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Update for 12-11-21 13:00

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Tyler Perkins 2021-11-12 13:00:01 -05:00
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29
tech/Antenna.wiki
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@ -1,5 +1,7 @@
= Antenna = = Antenna =
See [[#Antenna Types]]
An antenna is some type of conductor, used to propagate radio signals. This is 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. done because an electric current in metal induces an electromagnetic field.
This can be transmitted and received by an antenna. When the antenna receives 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 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.

12
tech/SWR.wiki
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@ -12,3 +12,15 @@ 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, 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 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