General Exam-Circuit Components

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rledwith
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General Exam-Circuit Components
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2013-07-15 18:00:34
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Amateur Radio General Exam - G6 Question Set - Circuit Components
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  1. G6A01 Which of the following is an important characteristic for capacitors used to filter the DC output of a switching power supply?
    A. Low equivalent series resistance
    B. High equivalent series resistance
    C. Low Temperature coefficient
    D. High Temperature coefficient
    • (A)
    • It is important to use filter capacitors that have a low equivalent series resistance (ESR) rating for the output filter of a switching power supply. Low ESR means that currents flowing into and out of the capacitor as it smoothes the output voltage will not cause ripple (voltage variations) and losses that heat the capacitor.
  2. G6A02 Which of the following types of capacitors are often used in power supply circuits to filter the rectified AC?
    A. Disc ceramic
    B. Vacuum variable
    C. Mica
    D. Electrolytic
    • (D)
    • Because electrolytic capacitors can be made with the required high capacitance value in a small package, they are often used in power supply circuits to filter the rectified ac voltage.
  3. G6A03 Which of the following is an advantage of ceramic capacitors as compared to other types of capacitors?
    A. Tight tolerance
    B. High stability
    C. High capacitance for given volume
    D. Comparatively low cost
    • (D)
    • The primary advantage of ceramic capacitors is that they offer good performance at low cost. Ceramic capacitors are usually used as bypass capacitors that filter out high-frequency ac voltages from dc and low-frequency signal connections.
  4. G6A04 Which of the following is an advantage of an electrolytic capacitor?
    A. Tight tolerance
    B. Non-polarized
    C. High capacitance for given volume
    D. Inexpensive RF capacitor
    • (C)
    • Electrolytic capacitors are designed to provide large values of capacitance for energy storage and ac voltage filtering. Their construction, shown in the illustration, provides relatively high capacitance in a small volume. The tradeoff is that dc voltage applied to them must always be of the same polarity and the manufacturing technique leads to rather wide variations in capacitance.
  5. G6A05 Which of the following is one effect of lead inductance in a capacitor used at VHF and above?
    A. Effective capacitance may be reduced
    B. Voltage rating may be reduced
    C. ESR may be reduced
    D. The polarity of the capacitor might become reversed
    • (A)
    • Lead inductance creates a small inductance in series with the capacitor. At low frequencies, lead inductance can be ignored but at VHF and higher frequencies, the inductive reactance begins to cancel the capacitor’s own reactance, reducing the effective capacitance dramatically! Capacitors to be used at these high frequencies must have very short leads.
  6. G6A06 What will happen to the resistance if the temperature of a resistor is increased?
    A. It will change depending on the resistor’s reactance coefficient
    B. It will stay the same
    C. It will change depending on the resistor's temperature coefficient
    D. It will become time dependent
    • (C)
    • The resistance of almost any substance changes when heated. The amount of change in a resistor’s value depends on its temperature coefficient. Most resistors have a positive temperature coefficient, meaning that resistance increases with temperature.
  7. G6A07 Which of the following is a reason not to use wire-wound resistors in an RF circuit?
    A. The resistor's tolerance value would not be adequate for such a circuit
    B. The resistor's inductance could make circuit performance unpredictable
    C. The resistor could overheat
    D. The resistor's internal capacitance would detune the circuit
    • (B)
    • Wire-wound resistors are made exactly as their name implies. A length of “resistance wire” — usually Nichrome — is wound around a ceramic form. The wire has some specific resistance per length of wire, so the length of wire is chosen to give the desired resistance. Because a long length of wire is difficult to accommodate in an electronics circuit, the wire is wound on the form to reduce the overall length of the resistor. The resistor is then coated with a ceramic or other insulating material to protect the wire. If this construction method sounds like an inductor to you, you are absolutely correct! It is not a good idea to use wire-wound resistors in any RF circuits or anywhere you don’t want some extra amount of inductance to be included in the circuit. The extra inductance will detune any resonant circuit of which it is part or add unwanted inductive reactance to signal paths.
