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Thursday, March 13, 2014

Simple Ham Radio Antennas: "The Poor Man's Beverage" Antenna. Post #265

Like many amateur radio operators, I've collected many boxes of electronic parts, various lengths of coaxial cable, and assorted rigs over the past 38 years.  I suppose my "shack" is testament to my "pack rat" tendencies.  I rationalize this collective habit by saying all of this material will become useful some day.  That some day was Thursday, 13 March 2014.  I had several lengths of RG-58 coaxial cable that had seen better days.  The assorted 100-ft/30.48 meters and 50-ft/15.24 meters lengths were gathering dust in the corner of the garage serving as the storeroom for my radio room.  The connectors were in good shape and the vinyl covering was intact, although a bit grey from sun exposure.  I wanted to find a use for the old cable ,now that it had been "retired" from active service.

Why not use the old coax as a low noise receiving antenna for 80 meters, which was a very noisy band even in my remodeled home in the Puna District of Hawaii Island?  About a week ago, I read several articles on what some hams call "The Poor Man's Beverage Antenna", using a length of coax between 1/2 and 1 wavelength long for the band of your choice.  The term refers loosely to the wave antenna developed by H.H. Beverage, Chester Rice, and E.W. Kellogg at the General Electric Company in the early 1920s.  Beverage published his findings in the November 1922 "QST" magazine.

Modern versions of this classic receiving antenna have been used by amateur radio operators to operate on 160 and 80 meters, bands frequently "blessed" by noise and static.

Using modified designs from GM4ULS, VE3NH, K9AY, and W9XT, I quickly made a "Poor Man's Beverage Antenna" for 80 meters.  The antenna works surprisingly well and cuts background static/ noise below that which I usually get when I use my inverted vee or doublet.

ASSEMBLY:

I designed the receive antenna for a frequency of 3.500 MHz.  Using the basic dipole formula 468/f (MHz)=L (feet) and multiplying that answer by 2 to get a full wavelength antenna for that frequency, I came up with a length of 267.42-ft/81.53 meters.  Fortunately, I had 3, 100-ft/30.48 meters of old RG-58 coaxial cable in storage.  I joined 2, 100-ft/30.48 meter lengths of coax with UHF female connectors. I then added 67.4 ft/20.54 meters of coax from another 100-ft/30.48 meter roll of RG-58 with the remaining  UHF female connector.

At the far end of the coax, I soldered the braid and tip together and covered that area with vinyl electrical tape.  Some antenna experts suggest that the far end be terminated in a resistor network to match the impedance of the coax.  Values range from 220 to 600 ohms, capable of 1 watt power dissapation.  I chose to leave the resistor network out of the system.

This antenna requires the use of an antenna transmatch or ATU.

At the ATU end of the RG-58 coax, GM4ULS recommends you "leave a gap of about an eighth of an inch in the braid.  The braid should therefore be isolated from the chassis of the ATU."  Once I did that, I connected the RG-58 to my trusty Drake MN-4 transmatch and "snaked" the coax through the shack window and laid the cable on the ground.  I ran the cable on the surface of the ground through the property's forest to a point approximately 260-ft/79.26 meters from the shack window.

I aimed the "ground-mounted" antenna towards the U.S. mainland (approximately 50 degrees from my Puna District QTH).

INITIAL RESULTS:

For the first time in many years, I was able to enjoy 80 meter signals.  Although there is some signal loss in the antenna, background noise, static crashes, and power line rfi are greatly reduced.

I will continue to use my inverted vee and doublet to transmit on 80 meters, but I will soon make a switch box to shift reception to the "Poor Man's Beverage Antenna."  On 80 meters, this antenna is definitely quieter than my other antennas.  As a bonus, the ground-mounted antenna excels as a broadcast band receive antenna.

So, don't throw away your old coax.  Make a low noise antenna instead.

REFERENCES:

http://www.gm4uls.wordpress.com/2012/06/27/the-snake-antenna.
http://www.lists.contesting.com/_cq_contest/1993-01/msg00019.html.
http://www.aytechnologies.com/TechData/ShortBev.htm.
http://isp.ca/ve3nh/snake.htm.
http://www.kc7nod.20m.com/snake.htm.
http://www.nrcdxas.org/articles/Beverage0182pdf.

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Aloha es 73 de Russ (KH6JRM).

BK29jx15--along the beautiful Hamakua Coast of Hawaii Island.
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