout, and yes, there may be an exam question about this. (READ THE LIST) 10. Repeaters a) REPEATERS let you cover a wide range on VHF. They do this by rebroadcasting your signal from a powerful transmitter, and also receiving and retransmitting the signal of the other station. They "relay" your signal. b) Here's the catch: repeaters can't retransmit on the SAME frequency that you're sending on. So it retransmits on a slightly different frequency. The difference in the two frequencies is the OFFSET. c) On 2 metres, the offset is normally 600 kHz, higher or lower. d) So, everyone using the repeater transmits on frequency A. Everyone listens on frequency B. The repeater relays signals from frequency A to frequency B. e) e.g. when you use the Owen Sound repeater, you should send on 146.340 MHz, and listen on 146.940 MHz. f) When you give out a repeater frequency, or see a listing in a repeater guide, you will give out the LISTEN frequency, and whether the sending-frequency offset is positive (600 kHz higher) or negative (600 kHz lower). g) e.g., for Owen Sound you would say "146.940 minus". This says to listen on 146.940 MHz, and to send on a frequency 600 kHz lower than this. (146.340 MHz.) h) PRACTICE QUESTION: 3-118. 11. MORSE REVIEW 8: .,? I. WEEK 5 - MORNING - Review 1. Final review 2. MORSE REVIEW 3. Exam advice a) usually your first impulse is right b) if you can't work the math backwards, try all the answers c) if you don't know, guess: no penalty for wrong answers J. WEEK 5 - AFTERNOON - Exams EXAMINER: Nick VE3MWU PROCTOR: Brad VE3RHJ 1. Code receiving exam (all students) 2. Written exam 1st shift (2 hours maximum) 3. Written exam 2nd shift (as 1st shift is finished) 4. Code sending exams (as written exams are finished) K. INDIVIDUAL ASSISTANCE Rather than cover this during the class presentation, answer these questions on an individual (one on one) basis, during breaks, lunchtime, etc. 1. *Buying ham equipment new a) dealers b) typical prices 2. *Buying ham equipment used a) local hams b) swapmeets c) swap nets d) packet listings e) reference information f) checking out the rig g) typical prices 3. *Sources for more information a) Georgian Bay ARC $35 to join for 1 year ($30 renewal) monthly meetings monthly newsletter weekly nets (2m, 80m) special events (e.g. Field Day) Owen Sound repeater VE3OSR BITNET Packet BBS VE3IJD people you can ask for help! b) Radio Amateurs of Canada $ per year our national amateur radio organization monthly The Canadian Amateur QSL Bureau Internet site www.rac.ca