Thursday, December 8, 2016

Simple Ham Radio Antennas--Zip Cord Antennas--Do They Work? Post #976

Zip Cord Antennas--Do They Work?
(http://www.w1npp.org/events/2010/2010~F~1/ANTENNAS/WIRE/790303~1.PDF)
(Jerry Hall, K1TD, QST, March 1979, pp-31-32).
Author:  Jerry Hall (K1TD).  Republished by W1NPP.
Please click title link to read the full article.  ARRL members can locate the article in the "QST" archives.
Comment:

Amateur radio operators have been using lamp or "zip" cord for decades to make emergency antennas and feed lines.  Zip cord is usually 18 gauge AWG stranded copper wire, although other thicknesses are available.  Zip cord is lightweight, easy to work with, and fairly cheap.

There are really two answers to the question posed by Jerry Hall (K1TD).

First, as elements for HF wire antennas, such as dipoles, inverted vees, slopers, and verticals, zip cord does an excellent job. The plastic insulation provides some weather protection, and the cord can be "zipped" apart to form two antenna elements with one piece of parallel wire.  Some of my earliest HF antennas were made from ordinary lamp cord bought at Ace Hardware years ago.

Second, as a balanced transmission line, zip cord has significant line loss for frequencies above 7 MHz.  In his article, Hall describes a series of tests conducted with zip cord at ARRL Headquarters in 1979.  His graphs and SWR data are quite revealing.  For frequencies in the 80 meter to 40 meter range, zip cord does an acceptable job of delivering power to an antenna, with SWR topping off around 2.6:1 for 40 meters.  An antenna transmatch (i.e."tuner") can help reduce SWR a bit further.  The real problem occurs at frequencies above 14 MHz where line losses can be significant.

According to Hall, zip cord should only be used as a transmission line for operations below 14 MHz.  As antenna elements, zip cord is certainly an inexpensive option.  Of course, in an emergency, zip cord can be used as both a transmission line and as antenna elements.  If you have some zip cord at your shack, why not build a zip cord antenna and conduct a few experiments?  You may be surprised at how good it is.
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Aloha es 73 de Russ (KH6JRM).