619 Radio Propagation and Link Budgets

619.1 Overview

This comprehensive guide to radio propagation and link budgets has been organized into focused chapters for easier learning. Each chapter covers a specific aspect of wireless signal behavior with worked examples, knowledge checks, and practical deployment guidance.

Time: ~60 min total | Difficulty: Intermediate | P07.C15.U05

619.2 Learning Objectives

By the end of this module, you will be able to:

Calculate free space path loss (FSPL) for various frequencies and distances
Apply log-distance path loss models for different environments
Quantify signal attenuation through building materials
Estimate distance from RSSI for localization applications
Design wireless links using link budget calculations
Understand Fresnel zone requirements for reliable outdoor deployments
Estimate coverage areas for Wi-Fi, LoRa, BLE, and other protocols

619.3 Chapter Guide

Chapter	Description	Difficulty
Free Space Path Loss	FSPL formula, log-distance model, path loss exponents, worked examples	Intermediate
Material Attenuation and RSSI	Building material losses, frequency dependence, RSSI localization	Intermediate
Link Budget and Coverage	Complete link budget calculations, protocol comparisons, BLE/LoRa deployment	Intermediate
Fresnel Zones and Deployment	Fresnel clearance, antenna height, ground sensors, practical examples	Intermediate

619.4 Recommended Learning Path

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graph LR
    A["Free Space<br/>Path Loss"] --> B["Material<br/>Attenuation"]
    B --> C["Link Budget<br/>Calculation"]
    C --> D["Fresnel Zones<br/>& Deployment"]
    D --> E["Knowledge<br/>Checks"]

    style A fill:#16A085,stroke:#2C3E50,color:#fff
    style B fill:#16A085,stroke:#2C3E50,color:#fff
    style C fill:#16A085,stroke:#2C3E50,color:#fff
    style D fill:#16A085,stroke:#2C3E50,color:#fff
    style E fill:#E67E22,stroke:#2C3E50,color:#fff

Figure 619.1: Recommended learning path through the Radio Propagation module

{fig-alt=“Learning path diagram showing progression from Free Space Path Loss through Material Attenuation, Link Budget Calculation, Fresnel Zones, to Knowledge Checks”}

619.5 Key Takeaways

Free Space Path Loss (FSPL) is the baseline: Real-world losses are ALWAYS worse than FSPL due to obstacles, multipath, and interference
Path loss exponent (n) determines environment impact: Indoor (n=3-4) degrades signals much faster than outdoor (n=2-2.5)
Material attenuation is cumulative: Each wall, floor, or metal obstacle adds 3-20 dB loss, drastically reducing range
Link budget calculation predicts success: If P_RX > P_sensitivity, link works. Always include 10-20 dB fade margin for reliability
Lower frequencies penetrate better: 915 MHz LoRa penetrates buildings 40% better than 2.4 GHz Wi-Fi, explaining superior indoor range
RSSI-based localization has 2-5m error: Good for room-level positioning, not precision tracking
Urban vs rural range differs by 5-10x: Same LoRa hardware achieves 15 km rural vs 2 km urban due to path loss exponent differences
Fresnel zones require 60% clearance: At least 60% of the first Fresnel zone must be clear for reliable wireless links
Ground-mounted sensors have poor range: Without elevation, Fresnel zone blockage causes 15-25 dB loss, reducing range by 80-90%
Antenna height scales with distance and wavelength: LoRa at 5 km needs 15m height, Wi-Fi at 1 km needs 4-5m height for optimal performance

619.6 Prerequisites

Before starting this module, you should be familiar with:

Networking Basics: Fundamental networking concepts
Basic mathematics: Logarithms, decibels (dB), and unit conversions