  8. G6A08 Which of the following describes a thermistor?
    A. A resistor that is resistant to changes in value with temperature variations
    B. A device having a specific change in resistance with temperature variations
    C. A special type of transistor for use at very cold temperatures
    D. A capacitor that changes value with temperature
    • (B)
    • All resistors change value to some degree with temperature. A thermistor is a special type of resistor whose change in value with temperature is precisely controlled so that it can be used as a temperature sensor.
  9. G6A09 What is an advantage of using a ferrite core toroidal inductor?
    A. Large values of inductance may be obtained
    B. The magnetic properties of the core may be optimized for a specific range of frequencies
    C. Most of the magnetic field is contained in the core
    D. All of these choices are correct
    • (D)
    • Because a toroid core offers a continuous, circular path for magnetic flux, nearly all of a toroidal inductor’s magnetic field in contained inside the core. This gives a toroidal inductor a self-shielding property that makes them ideal for use in RF circuits, where you do not want interaction between nearby inductors. Ferrite is a ceramic containing iron compounds. Ferrite and powdered-iron toroid cores both have high permeabilities (the ability to store magnetic energy) make it possible to obtain large values of inductance in a relatively small package, as compared to the number of turns that would be required with an air-core inductor. Toroid cores are made in different mixes” for use over various frequency ranges. An inductor’s core is said to be saturated when the current through the inductor creates a stronger magnetic field than can be stored in the core. For most inductor applications, you don ot want to saturate the core material. For some switched-mode power supply designs, however, the transformer is designed so the core saturates and creates an output pulse where the input voltage goes above a certain level. This type of design uses toroidal inductors with ferrite cores. All of the answer choices are true statements. So answer D is correct.
  10. G6A10 How should the winding axes of solenoid inductors be placed to minimize their mutual inductance?
    A. In line
    B. Parallel to each other
    C. At right angles
    D. Interleaved
    • (C)
    • An inductor that is formed by winding a coil of wire on a straight coil form of either air or a magnetic material is called a solenoid inductor. The magnetic field associated with a solenoid core extends through the center of the core and then around the outside of the coil. To minimize any interaction between the magnetic fields around solenoid inductors in a circuit, the coils should be placed so that the axes along which the wire is wound are at right angles to each other. (To ensure minimum interaction between solenoid coils you might also have to place each inductor inside its own shielded enclosure.)
  11. G6A11 Why would it be important to minimize the mutual inductance between two inductors?
    A. To increase the energy transfer between circuits
    B. To reduce unwanted coupling between circuits
    C. To reduce conducted emissions
    D. To increase the self-resonant frequency of the inductors
    • (B)
    • It is important to minimize unwanted mutual inductance between two inductors to prevent coupling – transferring energy – between different circuit stages.
  12. G6A12 What is a common name for an inductor used to help smooth the DC output from the rectifier in a conventional power supply?
    A. Back EMF choke
    B. Repulsion coil
    C. Charging inductor
    D. Filter choke
    • (D)
    • A filter choke is an inductor that is connected in series with the output of a power supply. It works with the filter capacitor to smooth the rectified ac from the rectifier into dc. The inductor is called a choke because it “chokes off” the variations in voltage at its input.
  13. G6A13 What is an effect of inter-turn capacitance in an inductor?
    A. The magnetic field may become inverted
    B. The inductor may become self resonant at some frequencies
    C. The permeability will increase
    D. The voltage rating may be exceeded
    • (B)
    • Inter-turn capacitance is created by adjacent turns of wire separated by air or their insulation. Even though the turns of wire are connected, the small separation between the wire surfaces creates a small capacitance. In a coil of many turns, the inter-turn capacitance can become significant. At high frequencies, the combination of the coil’s inductance and the inter-turn capacitance can become a series- or parallel-resonant circuit!
