Basic Radio Theory Flashcards
Define: amplitude modulation.
A way of conveying information via amplitude variation.
Define: amplitude.
Variance from zero at some point on a radio wave.
Define: attenuation.
The weakening of radio waves due to absorption.
Define: carrier wave.
The waveform upon which modulation is overlaid.
Define: continuous power.
The average power consumed over time.
Define: critical angle.
The highest angle at which an emission returns to Earth.
Define: cycle.
One complete oscillation of a radio wave.
Define: dead space.
The gap between the last point where surface waves can be received and the first returning sky wave.
Define: diffraction.
A change in direction of waves as they pass through an opening or around a barrier in their path.
Define: Doppler effect.
The apparent change in frequency and wavelength of a wave caused by relative motion between the source of the wave and the observer.
Define: Doppler shift formula.
Doppler shift = Relative velocity / Transmitted wavelength
Define: ducting.
The forming of atmospheric layers which increase the range of space waves by causing them to follow the curvature of the Earth more.
Define: fading.
A type of signal interference (degradation) which occurs when there is no dead space between the transmitter and the receiver. In such instances the aerial receives sky waves and surface waves from the transmitter at the same time.
Define: frequency modulation.
A way of conveying information via frequency variation.
Define: frequency.
Cycles per period.
Define: hertz.
Measurement of frequency in cycles per second.
Define: minimum skip distance.
The distance between the transmitter and the first returning sky wave.
Define: modulation.
The process of embedding information onto waveforms.
Define: peak amplitude.
Maximum amplitude of a radio wave, either positive (above zero) or negative (below zero).
Define: peak-to-peak amplitude.
Positive and negative peak amplitudes of a radio wave added together.
Define: phase modulation
A way of conveying information via carrier wave phase reversal.
Define: phase shift.
The difference in phase angle between two waves.
Define: phase.
The position of a point on a wave (expressed in degrees).
Define: pulse modulation.
A way of conveying information via radio pulses.
Define: pulse power.
Power contained within a pulse.
Define: pulse train.
A series of pulses.
Define: pulse width.
Length of a pulse.
Define: reference phase.
The phase with its zero point on the positive gradient (at the origin).
Define: reflection.
A change in direction of waves when they bounce off a barrier.
Define: refraction.
A change in the direction of waves as they pass from one medium to another.
Define: suppressed carrier transmissions.
Signals transmitted without the carrier wave (less power used).
Define: the elements of an electromagnetic field?
An electric (E, parallel to the aerial) field and a magnetic (H, perpendicular to the aerial) field.
Define: unmodulated wave.
Continuous wave at a constant frequency.
Define: wavelength formula.
λ = c / f
Define: wavelength.
Distance a radio wave travels per cycle.
Describe the behaviour of:
(a) surface waves
(b) sky waves
(c) space waves
(a) they follow the curvature of the Earth
(b) they bounce back from the ionosphere
(c) they follow a straight line
How else is a pulse train called?
Pulse string.
How else is antenna called?
Aerial.
How else is dead space called?
Skip zone.
How else is peak-to-peak amplitude called?
Double amplitude.
How else is phase called?
Phase angle.
How else is pulse modulation called?
Keying.
How is pulse modulation achieved?
By rapidly switching the transmitter on and off.
List all the frequency bands.
VLF, LF, MF, HF, VHF, UHF, SHF, EHF.
List the ionospheric layers.
During day: D, E, F1, F2.
During night: E, F.
List the radio wave categories.
Surface waves, sky waves, space waves.
List the types of radio wave modulation.
Pulse, amplitude, frequency, and phase.
Regarding a receiving, vertically mounted, omnidirectional VHF antenna, state from which directions is the signal reception:
(a) the worst
(b) the best
(a) from directly above or below the antenna
(b) from directions perpendicular to the antenna
State how to convert from:
(a) kt to km/h
(b) km/h to m/h
(c) m/h to m/s
(a) multiply by 1.852
(b) multiply by 1,000
(c) divide by 3,600
State how to quickly (approximately) convert from:
(a) kt to km/h
(b) kt to m/s
(a) multiply by two and reduce the result by 10% of itself
(b) divide by two
State the frequency range and band of:
(a) AM signals
(b) FM signals
(a) 535 to 1700 kHz; MF
(b) 88 to 108 MHz; VHF
State the frequency range of:
(a) VLF
(b) LF
(c) MF
(d) HF
(e) VHF
(f) UHF
(g) SHF
(h) EHF
(a) 3 to 30 kHz
(b) 30 to 300 kHz
(c) 300 kHz to 3 MHz
(d) 3 MHz to 30 MHz
(e) 30 MHz to 300 MHz
(f) 300 MHz to 3 GHz
(g) 3 to 30 GHz
(h) 30 to 300 GHz
State the order of magnitude for the following prefixes:
(a) kilo
(b) mega
(c) giga
(a) 1,000
(b) 1,000,000
(c) 1,000,000,000
State the speed at which radio waves travel in:
(a) m/s
(b) km/s
(c) nm/s
(a) 300,000,000
(b) 300,000
(c) 162,000
State the standard notation and unit for:
(a) frequency
(b) speed of light
(c) wavelength
(a) f, Hz
(b) c, m/s
(c) λ, m
State the wavelength range of:
(a) VLF
(b) LF
(c) MF
(d) HF
(e) VHF
(f) UHF
(g) SHF
(h) EHF
(a) 100 to 10 km (myriametric)
(b) 10 to 1 km (kilometric)
(c) 1 km to 100 m (hectometric)
(d) 100 to 10 m (decametric)
(e) 10 to 1 m (metric)
(f) 1 m to 10 cm (decimetric)
(g) 10 to 1 cm (centimetric)
(h) 1 cm to 1 mm (millimetric)
State which frequency bands generally propagate as:
(a) surface and sky waves
(b) space waves
(a) VLF, LF, MF, HF
(b) VHF, UHF, SHF, EHF
What is the biggest advantage of slotted planar array antennae versus parabolic antennae?
Producing less side lobes, which is the primary source of energy loss.
What are the dimensions of an ideal half-wave dipole antenna?
The length of each pole should be a quarter of the signal wavelength.
The total length of poles should be half the signal wavelength.
What has the greatest effect on the ionosphere?
Solar activity.
What is the relationship between frequency and wavelength?
Wavelength is inversely proportional to frequency.
What is the shape of radio waves?
Sine curve.
What is the strength of the electromagnetic field proportional to?
The strength of the current.
What is the vertical extent of the ionosphere?
60 to 400 km.
When are waves said to be in anti-phase?
When the phase shift between them is 180°.
When are waves said to be in phase?
When the phase shift between them is 0°.
When is a phase said to be leading another phase?
When it is ahead of it.
Which type of current is used to create radio signals?
AC.
