Have you ever thought of using a pair of folding chairs as a dipole? December 2002 I sat a pair on my roof and contacted D44TD in Cape Verde, Africa, along with British Columbia, Mexico, Brazil and Costa Rica. I had a lot of fun and I was hooked!
My curiosity with strange antennas had been stirred by reading Kurt N. Sterba's three "Aerials" books (www.wr6wr.com) in which he discussed some of the unusual antennas he had used over the years, such as an umbrella and a shopping cart dipole. Disillusionment with my auto tuner was the final push needed to seek alternatives. I kept an eye on eBay, picked up a couple used MFJ-969 antenna tuner units (ATUs), and started to scheme!
To whet the appetite of fellow hams I wanted to fly a strange antenna at a club meeting. Several ATUs were inspected, and their theory and proper operation discussed. We then went outside, laid a 3x8 foot section of door screen on the asphalt, placed a few scraps of 2x4 down as insulators and upon these sat a 3x8x2 foot (WLH) dog pen using just the four sides, without the top or bottom; sans puppy. It sat 1.5 inches above the screen.
I ran 60-feet of RG-58 from the ATU, wrapped 6 side-by-side turns around a plastic coffee jar to serve as a coax choke, to an Altoids mint can into which I had previously mounted a SO-239 and pair of binding posts. The Altoids can served as the breakout box taking the coax feed to separate wires (black post to the shielding; red post to the center conductor). Inserted into each binding post was one end of #12 insulated wire, about 14 inches in length. Naturally, the wires were stripped of their insulation at each end. A plastic dog bone insulator (perfect!) was placed against one of the bars of the cage. The red wire was tightly pinched between the bar and insulator with a hose clamp. Similarly, I bunched up a corner of the screen around another dog bone, and secured it and the black wire with a second hose clamp.
I returned to my Icom 706 and tuned our "antenna" with my MFJ-969. I achieved a nearly zero reflected wave, fully loaded with 100 watts. CQ was called on 20-meters. I briefly described our club's experiment and desire to contact another station during our club meeting. With 20-odd members huddled around the rig it only took a few calls before we heard a reply, clear as the day is long from Kevin, KA2NUE. We heard him 57 and he heard us 53, which we all thought was pretty good for 1.5-inch height on a dog pen! But where was he? Across town, or several states away? We informed him we were in Springfield, Missouri, and asked his QTH. You could hear a pin drop as we awaited his location - 20 miles north of (everyone held their breath) New York City. Success!
Cheering and hand clapping drowned out his next few words. The dog pen worked and it was great fun hearing the surprise in his voice on the other end, "you're using whaaat?" We ended the meeting with a second contact, Ed, N3EYA, with whom we had solid 57 to 59 contact and intermittent QRM. That evening many of us rediscovered the joy of picking out voices at a great distance with a bit of wire and magic, or in this case a bit of dog pen and voodoo.
May 10-11, 2003, our club hosted the special event station, KØS, the Kurt N. Sterba Strange Antenna Challenge. Those who sent a SASE received an image of the strange antenna with which they were worked on their certificate. Our operating site had been selected for its visibility. Our public demonstration took place along a major street in the front lawn of a local university library. Our goals were to introduce non-hams to our hobby, gain news coverage, display an aspect of emergency preparation, rekindle the interest of inactive hams, and have a whole lot of fun!
Saturday morning the special event dawned with brutal sustained winds, forecasts of severe thunderstorms, and the threat of tornadoes. A week earlier an extremely large storm front had swept dozens of tornadoes across our part of Missouri, and leveled many homes, businesses, and a small town. Needless to say we were a little apprehensive, but "the show must go on," especially since the local newspaper planned to feature our endeavor in the Sunday edition!
By 10 A.M. we had set up two portable stations shielded by a portable pavilion that prominently displayed a "Public Welcome! www.smarc.org" banner, along with several strange antennas that were ready to fly. I had already spent some time with the press. Our reporter and photographer were ready to see if these bizarre antennas would work, as were some of the hams that had missed our club's test flight.
