Chapter 3: Introduction

This chapter discusses two topics that will come up time and again while planning your WISP: path loss (how far can my signal go?), and link budget (what devices can I use for this link?).

Chapters 1 and 2 have given the reader a solid understanding of how radio works, and the encoding rates that can be achieved with different radio technologies. Links providing hundreds of megabits per second can be provided, and – given a friendly radio environment – can reasonably be expected to provide throughput matching wired broadband solutions. What chapter 1 and 2 did not cover is distance. How far can one expect to send this data? What types of antenna are required to do so? This chapter seeks to answer that question. It starts by introducing the concept of “path loss” – that is, signal strength degradation over distance. It then builds this into the concept of a “link budget” – combine the elements that make up a radio link, compare with vendor data-sheets, and estimate the likelihood that a link can work.

This chapter is intended to be used in conjunction with the worksheet in Appendix 3 (see page 2). Link budget calculation is a task that most WISPs will perform regularly, either by hand or with automated tools to assist.

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