\(10.5\) volts is the minimum allowable discharge voltage for a standard 12 volt lead acid battery to retain maximum cell life.

Discharging below this level can cause changes in the chemical nature of the cell which are irreversible, which can damage or destroy the cell.

For more info see Wikipedia: Lead-acid battery

Last edited by kd7bbc. Register to edit

Tags: arrl chapter 4 arrl module 15

High discharge current is an advantage of the low internal resistance of nickel-cadmium (NiCd) batteries. This makes them great to use in portable electronic devices and tools which require high current flow.

For more info see Wikipedia: Nickle-cadmium (NiCd) batteries

High Discharge Rate Lithium Polymer Battery 5C

Last edited by jeff00seattle. Register to edit

Tags: arrl chapter 4 arrl module 15

\(0.3\) Volts is the approximate junction threshold voltage of a germanium diode.

This threshold is the voltage over which the diode can conduct significant current. Different materials have different junction threshold voltages, so the value for each diode is determined by the properties of the material(s) used in its construction.

For example, a diode made of silicon has a junction threshold voltage of about \(0.7\) Volts.

Silly Hint:

G for Germanium is about \(\frac{3}{10}\) (\(0.3\) V) of the way through the alphabet while S for Silicon is about \(\frac{7}{10}\) (\(0.7\) V) of the way through the alphabet.

Silly Hint: the 3rd Reich started in Germany

For more info see Wikipedia: Diode

Last edited by kegarot128. Register to edit

Tags: arrl chapter 4 arrl module 14

(D). Carbon-zinc primary cell batteries should NEVER be recharged. The chemical reaction which generates current in these batteries is not reversible. Attempting to recharge the battery can cause acid and heat to be released, burning and corroding whatever it comes into contact with. DO NOT RECHARGE.

For more info see Wikipedia: Carbon-zinc batteries

Silly Hint: Think "Z" in Zinc is at the END of the alphabet. A discharged Carbon-Zinc battery has reached the END of its useful life. Or, remember that Carbon-Zinc batteries are alkaline batteries, which you throw away or recycle when they go dead.

Last edited by kc7ywx. Register to edit

Tags: arrl chapter 4 arrl module 15

The approximate junction threshold voltage of a conventional silicon diode is \(0.7\) volts.

This threshold voltage is the voltage where the diode can start to conduct the greater part of the current. The material a diode is made from is a significant factor in what the threshold voltage will be. For example, the germanium diode has a junction threshold of about \(0.3\) volts.

Silly Hint:

S for Silicon, S for Seven. Also, the letter S is about \(\frac{7}{10}\) (0.7 volts) of the way through the alphabet. (As opposed to Germanium where G is about .3 the through)

Silicon has (7) letters***

For more info see Wikipedia: Diode

Last edited by thatshortgymchick772. Register to edit

Tags: arrl chapter 4 arrl module 14

(A). The Schottky diode has a lower capacitance in an RF switching circuit as compared to a standard silicon diode. This diode has a low threshold voltage and very fast switching action which makes it a good choice for using in various switching circuits.

For more info see Wikipedia: Schottky diode

Last edited by ssussex. Register to edit

Tags: arrl chapter 4 arrl module 14

The stable operation points for a bipolar transistor used as a switch in a logic circuit are its saturation and cut-off regions. The saturation region acts as a good "full on" switch position, whereas the cut-off region acts as a good "full off" switch position.

For more info see wikipedia: Bipolar junction transistor

HINT: Famous Painter Van Gogh was BIPOLAR. He used SATURATED colors and he CUT OFF his ear.

Last edited by missourib. Register to edit

Tags: arrl chapter 4 arrl module 14

The cases of some large power transistors must be insulated from ground to avoid shorting the collector or drain voltage to ground. The case of the transistor may be connected to the collector to keep the transistor from overheating, but having a connection to ground, may cause the collector and transistor to drain or short out.

For more info see Wikipedia: Transistor

Last edited by danielbaileypdx. Register to edit

Tags: arrl chapter 4 arrl module 14

A MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is constructed so that the gate is separated from the channel with a thin insulating layer.

Why? Because the electromagnetic "field" in the name needs a dead end at the gate. The field is created when positive or negative charges accumulate on the gate electrode. The field pushes or pulls the electrons and holes within the nearby N-type and P-type materials, which opens or shuts the channel between gate and source as desired for the circuit under construction.

The pile-up of charges only works because there is nowhere for them to go (open circuit). The gate must be insulated from the rest of the transistor. If there was a short circuit, the charges would follow the path of least resistance, no charges would build up, and the "field effect" wouldn't work correctly.