I tuned the shopping cart dipole (borrowed with permission) to our published frequency of 28.505 MHz. It tuned as easily as the dog pen. Unfortunately 10-meters was quite dead. It was as if there were no antenna hooked up (yes, I checked).
It was then the photographer asked how it was going (thanks Murphy!). I explained the band was "dead" and we would have to try another wavelength. I had previously briefed her on bouncing radio signals off the atmosphere and that sometimes they cut completely through it or fail to be reflected (take that Murphy). Still, I could see her doubt deepen (well - lets call it a draw).
We immediately switched to 20-meters with an A-frame vertical. One aluminum ladder had been laid on the grass. A second multi-purpose ladder, bent into an "A" isolated by 2x4s, stood over the first. The coax terminated without a choke or balun, the braid connected to the horizontal ladder, and the center conductor attached to the A-frame vertical.
The reporter peered over the operator's shoulder as he responded to a CQ. We immediately received our first contact of the special event. The reporter's jaw dropped - he was obviously surprised to discover we were talking to another ham in Bend, Oregon, with armchair copy using only ladders! The photographer snapped several pictures. We were in business and Murphy took his OSHA required coffee break.
Our reporter had been dubious up to this point, but could it just be luck? Our operator spun the dial, hunting for an open frequency to make his own. Shortly we contacted Philly, Florida, California, and Arizona twice. No, not luck, we were onto something here! As the reporter quoted me in our local newspaper, "if they had a ham-radio operator on Gilligan's Island, they wouldn't have had a show."
We employed two other configurations of ladders: a 24-foot vertical "top hat" ladder (a reference to the arms that reach out to a wall for additional support) using chicken wire as a ground plane, and a ladder dipole at 3-feet height.
Four contacts were established with the top hat vertical over a 25-minute period on 40-meters. The most interesting was a mobile station in California, but we also contacted the East Coast when North Carolina was added to the log. During what was to be the final 30-minutes of the first day we worked the ladder dipole. Virginia and Florida were logged on 20-meters. We also made a contact on 6-meters, but he was only about 15 miles from our location, which was not very exciting.
Unfortunately, we didn't have time to experiment with other antennas or test variables such as height or feed points. Murphy played his trump card: the approaching storm was in fact severe. Our local Skywarn net was activated and about half the hams on site were called to service. After less than 3 ½ hours we packed our equipment and "antennas" as the thunderstorm loomed over us. The Missouri sky was kept alight with cracks of lightning for most of the remaining day.
Sunday was a beautiful day for playing with antennas, although still quite windy. Dwayne, WB5PLJ, and I made 40 contacts over the course of 4 hours, one hour of which was spent working a nearly deaf antenna. We operated over the local noon hour and again later in the evening following visits with our respective mothers. Murphy must have also been visiting his mother, because we never heard from him.
The weapon of choice for the day was a trucker's loadlock. This is a metal device designed to keep loads stable inside a big truck's trailer. It was a little over 8-feet long, the meat of which was comprised of 1 ½ inch square steel. Three configurations were attempted; all of which tuned easily with the MFJ-969. In each case we used a coax choke, and the Altoids breakout box. The center conductor was attached to the foot of the loadlock with the shielding routed to the opposing ground element. We made no surface preparation. We simply hose clamped the wires tightly against the metal.
We began in a vertical orientation with the loadlock tied to a fiberglass stepladder with its foot about waist height. A small chain link fence served as the shielding connection. This fence had two 26-foot runs, 90 degrees to one another. We set up in the middle of one of these legs. It later occurred to me that a better placement may have been where each leg of the fence met, allowing longer runs for the returning energy (the mirror image of the vertical element). However, the 180-degree orientation of the legs may have been superior to 90-degrees. I wish I had tested this change for comparison.
I tried 10-meters first. It tuned easily but was still dead. Fortunately, 20-meters worked well. Contacts ranged from the West Coast to the East Coast, and we captured our only DX for the event - VE3DIJ in Ottawa, Canada. One of the interesting stations we contacted was K2BH, portable in North Carolina near the famous Marine Corps base. He switched from his long-wire-in-tree to a flagpole and contacted us a second time. Although the signal strength dropped he was still easily read. We worked 29 stations, QSO style, in a little under 1-½ hours.