  14. G6B01 What is the peak-inverse-voltage rating of a rectifier?
    A. The maximum voltage the rectifier will handle in the conducting direction
    B. 1.4 times the AC frequency
    C. The maximum voltage the rectifier will handle in the non-conducting direction
    D. 2.8 times the AC frequency
    • (C)
    • Power-supply rectifier diodes are made from semiconductor material. Diodes allow current to flow only in one direction. If the voltage is high enough, however, current can be forced to flow in the opposite direction, often destroying the diode. The peak inverse voltage rating (PIV) of a rectifier diode is the maximum reverse voltage that should ever be applied to the diode--it is guaranteed to withstand that voltage.
  15. G6B02 What are two major ratings that must not be exceeded for silicon diode rectifiers?
    A. Peak inverse voltage; average forward current
    B. Average power; average voltage
    C. Capacitive reactance; avalanche voltage
    D. Peak load impedance; peak voltage
    • (A)
    • Peak inverse voltage and average forward current are two major ratings that must not be exceeded for silicon diode rectifiers. The peak inverse voltage rating (PIV) of a rectifier diode is the maximum reverse voltage that should ever be applied to the diode--it is guaranteed to withstand that voltage. The maximum average forward current is the other major rating that must not be exceeded. Forward current causes power to be dissipated in the diode due to the forward voltage drop (0.7 volts in silicon rectifiers). The amount of power is 0.7 V times the average forward current. Too much current overheats and destroys the diode.
  16. G6B03 What is the approximate junction threshold voltage of a germanium diode?
    A. 0.1 volt
    B. 0.3 volts
    C. 0.7 volts
    D. 1.0 volts
    • (B)
    • The junction threshold voltage is the voltage at which a diode begins to conduct significant current across its PN junction. The amount of voltage depends on the material from which the diode is constructed. The junction threshold voltage of silicon diodes is approximately 0.7 V and for germanium diodes approximately 0.3 V.
  17. G6B04 When two or more diodes are connected in parallel to increase current handling capacity, what is the purpose of the resistor connected in series with each diode?
    A. To ensure the thermal stability of the power supply
    B. To regulate the power supply output voltage
    C. To ensure that one diode doesn't carry most of the current
    D. To act as an inductor
    • (C)
    • Two or more diodes are sometimes connected in parallel to increase the current-handling ability of a circuit. There should always be a small resistor connected in series with each parallel diode. Without a resistor in series with each diode, one diode may conduct most of the current because of small variations in threshold voltage and that could destroy the diode by exceeding its average forward current rating. The resistor value should be chosen to provide a few tenths of a volt drop at the expected forward current.
  18. G6B05 What is the approximate junction threshold voltage of a conventional silicon diode?
    A. 0.1 volt
    B. 0.3 volts
    C. 0.7 volts
    D. 1.0 volts
    • (C)
    • The junction threshold voltage is the voltage at which a diode begins to conduct significant current across its PN junction. The amount of voltage depends on the material from which the diode is constructed. The junction threshold voltage of silicon diodes is approximately 0.7 V and for germanium diodes approximately 0.3 V.
  19. G6B06 Which of the following is an advantage of using a Schottky diode in an RF switching circuit as compared to a standard silicon diode?
    A. Lower capacitance
    B. Lower inductance
    C. Longer switching times
    D. Higher breakdown voltage
    • (A)
    • The construction of a Schottky diode results in much lower capacitance between the cathode and the anode. This makes the diode respond better to high-frequency signals in a switching power supply, digital logic, or an RF circuit.
  20. G6B07 What are the stable operating points for a bipolar transistor used as a switch in a logic circuit?
    A. Its saturation and cut-off regions
    B. Its active region (between the cut-off and saturation regions)
    C. Its peak and valley current points
    D. Its enhancement and deletion modes
    • (A)
    • When a bipolar transistor is used as a switch in a logic circuit it is important that the switch either be “all the way on” or “all the way off.” This is achieved by operating the transistor either in its saturation region to turn the switch on, or in its cut-off region to turn the switch off.
