vimwiki/tech/SWR.wiki

= SWR =

Standing Wave Radio (SWR) is a phenomenon where power sent down a feed line is
reflected back by the antenna. Due to this, a standing wave is formed in the
feed line.

This only occours when the impedance of the antenna and the feed line do not
match. This is often caused by having the incorrect sized antenna for the
signal.

SWR is the same as the ratio of antenna-to-feed or feedline-to-antenna
impedances, whichever is greater than 1. No reflected power is a ratio of 1,
and means that there is no interference pattern. Because [[Impedance]] changes with
frequency, the SWR also changes with frequency. 

Becuase of higher SWR means more reflected energy, a lower SWR means more of
the transmitters power actually makes it out through the antenna as a radio
wave. The power feeding back to the transmitter also creates interference with
the signal itself, which can cause voltages higher than what the transmitter is
designed for. Due to this *most equipment can only handle SWR of 2:1*.

If you expereince SWR, check

* Antenna length vs frequency
* Faulty feed lines/feed line connectors
* Erratic SWR means loose connections in feed line

== Meters ==

An SWR meter allows you to measure the power flowing to and from the antenna,
therefore calculating the amount of SWR. Another type of SWR meter is a
directional Wattmeter, determining the amount of power in each direction.

Antenna tuners exist, which alter the Impedance of the feed line to match that
of the antenna, so make the SWR 1:1. This is either manual or automatic.