While Dwayne visited his mother, my second attempt suspended the loadlock horizontally between a nearby tree and basketball hoop. The shielding was connected to a support arm of the backboard, which was in turn bolted to a vertical 6-inch diameter pipe. This was the "deaf" antenna. After an hour of calling CQ on 20-meters the only station to reply used a beam standing at 200-feet! This did illustrate only one station need invest in an expensive antenna system to achieve two-way communication.
The final test of the loadlock came in the closing hour of the special event. It was suspended from the same tree as the deaf antenna but with its base about one foot from a large neighborhood chain link fence, which served as the connection point for the shielding. This time the loadlock was at approximately a 30-degree angle, pointed eastward, and worked quite well. I operated 20-meters for a little less than an hour making 10 leisurely contacts from one end of the West Coast to the other. The first station was mobile beside the San Francisco Bay. He ran only 3 watts, with a nice signal.
After the final seconds of the special event ticked away only evaluation of our "antennas" remained. Why did some work, and some fail? A dead band was self-explanatory, but why did the horizontal loadlock fail?
To create an effective signal under less than ideal situations it is important to understand how energy is transferred from one part of the antenna system to the next. This allows one to assure a compromised antenna will work as well as possible. Let's begin by defining certain terms:
RF energy carries Radio Frequency signals. It is alternating electromagnetic energy made up of two waves at 90-degrees to one another. One wave is magnetic and the other is electrical.
Coax is a type of transmission line that carries the desired RF signal down a center conductor, which is surrounded by a non-conductive substance ("dielectric"), and has a metal braid/foil ("shielding") wrapped around the dielectric. The braid is grounded and serves as an electrical shield to protect the center conductor from undesired electromagnetic energy, and also serves to restrict the center conductor from radiating RF energy. Coax is "unbalanced" because the energy travelling forward in the center conductor is not equal and opposite to the energy returning along the shielding (specifically, along the inside edge of the shielding).
Ladder line (window line; twin lead) is a type of transmission line that carries the desired RF signal along two wires separated from one anther by a specific and constant distance. In one wire the energy flows toward the antenna while in the other wire it returns to the transceiver. As long as these two energy paths are opposite each other and of the same magnitude they cancel out, resulting in no radiation - they are "balanced." Ladder line generally performs best when nothing enters a diameter of two or three times the distance separating the wires, however, most critical is the first diameter.
A coax choke is a length of coax coiled tightly side-by-side (it may be helpful to roll it on a form, such as a large pop bottle, and secure it with electrical tape). Its purpose is to stop (or "choke") the flow of electrical energy travelling along the outside of the coax shielding (it doesn't affect the energy returning along the inside of the shielding). Sometimes a balun is also used for this purpose.
A balun converges a BALanced load into an UNbalanced load. It is used to connect coax and ladder line. Baluns are transformers designed to provide a certain ratio of change to the amount of energy flowing from one side of the balun to the other (typically 1:1 or 4:1). They can either be designed to transform current or voltage.
A SWR meter measures the amount of energy sent forward, toward the antenna, and the amount of energy reflected off the antenna, and returning to the radio. Both the forward and reflected energy are sine waves and the ratio of their difference remains constant along the transmission line regardless of where the measurement takes place. This is why it is called a Standing Wave Ratio, SWR. VSWR, Voltage Standing Wave Ratio, is an interchangeable term. SWR became increasingly important to amateurs as transistor-based transceivers replaced tube rigs. Transistors are more easily damaged by a large SWR difference and many have self-protection circuits that reduce power output when sensing a SWR greater than 1.5:1 or 2:1.
Impedance has more than one definition depending upon the context in which it is used. Impedance is the measurement of resistance to current in an AC circuit, having two components: pure resistance, and reactance. Impedance is also a measurement of the rate at which energy is transferred. For a power source (transceiver) to supply all of its designed power to a load (antenna) both must operate at their design impedance (rate of energy transferal).
