Thursday, November 3, 2016

Simple Ham Radio Antennas--Doublet Antenna. Post #941.

Doublet Antenna
Author:  AI4J.
Accessed on 04 November 2016, 04:15 hrs, UTC.
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One of the best all-around multiband HF antennas is the "Doublet".  This antenna is simple to build, easy to erect in a variety of configurations, and inexpensive.

The doublet is basically a dipole cut for the basic frequency of interest and fed with balanced feed line, such as 450 ohm ladder line, 300 ohm television twin lead, or homebrewed 600-ohm balanced line.  The balanced feed line is connected to a balanced antenna "tuner" or to a 4:1 balun/"tuner" combination and then attached to your HF transceiver with a short length of coaxial cable. This arrangement allows the doublet to cover amateur radio frequencies between 80 and 10 meters, depending on the lowest frequency selected.

In this post, AI4J outlines the advantages/disadvantages, construction practices, and modifications of this simple, effective antenna.  My back up antenna at my Hawaii Island QTH is a doublet configured as an inverted vee with the lowest frequency of use established at 3.518 MHz.  Each leg of my doublet is 66.5 feet/20.27 meters long, with the feed line consisting of 450 ohm ladder line 60 feet/18.29 meters long. The feed line is connected to a 4:1 current balun and then attached to my Drake MN-4 antenna "tuner" with 10 feet/3.04 meters of RG-8X coaxial cable.  My doublet covers all HF amateur radio frequencies between 80 meters and 10 meters.  To reach 30 meter, 18 meter, and 12 meter frequencies, I use an old MFJ-941E antenna "tuner."

If you can only have one antenna on your property, try the classic doublet antenna--you won't be disappointed.

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Aloha es 73 de Russ (KH6JRM).