  21. G6B08 Why must the cases of some large power transistors be insulated from ground?
    A. To increase the beta of the transistor
    B. To improve the power dissipation capability
    C. To reduce stray capacitance
    D. To avoid shorting the collector or drain voltage to ground
    • (D)
    • On some power transistors the collector is connected to the case to improve the transfer of heat away from the semiconductor material. This helps keep the transistor from overheating when controlling high currents but requires that the case of the transistor (usually connected to the collector) be insulated from ground since most circuits do not ground the collector.
  22. G6B09 Which of the following describes the construction of a MOSFET?
    A. The gate is formed by a back-biased junction
    B. The gate is separated from the channel with a thin insulating layer
    C. The source is separated from the drain by a thin insulating layer
    D. The source is formed by depositing metal on silicon
    • (B)
    • A MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is similar to a JFET (Junction Field Effect Transistor), but instead of the gate electrode being in direct contact with the channel between drain and source, it is insulated by a thin insulating layer of oxide. The gate voltage still controls electron flow between the drain and source, but very little current flows in the gate circuit.
  23. G6B10 Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate?
    A. Control grid
    B. Heater
    C. Screen Grid
    D. Trigger electrode
    • (A)
    • The control grid is closest to the cathode, the element of the tube that generates the electrons. By varying the control grid voltage with respect to the cathode voltage, electron flow between cathode and plate can be controlled.
  24. G6B11 Which of the following solid state devices is most like a vacuum tube in its general operating characteristics?
    A. A bipolar transistor
    B. A Field Effect Transistor
    C. A tunnel diode
    D. A varistor
    • (B)
    • A Field-Effect Transistor (FET) acts very much like a vacuum tube with the gate electrode taking the role of the control grid, controlling electron flow between the drain and source that correspond to the plate and cathode, respectively.
  25. G6B12 What is the primary purpose of a screen grid in a vacuum tube?
    A. To reduce grid-to-plate capacitance
    B. To increase efficiency
    C. To increase the control grid resistance
    D. To decrease plate resistance
    • (A)
    • The screen grid is placed between the plate and control grid and kept at a constant voltage. This isolates the control grid from the plate and reduces the capacitance between them.
  26. G6B13 What is an advantage of the low internal resistance of nickel-cadmium batteries?
    A. Long life
    B. High discharge current
    C. High voltage

    D. Rapid recharge
    • (B)
    • Nickel-Cadmium (NiCd) batteries are constructed so that they can supply large quantities of current very quickly. This makes them useful in portable power tools and radio transceivers.
  27. G6B14 What is the minimum allowable discharge voltage for maximum life of a standard 12 volt lead acid battery?
    A. 6 volts
    B. 8.5 volts
    C. 10.5 volts
    D. 12 volts
    • (C)
    • Standard 12-volt lead-acid batteries are composed of six 2-volt cells connected in series. Each cell should not be discharged below 1.75 volts to avoid causing irreversible chemical changes that damage the cell. Thus, the minimum voltage for a standard 12-volt battery is 6 x 1.75 = 10.5 volts.
  28. G6B15 When is it acceptable to recharge a carbon-zinc primary cell?
    A. As long as the voltage has not been allowed to drop below 1.0 volt
    B. When the cell is kept warm during the recharging period
    C. When a constant current charger is used
    D. Never
    • (D)
    • Carbon-zinc batteries are not rechargeable because the chemical reaction that powers them cannot be reversed. Do not attempt to recharge them! If current is forced back through the cell, the resulting chemical reaction releases acid and heat that may breach the battery’s case, damaging whatever houses the battery.
