# Lesson 2 — Spectrum &amp; Propagation

<p class="block-synopsis">Where radars live in the spectrum, how energy spreads on the way to the target and back, and the 6&nbsp;dB rules of thumb that let you reason about free-space path loss without a calculator.</p>

<div class="block-toc">
  <a class="bt-card bt-reading" href="L02_SpectrumAndPropagation_Reading.html">
    <span class="bt-kind">Reading</span>
    <h4>Spectrum &amp; Propagation</h4>
    <p>Radar bands (L–Ka), the wavelength–frequency relation, free-space path loss, antenna gain, and beamwidth.</p>
  </a>
  <a class="bt-card bt-flashcards" href="L02_Flashcards.html">
    <span class="bt-kind">Flashcards</span>
    <h4>Review deck</h4>
    <p>Key terms and relations from the lesson, in a self-test deck.</p>
  </a>
  <a class="bt-card bt-demo" href="L02_FSPLCalculator_Demo.html">
    <span class="bt-kind">Demo</span>
    <h4>Free-Space Path Loss</h4>
    <p>Sweep frequency and range, snap to radar bands, and watch the 6&nbsp;dB doubling rules in action.</p>
  </a>
  <a class="bt-card" href="L02_Preflight.html">
    <span class="bt-kind">Pre-flight</span>
    <h4>Pre-flight quiz</h4>
    <p>Pre-class check, due before the lesson. Counts toward your IP grade.</p>
  </a>
</div>
