G6 Circuit Components

C. 10.5 volts

A 12-volt lead-acid battery has six cells. The usual end-of-discharge limit is about 1.75 volts per cell (6 x 1.75 = 10.5 volts); discharging below that damages the plates and shortens battery life.

• A. 6 volts is only 1 volt per cell, a deep discharge that damages a lead-acid battery.
• B. 8.5 volts is about 1.4 volts per cell, well below the 10.5-volt limit, and shortens battery life.
• D. 12 volts is close to the battery's nominal voltage, and the battery still holds usable charge below it; the standard discharge limit is 10.5 volts.

B. High discharge current

A battery's internal resistance is in series with its output, so load current causes a voltage drop inside the battery. Low internal resistance keeps that drop small, so the battery can supply high current, such as a transmitter's peaks, without its voltage sagging much.

• A. Service life depends mainly on the chemistry, depth of discharge and charging practice, not on low internal resistance.
• C. A battery's voltage is set by its chemistry and number of cells, not by its internal resistance.
• D. Recharge speed depends mainly on the chemistry and the charger; the advantage of low internal resistance is on the discharge side.

B. 0.3 volts

A germanium junction diode begins to conduct significantly at a forward voltage of about 0.3 volts. That is lower than the roughly 0.7 volts a silicon junction diode needs.

• A. 0.1 volt is below the forward threshold of a germanium junction, about 0.3 volts.
• C. 0.7 volts is the approximate threshold of a silicon junction diode, not germanium.
• D. 1.0 volts is higher than the typical threshold of both germanium (about 0.3 V) and silicon (about 0.7 V) junctions.

C. High capacitance for a given volume

An electrolytic capacitor uses a very thin oxide layer as its dielectric, which gives a large capacitance in a small package. That makes it the usual choice for power supply filtering.

• A. Electrolytic capacitors have wide tolerances, commonly 20 percent or more, not tight ones.
• B. Electrolytic capacitors have relatively high leakage current compared with other types.
• D. Electrolytic capacitors have high internal inductance and resistance, which makes them poor at RF; ceramic types are used there.

C. 0.7 volts

A silicon junction diode begins to conduct significantly when forward biased by about 0.7 volts. Germanium diodes need only about 0.3 volts.

• A. 0.1 volt is far below the forward threshold of a silicon junction, about 0.7 volts.
• B. 0.3 volts is the approximate threshold of a germanium diode, not silicon.
• D. 1.0 volts is higher than the typical silicon junction threshold of about 0.7 volts.

B. The resistor’s inductance could make circuit performance unpredictable

A wire-wound resistor is made by winding resistance wire into a coil, which gives it inductance. At radio frequencies, that inductive reactance adds to the resistance and changes with frequency, so the circuit behaves unpredictably.

• A. Wire-wound resistors can be made to tight tolerances; tolerance is not the reason to avoid them at RF.
• C. Wire-wound resistors are often chosen because they handle power well; overheating is not the RF concern.
• D. The main unwanted property of a coiled wire is inductance, not capacitance; inductive reactance is what makes RF performance unpredictable.

A. Saturation and cutoff

A transistor switch is either fully off (cutoff, with no collector current) or fully on (saturation, with minimum voltage across it). Staying in these two states keeps the power dissipated in the transistor low.

• B. The active region between cutoff and saturation is where a transistor operates as a linear amplifier, not as a switch.
• C. Peak and valley current points describe the negative-resistance curve of devices such as tunnel diodes, not a bipolar transistor switch.
• D. Enhancement and depletion are modes of MOSFET operation, not operating points of a bipolar transistor.

D. Comparatively low cost

Low-voltage ceramic capacitors are simple to make and widely available, so they are comparatively inexpensive. They are common for bypassing and coupling, including at RF.

• A. Many common ceramic capacitors, especially high-capacitance types, have wide tolerances, so tight tolerance is not a general characteristic.
• B. General-purpose ceramic capacitors can change value noticeably with temperature and applied voltage, so high stability is not a general characteristic.
• C. High capacitance for a given volume is the characteristic associated with electrolytic capacitors.

