2004 KØS, Kurt N. Sterba Strange Antenna Challenge

Breakout Connections

   I will begin by giving you a one-paragraph crash course in antenna connections, which will be followed by a one-paragraph introduction to each type of antenna mentioned in the previous paragraph. Each of these introductions to "real" antennas will be followed by a one-paragraph comparison to a "strange" antenna of the same type. I will also have a one-paragraph discussion of transmission line. Finally I will step you through a typical antenna hook up we used during the K0S Strange Antenna Challenge, starting from the power source to the transceiver and transmatch and ending with the connections to the strange antenna itself. To read a more complete explanation of these concepts, see my "K0S Field Manual" (about 5 MB PDF download).

   Let's begin with the smallest bit of theory possible!

   This is important: every antenna requires two connections. You may think of one as the "ground" and one as the "positive" if you like. Right now the terms really don't matter so long as you realize that you must have two connections leading from your antenna back to your transceiver. This is true as much for "real" antennas as it is for "strange antennas" and it is true for all types of antennas. If your antenna is comprised of very similar things you can think of it as a dipole, if it is comprised of one thing, you may think of it as a loop, and if it is comprised of very dissimilar things you may think of it as a vertical antenna, despite its actual orientation to planet earth. In all cases, you are required to have two connections to your antenna. The electrons from which your RF signal radiates travel along these two paths, and physics dictates there be two paths along which they may travel. It is in your best interest to think about this ahead of time and provide two paths along which the electrons may efficiently travel. Your antennas, be they strange or normal, will thank you!

Transmission line...
   There are two basic types of transmission line: coax and ladder line. Coax is round with a wire in the center (called the center conductor - it is the first wire), surrounded by some insulation, around which is wrapped a layer of metal (called braid, or shielding - this is the second "wire"). The outer-most layer is a thin layer of plastic to offer some protection to the shielding. The second type of transmission line is called ladder line (also known as twin lead, window line, balanced line, or open wire). In its most basic shape this is simply two lengths of bare metal wire separated an equal distance from each other for their entire run by an occasional piece of insulation, such as a plastic bar or rod (open wire). Other designs enclose these two bare wires with plastic (twin lead), and sometimes there are open spaces between the wires (window line, because they sort of look like a row of little windows). The coax metal shielding keeps your radio signal inside the coax until it is connected to your antenna, which then allows it to radiate. Ladder line (and its cousins) keeps your radio signal intact by maintaining equal spacing between the two wires for the entire run. As soon as the two wires are separated by a different distance, or come too close to a metal or magnetic object, they begin to radiate your radio signal. If all goes well, this will not take place until they reach the point where they are connected to your antenna wires.

Dipole...
   A standard "real" dipole antenna has two lengths of wire that are each 1/4 (25%) of one wavelength long. These are separated from each other by a short distance where they connect to the transmission line (coax or ladder line). A dipole is considered "ground independent" so it doesn't matter which of your two transmission line wires connects to which antenna wire. Each wire will run directly away from the other. The most important part of this antenna is the place where it connects to the transmission line (called the feedpoint) - get this as high above planet earth as possible (be certain it is well supported and can NOT fall into any power lines - this is true of all antennas).

   In the 2004 K0S we used two dipole configurations: a pair of trucks, and a pair of loadlocks (two 9-foot pieces of square metal tubing truck drivers use to hold their loads stationary inside their trailers). Each truck had a 2 inch receiver to which served as the antenna connection point (feedpoint). The loadlocks were connected to the transmission line at the ends that were placed beside one another.

Loop...
   A standard "real" loop antenna is just what is sounds like. It is a single wire that may be either orientated horizontally or vertically. The longer the wire and the closer it comes to making a perfect circle the better it normally performs (although almost all designs call for its shape to be either a square or triangle because we have to figure out some way of holding the wire up in the air). This is also considered to be a "ground independent" antenna, meaning you can connect either wire of your transmission line to either end of the long loop wire. As with the dipole, get up as high above the earth as you can safely manage.

   We used one loop in the 2004 K0S event. A roll of chicken wire was suspended from two tree branches with the free ends pulled towards one another at the bottom. The coax center conductor was connected to one end of the chicken wire and the coax shielding was connected to the other end of the chicken wire.

Vertical...
   A standard "real" vertical antenna is almost exactly what is sounds like. It has one wire (or metal pipe) pointing straight up towards the sky, and is usually 1/4 wavelength in height. This wire is connected to the center conductor of your coax. The shielding of the coax is connect to what is called a ground plane or radials (if connected by ladder line, connect the side of the ladder line that connects to your transmatch's ground lug to the vertical's ground plane). These are both the same thing - long lengths of wire - but if raised above the earth it is called a ground plane, and if placed along the earth it is called a radial system, or simply radials. For now I will use either term interchangeably. The more radials the better. Four are pretty good, one is better than none, and after you have 32, adding anymore is approaching the point of diminishing returns and generally not worth the extra trouble and expense. A gigantic sheet of copper would be nearly perfect, but is obviously not practical.

