1. Components and Logic on The HamStudy Amateur Extra Class HamBook (2024 - 2028)

1.1 Diodes and Junctions

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Section 1.1: Diodes and Junctions #

You probably know the diode best as a one-way valve for current, the part that lets a power supply’s rectifier turn AC into DC. An LED is a diode too; it gives off light while it conducts.

That sells the diode short. With the right design, a diode can hold a voltage steady, pull the audio out of a radio signal, tune a receiver, or steer a signal from one path to another. To get those jobs out of it, you need a look inside, starting with the two kinds of material a diode is made from.

1.2 Transistors

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Section 1.2: Transistors #

Every transistor makes a demand on the stage that drives it. A bipolar junction transistor (BJT) asks for current: a small base current controls a larger current between collector and emitter. A field-effect transistor (FET) asks for voltage: the gate voltage controls current through a channel between source and drain. Both use the same doped semiconductor as a diode, so much of their behavior follows from the previous section.

1.3 Light and Electricity

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Section 1.3: Light and Electricity #

The solar panel charging a battery at Field Day turns sunlight into electricity, the reverse of what an LED does. Both depend on the band gap described earlier in this chapter. In an LED, electrons give up energy as light when they fall across the gap; a solar cell runs that process the other way. Light can carry information as well as power, so a circuit can also use it to measure brightness, pass a command across an insulating gap, or follow a turning knob.

1.4 Magnetic Components

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Section 1.4: Magnetic Components #

An inductor stores energy in the magnetic field around its coil. Wind the same wire on a ferrite ring instead of leaving it in air, and the inductance can rise many times over. That is why so many coils in radio equipment have cores. The core’s material and shape decide how much it helps, and they bring trade-offs of their own.

Material and Shape #

A core raises inductance by supporting a stronger magnetic field than air does. Magnetic flux is the field passing through an area, such as a core’s cross section. The winding’s current sets up a magnetizing field. Permeability describes how readily a material supports magnetic flux for a given magnetizing field. Don’t confuse permeability with permittivity, which describes a capacitor’s insulation.

1.5 Chips at Radio Frequencies

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Section 1.5: Chips at Radio Frequencies #

The stray inductance and capacitance that troubled the HF amplifier in the previous section can also interfere with signals we want. At UHF and microwave frequencies, a few millimeters of lead between a transistor or chip and its circuit, less than the width of a fingernail, can be enough to hold it back. A useful amplifier needs both a fast enough device and a package that lets it work.

1.6 Logic Gates and Levels

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Section 1.6: Logic Gates and Levels #

An amplifier should key up only when the radio asks and its protection circuit sees no fault. An AND gate enforces that rule: it gives a 1 only when both of its inputs are 1. A cooling fan may need a different rule: run when either a switch or a temperature sensor requests it. Which gate you choose depends on how those conditions should combine.

1.7 Timing and Digital Control

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Section 1.7: Timing and Digital Control #

The fan control in the previous section assumed tidy on/off requests. Real sensors are messier. A temperature sensor may produce a voltage that creeps upward with a little noise riding on it, and the controller must turn that into a steady decision.

From Level to Decision #

A comparator compares the sensor’s voltage with a reference voltage that sets the threshold. Its output goes high or low depending on which voltage is greater, giving the logic circuit an on/off state.