Reactance is resistance to electrical current other than purely resistive. Reactance performs no useful work - it is energy caught in a loop. Reactance is sometimes called "imaginary" in the mathemagical sense, symbolized by "j" (as in "300 Ohm +j 25 Ohm"), but its energy is very real. The term "imaginary" only refers to the symbol appearing in formulas.
Resonance is the state of zero net reactance. Resonance of the antenna is required for optimal performance. When the antenna becomes a purely resistive load (zero reactance), it efficiently absorbs and radiates RF energy supplied to it.
An Antenna Tuning Unit (ATU) is comprised of various combinations of coils and capacitors, some of which are variable. The positions of these components are adjusted in such a way that when placed between a transceiver and antenna they cancel out reactance and transform pure resistance so that each side of the ATU simultaneously provides the proper amount of resistance to the rig and antenna. Both the rig and antenna operate at their design impedance.
A basic antenna system includes your transceiver, ATU (if used), antenna, and the transmission line connecting them. Your extended antenna system includes the earth over which it stands as well as other environmental elements such as a lead crystal ashtray against which one's ladder line is resting. Unlike glass, the lead in this crystal will cause rather strange tuning effects (not that I'd know from personal experience, hi-hi). Both an antenna's height above the earth and its distance from nearby objects affect its impedance. RF energy projects both electrical and magnetic fields. Anything interacting with these fields affect your antenna system, with nearby interactions being far more dramatic. This means an antenna tested and trimmed to measure exactly 50 ohms impedance on your worktable will likely display different impedance at 40-feet height above your house.
As you transmit, energy leaves your radio travelling toward your antenna. Along the way some energy becomes heat as it passes through the components of the radio, ATU, transmission line and finally the antenna itself. Even in a perfectly designed antenna system there will be some amount of signal loss in the form of heat (resistance). Provided your transmission line and equipment are in good repair, this heat represents only a small amount of energy in a tuned system.
However, if your transmission line is in poor condition, large losses may be experienced. Interestingly, this is sometimes seen by a SWR meter as a nearly perfect 1:1 reading. Imagine transmitting into an infinitely long piece of coax. Without an antenna and while radiating zero RF energy, you will read a perfect 1:1 SWR. This is because all the energy sent forward is absorbed as heat along the way, leaving zero energy to return to your SWR meter as reflected energy, or to radiate as RF. This problem often occurs with old, or cheap, coax ("Low SWR for the wrong reasons," Maxwell, W2DU, "Reflections II"). If there are cracks in the coax cover, or connectors, moisture will seep inside and short the shielding to the center conductor, defeating the dielectric. Partially broken conductors (center or braid) may cause erratic signal strength or pops or crackling to be heard. Typically these problems show as high or erratic SWR. When you first install your antenna system you should measure the SWR, and record it. Periodically measure your SWR, seeking SWR changes. Either increased or decreased SWR indicates potential trouble (remember to account for the accuracy of your measuring device - changes within its error range should be ignored).
Assuming your transmission line and other equipment is in proper operating condition we are left with only one problem: attaining a proper impedance match between the transceiver and the antenna.
It may be helpful to think of impedance as two entwined types of energy, each of which must be properly dealt with in order to present your rig and antenna their proper impedance (rate of energy transfer). The first is reactive energy - energy caught in loops. The second is purely resistive energy. Both reactance and pure resistance are measured in ohms. Reactive energy performs no useful work. Resistive energy performs the work of carrying your RF signal along the transmission line between rig and antenna, ultimately radiating as radio waves.
To develop full power your transceiver must see its design impedance as it looks into the transmission line toward the antenna. In turn, each antenna also requires specific impedance to efficiently operate as it looks back toward your rig. Your rig and antenna often require different impedance. When your rig and antenna each observe their design impedance with zero reactance, your antenna system is matched ("tuned"), the antenna is resonate, and you will produce maximum effective power.
