Thursday, September 25, 2014

Simple Ham Radio Antennas: The Extended Double Zepp Antenna. Post #304


This historical amateur radio antenna is becoming a bit more popular these days because it delivers modest gain over a horizontal dipole (about 3 dB) and is simple to build. This video by Stan Gibilisco covers all of the basics of this antenna and its construction. While it is perhaps best to use two supporting masts for the antenna, it can work reasonably well configured as an inverted vee. According to Stan, the EDZ antenna is basically "a collinear array of two 5/8 waves in phase." So, each antenna element will be a bit longer than the dipole most of us are accustomed to building. Also, the usual dipole formula, 468/f(MHz), doesn't apply here. After consulting several texts and antenna books, I chose to use the formula 585/f(MHz) for my EDZ Antenna. My last EDZ was cut for 20 meters and it worked very well. This time around, my property is a bit larger and I thought a 40 meter EDZ configured as an inverted vee would fit within my property without being seen by the neighbors (out of sight, out of mind). Using the new formula and cutting each element for my chosen frequency of 7.088 MHz (the frequency of the Hawaii Afternoon net), I cut two pieces of #12 AWG house wire to a length of 82.53 ft/25.16 meters each. These wires would comprise each half of the inverted vee. A ground radial system is not required with this antenna. Rather than use 50 ohm coaxial cable for the feed line, I opted to use 75 ft/22.86 meters of 450 ohm ladder line as the feed line. Using a balanced feed line in conjunction with a W9INN 4:1 balun and my Drake MN-4 antenna transmatch (tuner), I could get multiband use between 40 and 10 meters with just one antenna. I built this antenna on the ground. I had a spare 33 ft/10.06 meters MFJ telescoping fiberglass mast which would support the feed line and the two antenna elements. I used a "ladder lock" device to attach the antenna elements to each leg of the ladder line. All connections were soldered and covered with several layers of vinyl electrical tape. Once the mast was raised on a wooden support stake and the drooping elements tied off at prepositioned 10 ft/3.04 meters pvc pipes, I ran the 450 ohm ladder line to the 4:1 balun attached to the garage wall. A 6 ft/1.82 meters length of RG-8X coax went from the balun to the window patch panel and from there, another 6 ft/1.82 meters of RG-8X coax went to the Drake MN-4. Shorter pieces of coax joined the Argosy II transceiver, dummy load, and low-pass filter to the Drake MN-4 antenna transmatch. Performance on 40, 20, 15, and 10 meters was good when propagation was "in". Using Stan's overall guidance, I found design and construction of this basic  antenna  simple and inexpensive. Most of the materials I had in the shack. What I didn't have, I bought at Home Depot and Ace Hardware. The antenna is a bit large, but the performance of this antenna more than compensates for its size. ----------------------------------------------------------- For the latest Amateur Radio News and events, please check out the blog sidebars. These news feeds are updated daily. Until next time, Aloha es 73 de Russ (KH6JRM).