  29. G6C01 Which of the following is an analog integrated circuit?
    A. NAND Gate
    B. Microprocessor
    C. Frequency Counter
    D. Linear voltage regulator
    • (D)
    • A linear voltage regulator is composed of a transistor, a voltage reference diode, and an amplifier that compares the circuit output voltage to the voltage reference. The regulator continuously varies the transistor current to keep the output voltage constant. Operation over a continuous range of voltages and currents is what analog integrated circuits do.
  30. G6C02 What is meant by the term MMIC?
    A. Multi Megabyte Integrated Circuit
    B. Monolithic Microwave Integrated Circuit
    C. Military-specification Manufactured Integrated Circuit
    D. Mode Modulated Integrated Circuit
    • (B)
    • An MMIC is a special type of analog IC containing circuits to perform RF operations such as amplification, modulation and demodulation, and mixing at HF through microwave frequencies. Some MMICs combine several functions, acting as an entire receiver front end, for example. The MMIC is what enables communications engineers to construct low-cost, hand-held mobile phones and GPS receivers, among other sophisticated examples of wireless technology.
  31. G6C03 Which of the following is an advantage of CMOS integrated circuits compared to TTL integrated circuits?
    A. Low power consumption
    B. High power handling capability
    C. Better suited for RF amplification
    D. Better suited for power supply regulation
    • (A)
    • Integrated circuits based on CMOS (Complementary Metal Oxide Semiconductor) technology consume very little current when operating, only drawing significant power when switching between ON and OFF states.
  32. G6C04 What is meant by the term ROM?
    A. Resistor Operated Memory
    B. Read Only Memory
    C. Random Operational Memory
    D. Resistant
    to Overload Memory
    • (B)
    • ROM, or read only memory, contains data or program instructions that do not need to be changed. ROM is used to prevent unauthorized changes.
  33. G6C05 What is meant when memory is characterized as “non-volatile”?
    A. It is resistant to radiation damage
    B. It is resistant to high temperatures
    C. The stored information is maintained even if power is removed
    D. The stored information cannot be changed once written
    • (C)
    • Non-volatile memory can retain stored data even if power is removed and restored. It never needs to have the data “refreshed.” Volatile memory loses the data if power is removed and often needs to have the data refreshed while in operation, such as for dynamic types of memory.
  34. G6C06 Which of the following describes an integrated circuit operational amplifier?
    A. Digital
    B. MMIC
    C. Programmable Logic
    D. Analog
    • (D)
    • An operational amplifier, or op amp, is an analog circuit, operating over a continuous range of voltage and current.
  35. G6C07 What is one disadvantage of an incandescent indicator compared to an LED?
    A. Low power consumption
    B. High speed
    C. Long life
    D. High power consumption
    • (D)
    • Incandescent indicators (lamps) are bright but they waste as heat most of the energy supplied to them. For the same amount of light output, LEDs are much more power-efficient than incandescents.
  36. G6C08 How is an LED biased when emitting light?
    A. Beyond cutoff
    B. At the Zener voltage
    C. Reverse Biased
    D. Forward Biased
    • (D)
    • An LED emits light when forward biased so that current flows through the PN-junction of the diode. Photons of light are given off when the electrons from the N-type material combine with the holes in the P-type material.
  37. G6C09 Which of the following is a characteristic of a liquid crystal display?
    A. It requires ambient or back lighting
    B. It offers a wide dynamic range
    C. It has a wide viewing angle
    D. All of these choices are correct
    • (A)
    • A liquid crystal display (LCD) works by blocking the transmission of light through an otherwise transparent layer of liquid crystals. Transparent electrodes are printed on the glass layers on either side of the liquid crystals to form the pattern of the digits, characters, and symbols. When voltage of the right polarity is applied between the electrodes, the liquid crystals twist into a pattern that blocks light. This is why an LCD requires ambient light to reflect off the back of the display or an active source of light behind the liquid crystals (back-lighting) in order to see the desired pattern.
