2004 KØS, Kurt N. Sterba Strange Antenna Challenge

Operated by Erik Weaver nØew and Dwayne Walker wb5plj,

Loadlock Vertical

Icom-706MKiiG / Icom-746, 100-Watts, MFJ-962D Versa Tuner III, Generator Power
May 30, 2004

   We used this loadlock vertical for an hour or so on Saturday. When we saw a flash of lightning we quickly broke down the station and hid indoors! This was the only flash of lightning we actually saw here all weekend, although there were threatening storm fronts very close to us off and on over the course of the entire weekend.

   The step ladder to which this antenna is attached is made of fiberglass. The Altoid's mint can breakout box has one wire hose clamped to the chain-link fence and the other hose clamped to the base of the loadlock vertical. The loadlock is attached to the center conductor of the coax and the fence to the coax shielding (both via the breakout box and a short length of # stranded 12 wire). The coax is 100-feet of new RG-58. There are 10 turns of coax wrapped snuggly around a plastic jar of coffee (sans coffee, long ago poured down my caffeine hole). This is the normal hookup method used throughout the weekend.

   We only operated this antenna for about 1/2 hour before the storm rolled into Springfield. In this short time we managed to log 5 contacts ranging from North Carolina and Virginia, up to Michigan, and west to Colorado.

   All day Saturday, when we could operate between storm fronts, the bands were in pretty bad shape. High noise levels on the order of S7 and S8 (lowest dips to S5) and constant lightning crashes taking out all weak signals, and even moderately strong signals. Tough working conditions!

   These next three images provide a good idea of the neighborhood fence which served as our ground plane for both this antenna as well as the chicken wire semi-vertical. Of course, using a large chain link fence as a ground plane is nothing new. I know of a number of hams that use these as ground planes for commercial vertical antennas, such as the Butternut. They offer quite a bit of metal and work very well as ground planes. This is something to look for if you ever have to create a make-shift antenna. Search your surroundings for something like this, and if available, you are half-way home!

   In the last two images of the fence you can see the hose clamp which is securing the breakout wire to the fence rail. As normal, the end of the # 12 wire is sandwiched between the metal rail and the hose clamp (after the end of the wire is striped of insulation for 1/2 to 3/4 of an inch, of course).

 
 

   This yellow rope was CHEAP! As in "nearly useless" and NOT a deal. It broke three times while trying to get the loadlock dipole suspend from the tree branch. This is why there is so much of the next-to-useless stuff holding the loadlock to the ladder. I was just going to cut it off and throw it away anyway. I'm certain one turn would've held the loadlock in place, so this is certainly over-kill. With the winds being so high it would have been a good idea to tie it to the fence rail, but we both forgot and it never got any worse than a little wobble.

   In the next image you can catch a glimpse of the red lid to the coffee jar. This is what the coax choke is wound upon. The purpose of having 10 or so turns of coax lapped one against the other is to stop any "third path" of RF energy from flowing along the outside of the coax shielding.

   Because this coax choke was only going to be used for the weekend we only wrapped it hand-tight onto the plastic coffee jar and them held it in place with a few turns of masking tape. Dwayne has one at his house that has held up for several years now. He wound the coax onto a 2 liter plastic jug of pop, and then secured the coax with electrical tape. He did this in such a manner he could then slip the coax off his (as yet still full of pop) 2 liter bottle. Once the coax choke was off the bottle he wrapped, and wrapped, and wrapped, until he had a full roll of (blue) electrical tape wound over the and around the coax turns. (He fell onto a sale at Home Depot where he bought 20 rolls of colored electrical tape for $20, so he felt tape-rich!)

   This concept is discussed in greater detail in my "K0S Field Manual" as well in the section discussing the connections we used when wiring up these strange antennas. There is also discussion of this concept in the "ARRL Antenna Book" and "Reflections II" by Maxwell, W2DU (a great book and highly recommended, even if it'll take those us who are not engineers several readings to complete).

   You can see we just sat the rubber foot of the loadlock on one of the support braces for the step ladder. Since I had so much of this trashy rope I used far more than needed to secure the foot to the brace. Really, the weight would have likely held it in place. I would still recommend a "safety" rope, or duck tape, to secure things like this -- just to be on the safe side!

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.

   Low SWR alone, does NOT a good antenna make!

   What about the resistance? Values range from 26- to 46-Ohms, with 46-Ohms falling inside both the 10-meter and 6-meter bands. Reactance values range from 8- to 57-Ohms. All in all, pretty decent figures. I would expect this antenna to have worked very well on both 10- and 6-meters. Unfortunately, neither of these bands were open when I called CQ.

   Even on 30- and 40-meters this is a marginal antenna, but note the resistance has fallen off quite a bit by the time we reach 40-meters. This means we are losing effective radiation, and by 160-meters it is looking rather bleak. Of course, many automobile antennas are not much better, so we could still expect to make some contacts, but we'd have to work harder and miss out on some of the otherwise marginal ones.

   One of the bigger lessons to take from this is to remember to measure your impedance and do not rely only upon SWR to determine the effectiveness of your antenna. As many others have said before me, a dummy load displays a great SWR, but this does not mean it makes an excellent antenna! (Although contacts have been logged using a dummy load!)