Physics & RF
B22 Modulation Techniques — Study Guide
This guide covers Modulation Techniques as part of Physics & RF. Start with the vocabulary, then try to answer each question before revealing the answer. Connect these facts to a real radio link or electrical circuit and practice the subject in the arcade when you are ready.
Acronyms first
| Term | Meaning |
|---|---|
| CW | Continuous Wave |
| AM | Amplitude Modulation |
| FM | Frequency Modulation |
| PM | Phase Modulation |
| SSB | Single Sideband |
| USB | Upper Sideband |
| LSB | Lower Sideband |
| PEP | Peak Envelope Power |
| ASK | Amplitude Shift Keying |
| FSK | Frequency Shift Keying |
| PSK | Phase Shift Keying |
Key facts
A carrier wave is…
a steady repeating sine wave from an oscillator, with no information by itself
What generates the carrier wave?
An oscillator
Modulation is…
varying a property (amplitude, frequency or phase) of a wave
An unmodulated carrier — constant amplitude and frequency, a pure tone — is a…
continuous wave (CW)
Which modulation varies the HEIGHT of the carrier while frequency stays constant?
AM
Which modulation varies the FREQUENCY while amplitude stays constant?
FM
Which modulation varies the instantaneous PHASE while amplitude and frequency stay constant?
PM
PM is a type of…
angle modulation
In AM, power is split between the carrier and…
an upper and lower sideband
Single sideband (SSB) transmits…
one sideband, with the carrier and other sideband suppressed
Main benefit of SSB:
Narrower bandwidth and more efficient spectrum use
Which sideband is most commonly used?
USB
Each sideband contains all of the information (they're duplicates).
True
Scenario: 100 W full AM. Power in the carrier?
66.67 W
Scenario: 100 W full AM. Power in EACH sideband?
16.67 W
Scenario: 100 W SSB (PEP). Power in the single sideband?
100 W
PM is a key component of digital schemes used in…
Wi-Fi, GSM and satellite TV
Digital modulation advantages:
More bandwidth-efficient and more noise-resistant
Which digital mode varies AMPLITUDE to represent bits?
ASK
Which digital mode shifts FREQUENCY to represent bits?
FSK
Which digital mode shifts PHASE (timing) to represent bits?
PSK
In ASK, carrier present = ____ and carrier absent = ____.
1; 0
Which digital mode is very similar to AM and sensitive to noise?
ASK
Which digital mode is commonly used over optical fiber?
ASK
Which digital mode keeps amplitude constant and works well at minimal power?
FSK
Scenario: a remote-control fob turns a carrier on and off to send bits.
ASK
Scenario: a link sends 1s on 1200 Hz and 0s on 2200 Hz.
FSK
Scenario: a link flips the carrier 180° to signal a bit change.
PSK
Scenario: a long-range HF voice net wants the most efficient use of power and spectrum.
SSB (USB)
Practice this module
Continue with a Physics & RF game. Choose this module in games that offer module selection.