  38. G6C10 What two devices in an Amateur Radio station might be connected using a USB interface?
    A. Computer and transceiver
    B. Microphone and transceiver
    C. Amplifier and antenna
    D. Power supply and amplifier
    • (A)
    • A USB (Universal Serial Bus) interface is a means of exchanging digital data in a serial stream (meaning one bit at a time). The computer and transceiver are the most likely to communicate over such an interface.
  39. G6C11 What is a microprocessor?
    A. A low power analog signal processor used as a microwave detector
    B. A computer on a single integrated circuit
    C. A microwave detector, amplifier, and local oscillator on a single integrated circuit
    D. A low voltage amplifier used in a microwave transmitter modulator stage
    • (B)
    • These miniature computers on a single IC consist of thousands of digital gates and logic elements that can retrieve program instructions (known as machine language) and execute them using digital data. Simple microprocessors may be little more than a set of registers that store and exchange data for the program instructions. Complex microprocessors may contain sub-processors that are dedicated to special functions, sophisticated communications interfaces, or include analog-digital converters to provide an all-in-one DSP platform.
  40. G6C12 Which of the following connectors would be a good choice for a serial data port?
    A. PL-259
    B. Type N
    C. Type SMA
    D. DE-9
    • (D)
    • RS-232 serial data interfaces are common in amateur equipment. The most common connector used for these interfaces is the 9-pin D-style DE-9, also called a DB-9. These connectors are usually found on personal computers as COM ports. RS-232 interfaces are being phased out in favor of USB and other interfaces that can transfer data at higher rates.
  41. G6C13 Which of these connector types is commonly used for RF service at frequencies up to 150 MHz?
    A. Octal
    B. RJ-11
    C. PL-259
    D. DB-25
    • (C)
    • The UHF connector family includes the PL-259 cable plug and SO-239 chassis-mounted socket. It is the most popular type of RF connector used on amateur equipment. UHF does not refer to a frequency range in this case.
  42. G6C14 Which of these connector types is commonly used for audio signals in Amateur Radio stations?
    A. PL-259
    B. BNC
    C. RCA Phono
    D. Type N
    • (C)
    • The RCA phono connector is the most common audio signal connector for consumer electronics and a great deal of amateur equipment. The connector’s name derives from its early use by the RCA Company for audio connectors and its subsequent popularity for the connection of phonographs to amplifiers and receivers.
  43. G6C15 What is the main reason to use keyed connectors instead of non-keyed types?
    A. Prevention of use by unauthorized persons
    B. Reduced chance of incorrect mating
    C. Higher current carrying capacity
    D. All of these choices are correct
    • (B)
    • A keyed connector has an asymmetrical body shape or arrangement of contacts. This prevents reversed or improper circuit connections that lead to improper operation or damage to the equipment. Do not force keyed connectors together if they are not oriented correctly.
  44. G6C16 Which of the following describes a type-N connector?
    A. A moisture-resistant RF connector useful to 10 GHz
    B. A small bayonet connector used for data circuits
    C. A threaded connector used for hydraulic systems
    D. An audio connector used in surround-sound installations
    (A)
  45. G6C17 What is the general description of a DIN type connector?
    A. A special connector for microwave interfacing
    B. A DC power connector rated for currents between 30 and 50 amperes
    C. A family of multiple circuit connectors suitable for audio and control signals
    D. A special watertight connector for use in marine applications
    • (C)
    • Multiple-pin DIN and Mini-DIN connectors are the standard for accessory connectors on amateur equipment. DIN stands for the Deutsches Institut für Normung, the German standards organization. DIN and Mini-DIN connectors are keyed and have up to 9 pins.
  46. G6C18 What is a type SMA connector?
    A. A large bayonet-type connector usable at power levels in excess of 1 KW
    B. A small threaded connector suitable for signals up to several GHz
    C. A connector designed for serial multiple access signals
    D. A type of push-on connector intended for high-voltage applications
    • (B)
    • SMA connectors are small threaded connectors designed for miniature coaxial cable and are rated for use up to 18 GHz. Handheld transceivers often use SMA connectors for attaching antennas.

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