This "tuned" condition is normally achieved by inserting some means of impedance matching between the transceiver and antenna. It is possible to design a resonate antenna without inserting a matching mechanism however, the antenna will only operate across a small frequency range. Most amateurs desire to operate wide frequency ranges, and often across multiple bands, which requires either multiple antennas or the ability to tune one antenna across multiple bands. Multi-band tuning is commonly accomplished with an ATU.
As you transmit, RF energy leaves your rig at 50 ohms impedance and zero reactance. This RF is altered to some degree by the transmission line, and arrives at the antenna (almost certainly) displaying impedance other than what the antenna requires for optimal performance. Some energy will now be "reflected" from the antenna back toward the transceiver (because the antenna can only fully absorb energy that matches its impedance). Reflected RF energy travels along the transmission line, is again altered, and returns to your radio with impedance other than 50 ohms pure resistance along with some amount of reactance.
If the rig has a self-protection circuit its power output is reduced. The reflected wave is re-reflected towards the antenna along with some added power from the transceiver. This process repeats. Your maximum power output is reduced, some energy is reflected and re-reflected between the transceiver and antenna until it is either radiated from the antenna or escapes from the transmission line as heat. Transmission line loss (heat) can not be reduced, except by using a higher quality line (less heat is generated), reducing the amount of energy reflected from the antenna (each time the RF travels along the line, loss occurs, therefore fewer trips equals lower line loss), or both.
The goal when using an ATU is to "tune" the antenna so it receives RF energy at the rate (impedance) for which it is designed and to simultaneously present the transceiver with the impedance for which it is designed. Inserting, and tuning, an ATU between the rig and antenna allows one to adjust (transform) two forms of energy: reactance and pure resistance, which together form (resistive) impedance. (Remember "impedance" refers to one of two things, depending upon context - the rate of energy transfer, or electrical resistance comprised of reactance and pure resistance.)
Let's first address reactance. Imagine a magnetic field generated by an alternating current. As energy flows forward a magnetic field develops. When energy flows in the opposite direction the magnetic field changes polarity, handing energy contained in the first side of the magnetic field to the other side. As the current continues to alternate, this magnetic energy is handed back and forth. The energy is real, but only oscillates between two alternating poles of the magnet, performing no useful work. Reactance found in your antenna system can be inductive or capacitive, and its magnitude is affected by the impedance differences present in your antenna system. It should be obvious that minimal reactance is desired because when reactance is zero, all energy present performs useful work - radiating RF (ignoring line and component loss (heat) for the moment).
The ATU removes reactance from the antenna system by adding an equal magnitude, but opposite sign (+ is inductive; - is capacitive) of reactance, to the reactance already present in the system. For example, if +j 225 ohms exists, the ATU will insert -j 225 ohms reactance into the antenna system. The result is a total cancellation of the reactance, eliminating all energy caught in non-productive loops. This process leaves only pure resistance in the antenna system.
As an example, let's pretend your antenna at 40-feet displays 300 ohms impedance (recalling our ATU has already cancelled reactance), but is designed to receive energy at 60 ohms impedance. Your final adjustment of the ATU will cause pure resistance to be transformed (added or subtracted) from the antenna system so that the transceiver sees 50 ohms impedance while the antenna simultaneously sees 60 ohms impedance. With this last adjustment our ATU has brought the antenna into resonance - it experiences the state of zero reactance. When you transmit 100 watts output, the antenna will radiate 100 watts power (less heat losses, of course, the laws of conservation of energy still persist).
Expressed symbolically, where Iant = Impedance of the antenna, Itx = Impedance of the transceiver, and Iatu = Impedance of the matching unit, the first condition is:
Itx [is not equal to] Iant
This unequal condition is altered by inserting an ATU (Iatu). As a result of adding (or subtracting) reactance and pure resistance to both the transceiver and antenna, each is provided their design impedance:
Itx ± Iatu = Iant
Only one potential problem remains. A properly designed antenna presents two paths of energy to the transmission line. In the case of a coaxial feed, one path flows along the outside of the center conductor and the other along the inside of the shielding. If the antenna is not properly designed a third leg of energy may exist flowing toward the transceiver along the outside of the coax shielding. The presence of this undesirable, and unpredictable, third leg of energy can create problems such as stray RF. It will also make most SWR meters unreliable - they are designed to measure the expected two legs of energy, not three. Fortunately this extraneous energy can often be stopped simply by using a coax choke or balun.
