RF homemade core (old exams and basics) | Quizlet

3 influences on wireless reach & the causes and how to deal with them

Absorption (walls, furniture, terrain)

case: physical barriers block or absorb the signal

fix:

Use repeaters/extenders

Place antennas higher or in open spaces

Use mesh networks indoors

Interference (other devices, Wi-Fi, microwaves)

Cause: overlapping signals on the same or nearby frequencies

fix:

Change wifi channels or frequency bands

Use shielding or move away from noisy devices

Distance

cause: Signal weakers the further it travels (attenuation)

fix:

Increase transmit power (if allowed)

use directional antennas

Place repeaters to cover long ranges

3 types of antennas

Dipole, monopole, yagi-uda

Dipole: principle, length, application, propagation direction

principle: radiates when current flows in opposite direction on two rods

length: half wavelength (λ/2)

applications: TV, FM radio, ham radios

Propagation: omnidirectional (horizontal plane)

Monopole: principle, length, application, propagation direction

principle: like a dipole, but only one rod is used, and the ground acts like a mirror to complete the antenna

length: quarter wavelength (λ/4)

applications: car radios, mobile phones

propagation: omnidirectional (horizontal)

yagi-uda: principle, length, application, propagation direction

principle: uses a driven element with reflectors/directors to focus signal

length: elements are around λ/2

applications: TV reception, ham radio

propagation: directional (forward)

3 types of modulation

Amplitude modulation

Frequency modulation

Phase modulation

Amplitude modulation: advantages and disadvantages

Advantage

- simple to implement (requires simple transmitter and receiver)

- requires less bandwidth

disadvantage

- highly susceptible to noises

- quality of audio is poor

Frequency modulation: advantages and disadvantages

Advange:

- Better sound quality

- FM is more resilient to noise compared to AM; hence there is a significant increase in the signal to noise ratio

Disadvantage:

- Requires more bandwidth

- Transmitting and receiving equipment of FM is complex and expensive

Phase modulation: advantages and disadvantages

Advange:

High data rate possible

More resistant to certain types of interference

Disadvantage:

Complex circuitry

Harder to decode accurately

What is triangulation

determine the location of a transmitter by measuring directional signal strength from multiple known locations.

What is trilateration

using distance (or "range") from multiple transmitters to determine the location of a receiver.

Phenomena that affect radio propagation

Reflection: bounces off surfaces like buildings or water

Refraction: bends as it passes through different mediums (like air layers)

Diffraction: bends around edges and obstacles

Absorption: signal energy is lost as heat in materials (e.g. walls, trees)

Polarization: orientation of the wave; mismatch causes signal loss

Scattering: signal breaks into weaker signals in different directions (e.g. dust, rain)

WPA3 improvements over wpa2

- Forward secrecy

- Protection against password based dictionary attacks

- Stronger encryption and security protocols

What is QAM (Quadrature Amplitude Modulation)?

QAM allows more bits to be transmitted per symbol by using multiple amplitude and phase combinations. Higher-order QAM = more bits per symbol = higher data rates.

Higher QAM numbers mean more bits per symbol but require cleaner signals.

2^6=64

OFDM:

Splits data across many close, non-interfering frequencies. Fast and resists interference.

OFDMA:

Like OFDM, but splits frequencies among users. Great for many users.

SU-MIMO:

One user, multiple antennas. More speed for one device.

MU-MIMO:

Multiple users, multiple antennas. Efficient for crowded networks.

Bluejacking

Sends unsolicited Bluetooth messages to nearby devices. Usually harmless, but can cause DoS on weak hardware (overloads it).