B. The gate is separated from the channel by a thin insulating layer

MOSFET stands for metal-oxide-semiconductor field-effect transistor. Its gate is a conductor separated from the channel by a very thin insulating oxide layer, so the gate draws almost no current, and static discharge can puncture that layer.

• A. A gate formed by a reverse-biased (back-biased) junction describes a junction FET (JFET), not a MOSFET.
• C. The source and drain are connected by the channel; the insulating layer lies between the gate and the channel.
• D. The source is a doped region of the semiconductor; the metal in the name refers to the gate electrode above the oxide.

A. Control grid

The control grid sits between the cathode and the plate. A small voltage on it controls how many electrons reach the plate, which is how a tube amplifies.

• B. The suppressor grid, next to the plate in a pentode, returns secondary electrons knocked off the plate; it does not regulate the main electron flow.
• C. The screen grid reduces the capacitance between the control grid and the plate; it is not the element that regulates electron flow.
• D. A trigger electrode starts conduction in gas-filled devices such as flash tubes; it is not an element of an amplifying vacuum tube.

C. It becomes capacitive

Every inductor has some capacitance between its turns. At the self-resonant frequency, that capacitance resonates with the inductance; above it, the capacitance dominates and the component behaves like a capacitor.

• A. Reactance rises with frequency only below self-resonance; above it, the net reactance is capacitive and falls as frequency rises.
• B. Harmonics come from nonlinear devices; operating an inductor above self-resonance changes its reactance but does not generate harmonics.
• D. Operating above self-resonance changes how the inductor behaves in the circuit; it does not by itself cause the part to fail.

A. To reduce grid-to-plate capacitance

In a triode, capacitance between the control grid and the plate feeds output back to the input and can cause oscillation. A screen grid, placed between them and bypassed to ground for RF, shields the control grid from the plate and reduces that capacitance.

• B. Efficiency is set mainly by the amplifier's class and operating conditions; the screen grid's primary purpose is reducing grid-to-plate capacitance.
• C. The screen grid is a separate element; it does not change the resistance of the control grid.
• D. A screen grid raises plate resistance rather than decreasing it; its primary purpose is reducing grid-to-plate capacitance.

C. The composition, or “mix,” of materials used

Ferrite is a ceramic made from iron oxide combined with other metal oxides. The composition, or mix, sets the material's permeability and losses at different frequencies, which is why ferrite cores and beads are chosen by mix for a frequency range.

• A. Ferrites have low conductivity, which suits them to RF use, but the mix of materials is what sets their frequency behavior.
• B. Core thickness changes how much inductance a given number of turns produces, not how the material behaves across frequency.
• D. The ratio of outer to inner diameter affects inductance per turn, not the frequency range where the core material works well.

B. Monolithic Microwave Integrated Circuit

MMIC stands for Monolithic Microwave Integrated Circuit: a complete microwave circuit, such as a broadband amplifier, built on a single semiconductor chip. Amateurs often use MMICs as gain blocks at VHF, UHF and microwave frequencies.

• A. Multi-Mode Integrated Circuit is not the meaning; MMIC stands for Monolithic Microwave Integrated Circuit.
• C. Metal Monolayer Integrated Circuit is not the meaning; MMIC stands for Monolithic Microwave Integrated Circuit.
• D. Mode Modulated Integrated Circuit is not the meaning; MMIC stands for Monolithic Microwave Integrated Circuit.

A. Low power consumption

CMOS logic uses complementary pairs of transistors, so in either steady output state one transistor of each pair is off and almost no current flows. CMOS draws significant current mainly while switching, so it consumes much less power than TTL.

• B. CMOS logic ICs are low-power devices; high power handling is not an advantage of CMOS over TTL.
• C. CMOS and TTL are digital logic families; neither is designed for RF amplification.
• D. Power supply regulation is done by regulator circuits; it is not an advantage of either logic family.