Formulas and a plethora of plans exist to properly design "normal" antennas so they present a balanced load to the transmission line (two legs of energy). However, the odds our dog kennels, ladders, and load locks provide a properly balanced load to the transmission line is very low. While I think using a coax choke or balun is sensible in any case, I feel it is imperative when experimenting with "strange" antennas - elimination of known problems is logical.
Key concepts to remember:
This was our club's first Strange Antenna Challenge. We didn't really know how well our makeshift antennas would work on the various bands and were concerned that we would not be able to work the longer wavelengths. It was thought 10-meters offered the best opportunity because its smaller wavelength would be easier to capture. This is why only 28.500 MHz had been listed in the special event announcements.
As it turned out 10-meters was dead. We made nearly all our contacts on 20-meters as well as a few on 40-meters and one on 6-meters. Of course, each of our strange antennas had much more surface area than a wire. I'm uncertain how this affected our loading and signal. I have not found any antenna modeling software that allows one to analyze a ladder or shopping cart. (I'd like to know where I might obtain such software, or to receive comment on this point.)
What are the chances our ladders displayed a balanced load to the feedline? Remote at best! Almost certainly the shielding carried a third leg of energy along its exterior to the SWR meter. Therefore, use of a balun, or choke, when experimenting with strange antennas is prudent. In most cases failing to employ a choke or balun should have compromised the SWR meter however, I believe the impedance transformation produced by the manual ATU should have remained accurate. Provided the antenna system remained stable (no changes in feedline impedance such ladder line blowing against a pipe, etc.), it seems logical that once the ATU is tuned, the entire system should maintain a well-matched load. This view was supported by observation of the antenna taking the full load supplied by the radio.
We worked all of our contacts barefoot with 100 watts. Each "strange antenna" easily tuned with a manual ATU and fully loaded. We did not try automatic tuners. I suspect my SGC-237 would not have performed very well under these conditions - it will not tune certain wire configurations, so I doubt its software would be able to find a proper match for a shopping cart or ladder, although to be fair, I've not tried.
Throughout the KØS special event each band demonstrated moderate fading, but the background static remained reasonably low. Stations we contacted were running anywhere from 3W to 1KW. Most ran 100 watts while their antennas ranged from multi-element beams to dipoles, verticals, and loops, usually at modest heights. Reports were generally strong, in the 55 to 59 categories. Only a few were 37 to 44, and none of these were from beams. The weakest report received when working a beam was 53, and 70% were 56 to 59. Only eight times, out of 53 contacts for the weekend, did the RS reports vary greatly, and of these 15%, 75% of the time we heard them as the weaker station. To my surprise, only 15% of the contacts were particularly difficult to make.
Recall however our "deaf" antenna was virtually useless and we can not know how many stations we were unable to hear. We had examples of antennas that performed poorly and those that performed quite well, so it is logical there are a variety of "strange" antenna designs that would prove marginal. The other station's power and antenna height would be other important aspects to consider, but since the vast majority of stations used 100 watts at modest antenna heights, I believe these conclusions to be generally accurate.
