Ch2 Fundaments Flashcards
amplitude
the strength of a radio wave; continuously varies
oscillating
the continual change of the signal’s amplitude; the signal goes up and down as it oscillates
cycle
as the signal oscillates, each complete up-and-down sequence forms a cycle
frequency (f)
the number of cycles per second; represented by the lower-case f
hertz (Hz)
unit of measurement for frequency
period (T)
the period of the cycle (represented by capital-T) is its duration
reciprocal of the period 1/T
frequency is the reciprocal of the period; f = 1/T
harmonic
a signal with a frequency that is some multiple (x2, x3, x4 and so on) of a fundamental frequency; 2f is second harmonic etc
phase
position within a cycle; phase is used to compare how sine wave signals are aligned in time
degrees
used to measure a phase; there are 360 degrees in a sine wave
out of phase
if two sine waves have a phase difference of 180 degrees, one wave is increasing, the other decreasing
in phase
waves that have no phase difference and are increasing/decreasing at the same time
audio frequency (AF signals)
signals below 20 kHz that humans can hear
radio frequency (RF signals)
signals above 20 kHz (everything above what humans can hear)
radio spectrum
the range of radio signal frequencies: 20 kHz - several hundred GHz
band
a specific range of frequencies in which signals are used for a common purpose or have similar characteristics
AM band
535 - 1700 kHz
FM band
88 - 108 MHz
amateur bands (ham bands)
VHF 30 - 300 MHz; UHF 300 MHz - 3 GHz; HF (Shortwave) 3 - 30 MHz
spectrum display
organizes signals according to their frequencies and signal strength
wavelength (λ)
the wavelength of a radio wave is the distance that it travels during one complete cycle; represented by the Greek letter lambda
speed of light (c)
all radio waves travel at the speed of light; represented by the lower-case c; the speed of light is constant at 300,000,000 or 3 x 10⁸ meters per second
wavelength/frequency relationship
λ = c / f Because the speed is constant, wavelength and frequency have an inverse relationship
amateur bands as wavelengths
Ex: “I’ll call you on 2 meters. Let’s try 146.52 MHz.” The frequency band is referred to as 2 meters because the radio waves are approximately that long.
wavelength of a 1 MHz radio wave
λ = c / f; λ = 300 Meters per second / 1 MHz
wavelength of a 1 MHz radio wave
λ = c / f; λ = 300 Meters per second / 1 MHz = 300 meters
convert from meters to feet
multiply the wavelength in meters by 3.28
convert from feet to meters
divide the wavelength in feet by 3.28
convert from meters to inches
multiply the wavelength in meters by 39.37
three basic elements of an amateur station
transmitter (XMTR), receiver (RCVR), and antenna
transceiver (XCVR)
AKA “rigs”; combines all three basic elements in one piece of equipment
feed line
AKA “transmission lines”; connects the antenna to the transmitter or receiver
transmit-receive (TR) switch
allows a transmitter and receiver to share a single antenna
repeater
located on high buildings or towers, a receiver and transmitter that will re-transmit the information from a received signal simultaneously on another frequency or channel; provide communications between low-power mobile and portable stations
duplex communication
the process repeaters use to re-transmit information simultaneously; instead of a transmit-receive switch, it uses a duplexer
