2004 KØS, Kurt N. Sterba Strange Antenna Challenge

Operated by Erik Weaver nØew and Dwayne Walker wb5plj,

Chicken Wire Semi-Vertical

Icom-706MKiiG, 100-Watts, MFJ-962D Versa Tuner III, Generator Power
May 30-31, 2004

   This was our most successful strange antenna this year. The storms had cleared and the bands were very quiet and pleasant to work, although fading was still present. And work them we did! We worked 40-meters, 20-meters, 17-meters, and 15-meters. In all, 45 contacts and QSO's across 23 states. We tried calling CQ on 10- and 6-meters, but they were not open. The only HF bands we did not try were 12- and 160-meters. Pretty good for a 24-foot piece of chicken wire and chain link fence!

   17-meters was open and I worked one station before it occurred to me that 12- and 17-meters were off limit, but before I was able to swing off to another band I was called by another station who had heard my first 11 minute QSO. Naturally I worked him and then moved to another band. That band was 15-meters, which I worked for the rest of the event. (Ooops!)

   As some of you may have noted 15-meters was not listed as a "legal" band for this contest, so the points from that band do not count as contest points, and of course the same is also true of the 17-meter QSO's. Oh well, it was a lot of fun and I enjoyed a number of interesting QSO's including the one with kj4rb who ended up going down into his basement and hooking up his shop lights as a Strange Antenna!

   I can understand not working 12- and 17-meters so there exist a refuge for those that do not like hearing contests. I am not certain the K0S "contest," which is designed to hold QSO's with others and compare antennas, is really a contest in the hard-core meaning of that term. Basically we call it a contest because we are counting contacts and a number of awards are available should anyone running their own K0S station care to apply for them. Somehow, I don't think many contesters would spend 11 minutes with one contact.

   As some of you may have noted 15-meters was not listed as a "legal" band for this contest, so the points from that band do not count as contest points, and of course the same is also true of the 17-meter QSO's. Oh well, it was a lot of fun and I enjoyed a number of interesting QSO's including the one with kj4rb who ended up going down into his basement and hooking up his shop lights as a Strange Antenna!

   Next year 15-meters will certainly be considered a "legal" band. The jury is still out on 12- and 17-meters. The opinion of any readers, K0S participants, and especially of the denizens of either of these bands would be greatly appreciated.

   Returning to the specifics of the semi-vertical...

   For this antenna we took the 24-foot roll of chicken wire, 1 inch mesh, rolled it into a long tube of wire which was held together by a series of plastic zip-ties along the seem. We then suspended one end from a tree. The other end served as the antenna feed point and the neighborhood chain link fence served as the ground plane. This connection was made at the point where the three lengths of fence were stretched to the post. This should provide a very good connection point for the "take off" (or "mirror image" as it is sometimes called). The end pointing upwards was facing very close to due east and at approximately a 30-degree angle, and was connected to the coax's center conductor.

   The pavilion from which we operated is visible under the large tree in the image along the left side of the page. This is an "Easy Up" design and has proven to be quite durable. I would recommend that you always guy your shelter. The previous weekend Dwayne and I were working a public service event (we set up in the middle of a river in the Mark Twain National Forest - very pretty!), and since it was a mild day we hadn't guyed the pavilion. Suddenly came a gust of wind that took the pavilion and hurled it 15-feet away taking our 2-meter antenna mounted to one of its legs, and knocking over the table which spilled the transceivers. We caught the 706 before any evil was worked upon it, but the 2-meter transceiver (housed inside an ammo can, as discussed elsewhere on this web page) went for a big spill! Fortunately the combination of it being a mobile rig and designed to survive an occasional bump, and the heavy case of the ammo can sheltered it from damage. However, we now guy the pavilion, even in mild weather!

   The plastic coffee jar (red lid) with ten turns of RG-58 taped to it is visible at bottom of image to the left. This serves as the coax choke that keeps any stray RF from leaking onto the outside of the coax's shielding. 100-feet of coax was used to connect the transceiver to the antenna. The coax connects to a MFJ-962D transmatch (antenna tuner), which is attached to an Icom 706MKiiG. We ran 100-watts on generator power.