TABLE 1 ALL REPORTS (TOTAL 76) BOTH DIFFERING REPORTS SAME (TO THEM) (TO US) 56+ 19 (25.0%) 9 (11.8%) 8 (10.5%) = 47.3 % 55-44 6 (7.9%) 7 (9.2%) 12 (15.8%) = 32.9 43-41 3 (3.9%) 5 (6.6%) 2 (2.6%) = 13.1 39- 1 (1.3%) 2 (2.6%) 0 = 3.9 ? 0 0 2 (2.6%) = 2.6 (TOTAL = 99.8 %) TABLE 2 OTHER STATION ON BEAM (TOTAL 20) BOTH DIFFERING REPORTS SAME (TO THEM) (TO US) 56+ 11 (55.0%) 3 (15.0%) 0 = 70.0 % 55-44 3 (15.0%) 0 3 (15.0%) = 30.0 43-41 0 0 0 = 0 39- 0 0 0 = 0 ? 0 0 0 = 0 (TOTAL = 100.0 %) TABLE 3 OTHER STATION'S ANTENNA UNKNOWN (TOTAL 9) BOTH DIFFERING REPORTS SAME (TO THEM) (TO US) 56+ 0 1 (11.1%) 2 (22.2%) = 33.3 % 55-44 1 (11.1%) 1 (11.1%) 0 = 22.2 43-41 0 2 (22.2%) 1 (11.1%) = 33.3 39- 0 0 0 = 0 ? 0 0 1 (11.1%) = 11.1 (TOTAL = 99.9 %) TABLE 4 ALL REPORTS MINUS BEAMS AND MINUS UNKOWN (TOTAL 46) BOTH DIFFERING REPORTS SAME (TO THEM) (TO US) 56+ 8 (17.4%) 5 (10.9%) 6 (13.0%) = 41.3 % 55-44 2 (4.3%) 6 (13.0%) 9 (19.6%) = 36.9 43-41 3 (6.5%) 3 (6.5%) 1 (2.2%) = 15.2 39- 1 (2.2%) 2 (4.3%) 0 = 6.5 ? 0 0 0 = 0 (TOTAL = 99.9 %)
The above would seem to indicate several things:
Sunday the feedline, coax choke, and breakout box from coax to wire connectors were identical in all cases. This would mean the ATU had only the differences between the antennas (all the same loadlock) with which to contend.
The first and third configuration of the loadlock worked quite well. These both used chain link fences as the ground element with the base of the loadlock at waist height, nearly the same height as the fence rail. In the second arrangement the deaf loadlock was about 10-feet above the earth with a 10-foot pipe planted in the earth as the ground.
The orientation of the loadlock (considered the radiating element and fed by the center conductor) was changed in each set up. First it was used vertically, then in a horizontal position, and finally at about a 30 degree angle relative to Mother Earth. I doubt such a short radiating element's orientation could make much difference by the time it has bounced off the atmosphere and ground objects a number of times. Polarization of the signal is moot. However, because these antennas were so low a change in height above earth from three feet to ten feet may have noticeably affected the resistance relative to earth. Another difference is the path provided for the antenna's "mirror image" energy. The deaf antenna provided only 10-feet of pipe and some short supporting bars to return this energy, all of which were to one side of the radiating element. On the other hand, the fences provided a minimum of 13-feet of return path to either side of the radiating element, and in the third case much more than this.
At 14.250 MHz, a single wavelength (y) is roughly 69.07 feet (300 / 14.250 * 39.37 / 12). This means y/4 is about 17 feet 3 inches. The loadlock measured 8 feet 3 inches, which is pretty close to y/8 (8.25/69.07 = 0.12). Even multiples of y/4 are generally considered favorable to strong RF radiation whereas odd multiples are considered poor candidates. The loadlock fell almost exactly between these extremes, but was in any case a small element at only y/8. There is also the additional mass as compared to a wire to be considered. Other than expecting greater bandwidth than wire I am uncertain how this may have affected the antenna system.
I measured the natural resonate frequency (sans ATU) of these three antennas with my MFJ antenna analyzer (I neglected to record the Rs and Xs for the first antenna):
(1st) Vertical: 16.0 MHz at 1.01 SWR; (2nd) Basketball hoop: 26.9 MHz at 1.2 SWR; Rs = 42; Xs = 8; (3rd) Sloper: 16.3 MHz at 1.1 SWR; Rs = 55; Xs = 3;
I found it interesting the reactance was so low in the two cases I recorded. Both were also reasonably close to the impedance of the coax. A surprisingly good match, really, although neither was resonant in an amateur band.
