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March 16, 2019 - August 10, 2021
Speaking of contacts, any conversation between hams over the air is called a contact and starting a conversation is making contact. Attempting to make contact by transmitting your call sign is making a call or calling. If you’re making a “come in anybody” call to which any station can respond, that’s calling CQ. (“CQ” means “a general call.”)
The process of turning the transmitter’s output signal into radio waves that leave the antenna is called radiating or radiation.
T5B01 — How many milliamperes is 1.5 amperes? (1.5 A = 1,500 mA) T5B02 — What is another way to specify a radio signal frequency of 1,500,000 hertz? (1,500,000 Hz = 1,500 kHz = 1.5 MHz) T5B03 — How many volts are equal to one kilovolt? (1 kV = 1000 V) T5B04 — How many volts are equal to one microvolt? (1 μV = one one-millionth of a volt) T5B05 — Which of the following is equivalent to 500 milliwatts? (500 mW = 0.5 W) T5B06 — If an ammeter calibrated in amperes is used to measure a 3000-milliampere current, what reading would it show? (3,000 mA = 3 A) T5B07 — If a frequency display calibrated
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A specific range of frequencies in which signals are used for a common purpose or have similar characteristics is called a band.
The wavelength of a radio wave is the distance that it travels during one complete cycle. [T3B01] Wavelength is represented by the Greek letter lambda, λ.
All radio waves travel at the speed of light (represented by a lower-case c) in whatever medium they are traveling, such as air.
The speed of light in space and air is very close to 300 million meters per second (300,000,000 or 3 × 108 meters per second) [T3B11].
Because radio waves travel at a constant speed, one wavelength, λ = c / f. This means that as frequency increases, wavelengt...
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A radio wave can be referred to by wavelength or frequency because the wave is moving at a constant velocity — the speed of light. If you know the frequency of a radi...
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Because of this relationship, amateur bands are often referred to by wavelength.
The frequency band is referred to as “2 meters” because the radio waves are all approximately that long. The exact frequency then tells you precisely where to tune in the band.
To convert from meters to feet, multiply the wavelength in meters by 3.28. To get the wavelength in meters, divide feet by 3.28. To convert from meters to inches, multiply by 39.37. For example, the wavelength of an 80 meter signal in feet is: 80 meters × 3.28 feet per meter = 262.4 feet and the wavelength of a 70 cm signal in inches is: 0.7 meters × 39.37 inches per meter = 27.6 inches
Most amateur equipment combines the transmitter and receiver into a single piece of equipment called a transceiver (abbreviated XCVR).
Repeaters consist of a receiver and transmitter that re-transmit the information from a received signal simultaneously on another frequency or channel. [T1F09] This is called duplex communication.
Electric current (represented in equations by the symbol I or i) is the flow of electrons.
Voltage (represented in equations by the symbol E or e) is the electromotive force or electric potential that makes electrons move.
Voltage is measured with a voltmeter.
Current that flows in one direction all the time is direct current, abbreviated dc.
Current that regularly reverses direction is alternating current, abbreviated ac.
If two or more components such as light bulbs are connected in a circuit so that the same current must flow through all of them, that is a series circuit.
If two or more components are connected so that the same voltage is present across all of them, that is a parallel circuit.
At the junction of two components in a series circuit, as in Figure 3.3A, you can see that the current is unchanged — the same current flows in each component.
Ohm’s Law states that the current through a material is directly proportional to the voltage across it and inversely proportional to the material’s resistance. The higher the material’s resistance, the lower the current through it will be in response to a voltage across the material.
As an equation, Ohm’s Law is I = E / R. (You will also see this written as I =V / R with V representing voltage.)
I = E / R [T5D01] E = I × R [T5D02] R = E / I [T5D03]
T5D04 — What is the resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts? R = E / I = 90 V / 3 A = 30 Ω T5D05 — What is the resistance in a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes? R = E / I = 12 V / 1.5 A = 8 W T5D06 — What is the resistance of a circuit that draws 4 amperes from a 12-volt source? R = E / I = 12 V / 4 A = 3 W T5D07 — What is the current in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms? I = E / R = 120 V / 80 Ω = 1.5 A T5D08 — What is the current through
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Resistors have a certain value of resistance specified in ohms (Ω), kilohms (kΩ), or megohms (MΩ). The function of a resistor is to oppose the flow of electrical current in an ac or dc circuit, just as a valve in a water pipe restricts the flow through the pipe.
Capacitors store electrical energy in the electric field created by a voltage between two conducting surfaces or electrodes
separated by an insulator called a dielectric.
Storing energy this way is called capacitance, and it is meas...
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Inductors store energy in the magnetic field created by current flowing in a wire.
This is called inductance and it is measured in henrys (H).
Inductors are made from wire wound in a coil, sometimes around a core of magnetic material that concentrates the magnetic energy.
All three types of basic components are also available as adjustable or variable models. A variable resistor is also called a potentiometer (poh-ten-chee-AH-meh-tur) or pot because it is frequently used to adjust voltage or potential, such as for a volume control.
Transformers are made from two or more inductors that share their stored energy. This allows energy to be transferred from one inductor to another while changing the combination of voltage and current. For example, a transformer is used to transfer energy from household 120 V ac voltage to a lower voltage for other uses such as in electronic equipment.
The combination of resistance and reactance is called impedance, represented by the capital letter Z, and is also measured in ohms (Ω).
impedance is often used as a general term to mean the circuit’s opposition to ac current flow.
In a circuit with both capacitive and inductive reactance, at some frequency the two types of reactance will be equal and cancel each other out — a condition called resonance.
The frequency at which resonance occurs is the resonant frequency.
Circuits that contain both a capacitor and an inductor are called resonant circuits o...
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A tuned circuit acts as a filter, passing or rejecting signals at its resonant frequency.
A semiconductor that only allows current flow in one direction is called a diode.
A diode has two electrodes, an anode and a cathode.
As seen in Figure 3.11, on a diode the cathode is usually identified by a stripe marked on the component.
A special type of diode, the light-emitting diode or LED, gives off light when current flows through it.
Transistors are components made of N- and P-layer patterns, and can have three layers of semiconductor material.
With the appropriate external circuit and a source of power, transistors can amplify or switch voltages and currents.
