From 002a77387c03870f28b723b761891a0b44a1cd0c Mon Sep 17 00:00:00 2001 From: Tyler Perkins Date: Fri, 12 Nov 2021 13:00:01 -0500 Subject: [PATCH] Update for 12-11-21 13:00 --- tech/Antenna.wiki | 29 +++++++++++++++++++++++++++++ tech/SWR.wiki | 14 +++++++++++++- 2 files changed, 42 insertions(+), 1 deletion(-) diff --git a/tech/Antenna.wiki b/tech/Antenna.wiki index 82268f4..5de65b9 100644 --- a/tech/Antenna.wiki +++ b/tech/Antenna.wiki @@ -1,5 +1,7 @@ = Antenna = +See [[#Antenna Types]] + An antenna is some type of conductor, used to propagate radio signals. This is done because an electric current in metal induces an electromagnetic field. This can be transmitted and received by an antenna. When the antenna receives @@ -69,4 +71,31 @@ Example: what is the power change from 5W to 10W, in dB? 10 log (10 / 5) = 10 (0.3010) = 3dB +== Antenna Types == +=== Dipole === + +A straight conductor that is half of the wavelength. Transmits in the same +orientation as the dipole (usually horizontally). The feed line is usually +along the antenna, usually the center. The radiation pattern looks like a +circular donut. + +=== Ground Planes === + +A ground plane is a single conductor with the feed point at the bottom of the +antenna. The antenna is usually a fourth of the wavelength. A metal base below +the antenna provides an electrical mirror (exactly like how mirrors work for +light). This creates the other half of the signal, allowing for the full +wavelength to be created. + +Another common length is 5/8 a wavelength, which focuses more to the horizion. + +When operating at HF bands, especially 24Mhz (12.5m), an inductor is usually +introduced into the antenna, making the antenna longer electically then it is +physically. + +*Ground plane antennas are omnidirectional when mounted parallel to the ground* + +== Yagis == + +Yagi antennas are the common house mounted antenna you see for TV. diff --git a/tech/SWR.wiki b/tech/SWR.wiki index 0e7af9c..872b4da 100644 --- a/tech/SWR.wiki +++ b/tech/SWR.wiki @@ -11,4 +11,16 @@ 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. +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