All three antennas were operated close to 14.250 MHz. While 17-meters was not attempted, it seems reasonable to assume this would've worked quite well. Both 17- and 20-meters are about the same distance from the measured resonance of the first and third arrangement of the loadlock. The second antenna's natural resonance fell roughly between 10- and 12-meters, so it may have worked well had 10-meters been open.
It is possible the second attempt was just too far from its resonant frequency to be able to generate an efficient signal. I think more likely is the increased height combined with the inferior grounding elements caused the ground losses to climb to the point where efficient radiation no longer took place. (Comments are welcomed.)
Field selection of ground elements should include metal objects that offer reasonably long return paths on at least two opposing sides of the vertical element. The first and third ground elements (fences) seemed to perform much better than a single 10-foot pole set in the earth, orientated to only one side of the radiating element. Not enough test positions were measured to reach any conclusion regarding preferred orientation of either the radiating or ground elements, nor whether closely mating with Mother Earth was important.
For comparison I wanted to try a dipole but was unable to locate a second loadlock. I had planned to record measurements for all antennas, but as mentioned, the severe weather on Saturday precluded my planned tests. But there is always next year, and I've since found the other loadlock buried on my front porch!
Send out press releases discussing your activities. It is pretty simple. It only takes a little time. If you are uncertain how to format a press release you can find the one I used for this event on my web site. It is the same format I always use and it seems to have worked for me on a number of occasions.
There is an email based PR forum sponsored by the ARRL (jhagy@arrl.org) which you may find useful. Many of those contributing to this forum are either in the PR or news business and many useful ideas are presented. I post planned releases and review the group's feedback before sending it to the press, which has proved useful.
Remember shifting the focus of the news release from your club to another party can also be effective. As an example, when our ARES group served as the only means of communications for the American Red Cross during a recent tornado drill, the press release primarily discussed the Red Cross. That amateur radio is often the only form of communications following a disaster was pointed out in the resulting media coverage. One of the ham-assisted damage assessment teams was televised. So both the Red Cross and ham radio obtained good press. Furthermore, one of the Red Cross volunteers was so impressed by our communication abilities she has since obtained her ticket and joined ARES.
Spread the word about your next club meeting, picnic, hamfest, or special event station. Be sure to talk it up on your local repeaters too. This effectively reaches fellow hams as well as scanner enthusiasts. Send out those press releases. You do have an advantage in that you are a local interest. Whether as a human-interest story, or as a tie-in to national events, your local news services are always seeking a local angle. You never know when you might gain some positive press for ham radio - and we need all of that we can get!
This is always important, but even more so when in the public arena. As much as we desire press, front-page coverage due to a trip to the emergency room is not what ham radio needs! We discovered even fellow hams have children that either do not understand the hazards energized antennas present, or who will not comply with their parents wishes to remain at a safe distance. We expected this behavior from the general populace, but not fellow hams.
We did not assign one specific person to watch for the safety of others. In retrospect this would have been a very good idea. Had the antenna elements been 10 feet or higher above the ground I think this would be less critical. However, with antennas laying on the ground and at waist height, this became a real concern because all the antennas were immediately accessible to the youngest of children. More than once we ceased operation because kids were closely inspecting our strange antennas (they were pretty interesting), or actually standing on one element and reaching for the second (can you say fuse)!
At a minimum I would flag all antenna elements within reach with "CAUTION" tape - or better yet, roped them off. Caution tape can be purchased at very reasonable prices from hardware stores and should be in every ham's "go bag" along with a few 4-foot pieces of rebar and hammer. This is also a good reason to sanction public events through a club that carries liability insurance.
All in all, this event was great fun and very interesting. Our club members must have had a good time because they voted to host another KØS station next year. When the local newspaper came to visit our Field Day site they still remembered the strange antennas and were curious if any were present. I've also overheard a number of hams discussing KØS on local repeaters. I would certainly recommend others sponsor similar events because it seems to have captured the imagination of many.
Despite the formidable weather several of our primary objectives were achieved:
Interested parties can find additional information at my web site (www.nØew.org). Remember to send out those press releases, and I'll listen for you next year!
Erik Weaver, nØew
erik@nØew.org