Editing Antenna System (section)

== How the antenna affects the link ==
What reaches a receiver depends on the antenna gain in the exact direction and elevation of the path, minus feedline loss, mismatch loss and any protection foldback, at both ends of the link. Consequences:

* '''Takeoff angle matters as much as gain.''' Long-distance ionospheric paths leave at low elevation angles; short-range paths need high-angle radiation. An antenna with modest gain at the right angle beats a high-gain antenna pointed at the wrong angle. See [[Propagation Basics]].
* '''Directional antennas must be aimed.''' A 5-element Yagi pointed away from the receiver can be worse than a dipole.
* '''Polarization matters.''' Ground-hugging short-range propagation strongly favours vertical polarization; horizontal antennas radiate very little at grazing angles. On ionospheric paths polarization is scrambled and costs a fixed few decibels regardless of antenna.
* '''Height shapes the pattern.''' Raising a horizontal antenna lowers its main lobe. As a rule of thumb, half a wavelength of height gives a useful low-angle lobe.