RF Wireless Characteristics

What this chapter covers

This chapter explains the radio physics behind every wireless design.

It starts with the spectrum and the decibel scale, then looks at antennas and how a signal behaves in a real building. It finishes with the planning work that turns that theory into a layout of access points.

The chapter has five syllabus topics, grouped into four pages. Later chapters on regulation, surveys and CAPsMAN rely on these ideas, so it is worth being comfortable with them first. The environment topic and the roaming topic share a page, because interference and roaming problems often look alike.

How the topics fit together

The pages move from the signal itself to the design that uses it.

You need the decibel scale to understand antenna gain. You need antenna patterns to predict coverage. You need to know how walls and other radios affect the signal before you can place access points sensibly.

• Spectrum and decibels give you the units and the band and channel basics.
• Antenna theory explains gain, beamwidth, polarisation and the choice of antenna type.
• Environment, roaming and interference covers what changes a signal and how clients move between access points.
• Access point planning brings the earlier pages together into coverage and capacity decisions.

How to use these pages

Each topic page has the same shape, so you can skim for what you need.

• What it is: the idea in plain words.
• How it works: the mechanism, with diagrams and example commands.
• What to remember for the exam: the facts to memorise.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

Read the pages in order, because later pages reuse the earlier terms. The first page gives you the units, the second gives you the shapes of coverage, the third gives you the problems, and the fourth gives you the plan.

Work the dB examples by hand before you look at the answers. If you have a MikroTik radio, run the scan and monitor commands to see real noise and signal values.

Practice checklist for the class setup and the Module 2 laboratory

These steps use the legacy wireless package (RouterOS v6).

1. Start from the default configuration (/system reset-configuration) and make sure you can reach the router by IP address.
2. Set the country on the wireless interface, enable it with disabled=no, and check it with /interface wireless print.
3. Run /interface wireless scan wlan1 and note the networks, channels and signals.
4. Run /interface wireless monitor wlan1 and read the frequency and the noise floor.
5. Work out the EIRP from the transmit power and the antenna gain, then change the channel and tx-power (with tx-power-mode=all-rates-fixed) and watch the client signal in /interface wireless registration-table print.