Physics & RF
B12 Signals & Waves — Study Guide
This guide covers Signals & Waves 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 |
|---|---|
| AM | Amplitude Modulation |
| FM | Frequency Modulation |
| PM | Phase Modulation |
| FFT | Fast Fourier Transform |
| Hz | Hertz — cycles per second |
| |A| | Amplitude (absolute value) |
| εr | Relative permittivity |
| VROD | Vehicle-Mounted Remote Operated Direction-finding |
Key facts
What does λ (lambda) stand for?
Wavelength
An analog signal is…
continuous — its shape carries the information
A digital signal is…
discrete (often binary) — the pattern carries the information
Which is easier to intercept?
Analog
Which is more noise tolerant thanks to error correction and harder to jam without keys?
Digital
Scenario: a modern drone link sending encrypted symbols with error correction is…
digital
Which travels farther via ground wave / ionospheric refraction?
Lower frequencies (e.g., AM)
Oscillation is…
a repeating change in voltage or current above and below a reference level
What converts oscillating current into a propagating EM wave?
An antenna
One complete repetition of a wave's oscillation:
cycle
Number of cycles per second:
frequency
Distance between two consecutive peaks:
wavelength
Maximum height of a wave from its midline:
amplitude
Time for one complete cycle:
period
Where the wave is on its 0–360° circle relative to a reference:
phase
Range of frequencies a signal occupies:
bandwidth
The unit of a cycle is…
dimensionless — it's one complete repetition
Wave equation from the slides:
v = fλ
Period formula:
T = 1 / f
Amplitude is directly related to…
the signal's power
Peak amplitude is measured from…
the midline to the peak (or trough)
Peak-to-peak amplitude is measured from…
maximum positive to maximum negative
Scenario: a radio runs at 100 MHz. How many cycles per second?
100 million
Scenario: an operating frequency of 45 MHz completes how many cycles per second?
45,000,000
Scenario: a signal centered at 100 MHz spans 99–101 MHz. Bandwidth?
2 MHz
Scenario: a signal has a frequency of 1 kHz. Its period is…
1 ms
Scenario: a 300 MHz wave in free space. Wavelength?
1 m
Scenario: a 30 MHz wave in free space. Wavelength?
10 m
Scenario: a 3 GHz wave in free space. Wavelength?
10 cm
Speed of radio waves in a vacuum:
3 × 10⁸ m/s
Medium where RF travels almost exactly as fast as in vacuum (εr ≈ 1.0006):
Air
Distilled water's relative permittivity (≈80) makes RF travel about…
3.35 × 10⁷ m/s — far slower
Which medium greatly ATTENUATES RF due to high ionic conductivity?
Saltwater
Glass relative permittivity:
≈ 4–10
Dry soil relative permittivity:
≈ 3–5
Dry wood relative permittivity:
≈ 2–6
Rubber relative permittivity (used as insulator):
≈ 2.5–3.5
Higher relative permittivity means waves travel…
slower
Time domain shows…
amplitude vs time
Frequency domain shows…
amplitude/power vs frequency
Tool for the time domain:
Oscilloscope
Tool for the frequency domain:
Spectrum analyzer
Scenario: you want to see every emitter in a band side-by-side as spikes. Which domain/tool?
Frequency domain on a spectrum analyzer
An FFT converts…
time-domain samples into frequency components
Analogy for an FFT:
Turning a sound wave into its musical notes
FFT tradeoff: if it doesn't sample fast enough, it may miss…
fast frequency hoppers
VROD systems are used in EW to…
identify, classify and geolocate adversary emitters
Why is a backpack system still called VROD?
For training, documentation and logistics continuity
Practice this module
Continue with a Physics & RF game. Choose this module in games that offer module selection.