C. 4 GHz

The BNC is a bayonet-locking 50-ohm connector that maintains low SWR up to about 4 GHz. It is common on test equipment and handheld radios.

• A. 50 MHz is far below the BNC's limit; it works well through VHF and UHF.
• B. 500 MHz is well within the BNC's range; its typical upper limit for low SWR is about 4 GHz.
• D. 40 GHz is well beyond a BNC connector's capability; that range requires precision microwave connectors.

D. All these choices are correct

A ferrite toroid has several advantages: the core's high permeability gives large inductance with few turns, the mix can be chosen for a frequency range, and the closed ring shape keeps most of the magnetic field inside the core, reducing coupling to nearby parts.

• A. Large inductance values are an advantage, because the core's permeability multiplies the inductance per turn, but this is only one of the listed advantages.
• B. Choosing the core material does optimize it for a frequency range, but this is only one of the listed advantages.
• C. The toroid's closed core does contain most of the magnetic field, but this is only one of the listed advantages.

D. Analog

An operational amplifier is a high-gain analog amplifier whose output varies continuously with its inputs. External feedback components set its gain and response for uses such as audio amplifiers and active filters.

• A. Digital ICs work with discrete high and low levels; an op-amp's output varies continuously.
• B. An MMIC is a microwave amplifier IC; an op-amp is a general-purpose analog amplifier used mostly at lower frequencies.
• C. Programmable logic devices are digital ICs configured to perform logic functions; an op-amp is an analog amplifier.

A. A moisture-resistant RF connector useful to 10 GHz

The type N is a threaded RF connector with a gasket that keeps out moisture and a constant-impedance design that performs well up to about 10 GHz. It is popular for outdoor, UHF and microwave feed line connections.

• B. A small bayonet connector used for data circuits describes a BNC-style connector; the type N is larger and threaded.
• C. Noise figure is a property of amplifiers and receivers, not connectors, and the type N is not limited to VHF.
• D. The type N is a different design from the PL-259 and does not mate with it; it is not a plated version of it.

D. Forward biased

An LED emits light when current flows through it in the forward direction: electrons and holes combine at the junction and release energy as light. It must be forward biased, usually with a series resistor to limit the current.

• A. The tunnel effect describes tunnel diodes, which have a negative-resistance region; LEDs do not operate there.
• B. The Zener voltage is a reverse breakdown point used by Zener diodes for voltage regulation, not for producing light.
• C. A reverse-biased LED blocks current and emits no light; too much reverse voltage can damage it.

A. By creating an impedance in the current’s path

Common-mode current flows on the outside of the coax shield, and a ferrite bead or core around the cable adds impedance to that path, reducing the current. The signal currents inside the coax produce equal and opposite fields that cancel, so the ferrite does not affect them.

• B. A ferrite does not convert current from one mode to another; it impedes the common-mode current and leaves the signal inside the coax alone.
• C. A ferrite is a passive core and does not generate a canceling current; it reduces the current by adding impedance to its path.
• D. Ferrites do not expel magnetic fields; their high permeability concentrates magnetic flux in the core, which is how they create impedance.

B. A small threaded connector suitable for signals up to several GHz

SMA (SubMiniature version A) is a small threaded RF connector that performs well up to several GHz. It is common on handheld radios, software-defined radio receivers and microwave equipment.

• A. SMA is a connector type, not an adaptor between types S and M; the name stands for SubMiniature version A.
• C. SMA does not refer to serial multiple access; it is an RF connector named SubMiniature version A.
• D. SMA connectors are threaded rather than push-on, and they are small RF connectors not intended for high voltage.

C. RCA Phono

RCA phono connectors are simple and inexpensive, so transceivers often use them for low-frequency and DC connections such as audio, keying, ALC and amplifier control lines. RF antenna connections use connectors such as the PL-259, BNC and type N.

• A. The PL-259 is an RF connector used mainly on antenna feed lines at HF and VHF.
• B. The BNC is a bayonet RF connector used for antennas and test equipment.
• D. The type N is an RF connector for UHF and microwave feed lines.