Tämä teksti pätee kaikille taajuuksille, myös 27 Mhz:lle:
Tikapuuantenni on päästäsyötetty taittodipoli, joten suuntaavuus käsittääkseni kuten (taitto)dipolilla.
Dipoles have an omnidirectional radiation pattern, shaped like a toroid (doughnut) symmetrical about the axis of the dipole. The radiation is maximum at right angles to the dipole, dropping off to zero on the antenna's axis.
Radiation pattern of a half-wave dipole antenna. The scale is linear.
Source:
http://en.wikipedia.org/wiki/Dipole_antenna
Lontooksi se on Slim Jim. Eikä ole mikään kovin uusi keksintö...
Let me start by saying that since discovering the slim jim antenna design I have really come to respect these antennas. The design uses a matching system like a j-pole antenna. This is called the j integrated match (jim) the antenna itself is very slim hence the name Slim Jim. Designs for these antennas date back to the early 1930's the best I can tell. I have found them in QST magazine as far back as the 1940's.
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The basic Slim Jim is an end fed folded dipole. It has a radiation pattern peaking between 5 and 8 degrees above the horizon. It is this and this alone that makes this one of the best terrestrial communications antennas I have ever seen for the price.
Source:
http://www.n9tax.com/Slim%20Jim%20Info.html
Impedanssi voidaan valita esim. näin, vaikka avosyötölle sopivaksi jne. Avosyöttö on häviöttömin, mutta herkkä, esim. hakkurivirtalähteestä, säteileville häiriöille...
Although the antenna is a half wave end fed, it will perform better than a half wave ground plane, due to its lower angle of radiation.
Laskuri Slim Jim:in mittoihin, käytettävän taajuuden mukaan:
http://www.m0ukd.com/Calculators/Slim_Jim/index.php