   You can see the white "dog bone" insulator hose clamped to the chicken wire. The breakout wire (# 12 stranded copper) is sandwiched between the chicken wire and plastic dog bone. Hand tightening it with the hose clamp makes the electrical connection between the chicken wire and center conductor of the coax (via the Altoid's breakout box, which has a SO-239 mounted to it which is connected to a binding post, from which the # 12 breakout wire is connected to the strange antenna being used).

   The entire weekend we ran on backup emergency power, either on the battery or the gasoline generator. When running a generator it is pretty obvious when you lose power - it suddenly gets very quiet, including the transceiver! Battery power will first show less than 100% transmit power, even with the equipment set for full output. For example, we saw this affect when operating the truck dipole. We had been telling people we were running 100-watts, but over the course of operating that station the battery voltage dropped enough we were transmitting with about 62-watts (according to my Bird Wattmeter).

   The last picture of the semi-vertical shows a rope disappearing into the tree. This rope held up the raised end of the chicken wire. You can also see the stick I placed inside the chicken wire tube to help hold it open and to which the rope is attached. Hidden by the leaves, the rope was tossed over an accessible tree limb, the end of the chicken wire antenna hauled upwards, and then we ran the rope to a nearby tree and wrapped around many, many times (we had lotsa rope left over!), so many times in fact we didn't have to tie off the rope. We just tucked the free end into the coils around the tree trunk.

   As you can see from the SWR chart below, this antenna displays a pretty nice looking SWR curve (at least as compared to other strange antennas used during this event - many are rather ugly when compared to a "real" antenna). However, at 160- and 80-meters the SWR does start a distinct rise. But how much of this is "low SWR for the wrong reason" (Maxwell, W2DU)?

   SWR is not an isolated event. Transmission line loss along with resistance and reactance must also be considered. Remember that a dummy load displays a great SWR value, but it does not make a very good antenna.

   The notes along the bottom of the SWR chart show series resistance (Rs) and series reactance (Xs). In some cases I have also noted the frequency of measurement (for example 7.225, 69, 14). All of these measurements were taken with my MFJ-269 Antenna Analyzer.

Please note of the little gray boxes adjacent to the 5:1 SWR line. These indicate the approximate location of the amateur radio bands from 160- to 6-meters. This allows us to gain an impression of how each antenna shapes up across the entire HF range in which our amateur radio bands reside.

   40-meters is especially nice. Not only is the SWR 1.5, but the series resistance is 69-Ohms and there is very little reactance present (14-Ohms). Reactance is energy caught in a "loop" and unable to perform any useful work (generating our desired RF signal). It is very real energy, but it is not useful to us and this is one of the reasons why we do our best to eliminate it from our antenna systems. It is interesting to note that the bands on either side of the 40-meter "sweet spot" are actually rather bad from the perspective of resistance and reactance. At 30-meters the resistance is nearly 130-Ohms, and on 80- and 160-meters very little resistance exists.

   I fully expect we could tune up this antenna, but with so little resistance and/or so much reactance at 80- and 160-meters, we would still suffer a loss of RF radiation (which we obviously wish to maximize) when compared to one of the better bands, such as 40-meters, where this antenna should actually have worked pretty well. For example, at 15-meters it displays zero reactance. While the resistance is a little low (an optimal vertical is expected to measure close to 36- to 37-Ohms resistance, and we are measuring 27-Ohms), this should (and did) present a very easy to tune antenna. There simply wasn't not much work the transmatch had to perform in order to present the transceiver with a non-reactive 50-Ohms load.

   We didn't take any measurements of transmatch efficiency, but I would expect that both 40- and 15-meters would show less loss in the transmatch than when the transmatch was tuned on either 80- or 160-meters. Maybe next year we'll make these kinds of measurements, if we have pleasant weather during the weekend.