For more info see Wikipedia: MOSFET

Silly hints:

• The correct answer has the key word "Channel."
• This is kind of a "gotcha" question, so you can think "GATe"+"CHAnnel" for "GAT-CHA."

Last edited by nicenjehr. Register to edit

Tags: arrl chapter 4 arrl module 14

The control grid is the element of a triode vacuum tube used to regulate the flow of electrons between cathode and plate.

For more info see Wikipedia: Control grid

Hint: to “regulate” is to “Control” or remember that a triode tube has a control grid.

Last edited by edponce@yahoo.com. Register to edit

Tags: arrl chapter 4 arrl module 14

(B). A Field Effect Transistor is the device listed which is most like a vacuum tube in its general operating characteristics. It acts like the control grid in a vacuum tube system to control the flow of electrons between the drain and the source, just like the plate and cathode of the tube system.

For more info see Wikipedia: Field-Effect Transistor (FET)

Last edited by heroiclemon. Register to edit

Tags: arrl chapter 4 arrl module 14

The screen grid insulates/isolates the control grid from the plate which helps counteract the Miller effect by reducing the grid-to-plate capacitance.

Hint: SCREEN it to reduce it.

For more info see Wikipedia: Vacuum tube

Last edited by nrunner. Register to edit

Tags: arrl chapter 4 arrl module 14

All of these choices are correct

Consider a common type of polarized capacitor: an electrolytic capacitor. Electrolytic capacitors must be connected in the way specified, since the dielectric, usually a thin film of metal oxide, rapidly breaks down when current in the wrong direction is applied.

When the dielectric breaks down, the two "plates" of the capacitor can short out, generating a large amount of current to go through the capacitor and causing massive heating. These rapid and violent changes can result in a venting of hot liquid, or sometimes in dangerous explosions.

Last edited by kd7bbc. Register to edit

Tags: arrl chapter 4 arrl module 12

Ceramic capacitors have the advantage over other types of capacitors in they provide good function at comparatively low cost.

Silly hint: Ceramic Capacitors are Cheap

For more info see: ceramic capacitors

Last edited by kd7bbc. Register to edit

Tags: arrl chapter 4 arrl module 12

An advantage of electrolytic capacitors is that they have high capacitance for given volume.

These capacitors are often used in power supplies for AC voltage filtering.

They are polarized and must be placed in the circuit in the proper orientation, as reverse-voltages can cause catastrophic (explosive) failure. Bad electrolytic caps can swell and leak the electrolyte out the vent grooves notched in the top, appearing as a crusty substance. Also the electrolytic capacitors may have large variations in capacitance due to their method of manufacture.

For more info see: Electrolytic capacitors

Last edited by kd7bbc. Register to edit

Tags: arrl chapter 4 arrl module 12

(C). The resistance of a resistor will change depending on the resistor's temperature coefficient. Most resistors will increase in resistance with increases in temperature, in other words they have a positive correlation or positive coefficient between resistance and temperature.

For more info see Wikipedia: Resistors

Last edited by N8GCU. Register to edit

Tags: arrl chapter 4 arrl module 12

One reason not to use wire-wound resistors in an RF circuit is that the resistor's inductance could make the circuit performance unpredictable.

The construction of a wire wound resistor is VERY similar to that of an inductor. So in situations where extra inductance may be an issue (such as RF circuits), they are not a good component choice.

Silly Hint: Something that is Unpredictable is usually something you do NOT choose.

For more info see Wikipedia: Wire-wound resistors

Last edited by kf0gtr. Register to edit

Tags: arrl chapter 4 arrl module 12

This question could be asking about a couple of things:

(1) What advantage does a toroid core provide as opposed to a straight core?

(2) What advantage does a ferrite core provide as opposed to a powdered iron core?

Based on the correct answer, it seems like it's only asking about toroid versus straight.

Toroids have become popular because the amount of magnetic flux that leaks outside of the core itself is low, which makes it more efficient and it radiates less electromagnetic interference.

Additionally, toroid cores are a closed loop. In a straight core the magnetic field has to go pretty far from one end to enter at the other. This means that the toroid will typically produce a larger inductance.

Finally, by varying the size and thickness and characteristics of the ferrite itself, you can optimize a ferrite toroid for different frequencies.

Silly Hint: the TOROIDAL inductor gives you the TOTAL package.

For more info see Wikipedia: Toroidal inductor

Last edited by glitteribbon. Register to edit

Tags: arrl chapter 4 arrl module 12

(C). The winding axes or coils of solenoid inductors should be placed at right angles to minimize their mutual inductance. Because each solenoid has an associated magnetic field, it is important to use this arrangement to avoid these fields interacting with each other.

For more info see Wikipedia: Solenoid

Last edited by ssussex. Register to edit

Tags: arrl chapter 4 arrl module 12