   A vertical antenna may either be mounted on the earth or in the air. In both cases it will need it ground plane or radials. If mounted on the earth, the ground radials are critical for achieving good performance. If mounted in the air, you still need the radials / ground plane, but not you will also benefit from getting the feedpoint as high as you may safely do so.

   Two vertical antennas were used in the 2004 K0S event. In the first case one loadlock was tied to a fiberglass step ladder to which the center conductor of the coax was connected. The shielding of the coax was connected to a neighborhood chain link fence which served as the ground plane. In the second case a length of chicken wire was rolled into a tube and suspend from a tree branch. This chicken wire was connected to the center conductor of the coax, and the coax shielding was connected to the same chain link fence as was the loadlock vertical.

Typical Portable Station Set-Up...

   We will begin with the battery connections. To make interconnections easier, I have made a small plastic box that has a switch in it that allows me to break (open circuit) the connection between the battery and this plastic box. On the other side of the switch I have a binding post to which I can connect the power leads for my transceiver. Once the power leads are connected to the radio and plastic box I can either provide battery power to the transceiver by closing the switch or cut the power by opening the switch.

   I hammer a metal tent stake into the earth by the table upon which I will set up my radio station. This stake has a short length of wire connected to it which is in turn connected to the grounding lugs of my transceiver and transmatch (antenna tuner). (If you run a generator you should make a similar connection to the earth and its frame.)

   On my operating table I have my transceiver and transmatch. Follow your transmatch directions for proper connections. We used a MFJ transmatch. This antenna tuner requires a short length of coax to connect the antenna output of the transceiver to the "transmitter" connection on the transmatch. (If you have more than one antenna output terminal - most likely a SO-239 - on your transceiver you may wish to take an additional short length of coax and connect a dummy load to each output terminal that is not connected to an antenna; this will protect your transceiver should you inadvertently transmit into the wrong antenna output terminal on your transceiver.)

   The transmatch has two antenna coax connections and one ladder line connection. These connections are where your antenna is connected to the transmatch. (You may wish to connect a dummy load to the connections you do not use, for the same reason you did with the transceiver.) So we would not get confused over the course of the weekend we always connected our strange antennas to the "coax 1" connection on the back of the transmatch.

   At this point our radio station is set up pretty much just like it would be inside your shack. Unless you are new to the amateur radio service all of the above was old-hat.

Strange Antenna Set-Up...

   We begin by connecting one end of a 100-foot length of RG-58 coax to the "coax 1" connection on the back of the transmatch (antenna tuner).

   On the far end of this length of coax we encounter a plastic coffer jar (sans coffee). Ten turns of coax as snuggly wrapped around this coffee can and taped into place. This is called a COAX CHOKE.

   The purpose of this is to restrain any stray RF energy from flowing away from the antenna along the outside of the coax shielding. Recall I said all antennas want two paths for their electrons to flow along? If you don't have this coax choke in place, and if the antenna does not present a good match (it most likely will NOT because it is a "strange" antenna, not a "real" antenna), some of this precious RF energy will "leak" away! This coax choke helps to prevent this, and keeps the energy where we want it - inside the antenna and coax.

   Another device that performs a similar function is what is generically called a "balun" (there are actually several types of these, none of which we will discuss here - see my "K0S Field Manual" for additional information). There are two designs; a "voltage" balun and a "current" balun. You will almost always find the current balun works best in amateur radio applications.

   You may have noticed the Altoid's Mint can in the previous picture. You can see the coax is connected to this can (it is attached to a coax SOcket, SO-239). You can also see the red and black binding post mounted near the SO-239. Inside the Altoid's can there are two short pieces of # 12 wire. One connects the coax center conductor (via the SO-239) to the red binding post, and the other connects the coax shielding to the black binding post. Just as with your transceiver and transmatch, the body of the mint can is the "ground" which maintains a direct connection to your coax shielding through the SO-239 and PL-259 (the coax PLug, PL-259). I knew I would often use this breakout box outdoors, so after I soldered all the connections, tested them, and let them cool down, I filled the Altoid's can with silicon. This provides a water-proof barrier and also helps hold everything in place as I bang it across the state!

   Leading from the Altoid's breakout can are two blue wires (# 12 stranded). Each end has been stripped of insulation for 1/2 to 3/4 inch. As you can see, one is attached to the red binding post and the other is attached to the black binding post. Try to keep these breakout wires as short as possible. (I carry two sets with me for the strange antenna challenge, one set is about 14 inches and the other is about 8 inches long.)

   If you are hooking up to a loop or dipole style antenna it doesn't matter which lead is connect to which side of your strange antenna. If however, you are connecting to a vertical style antenna you will want to connect the red binding post (and therefore the center conductor of your coax) to the vertical element, and the black binding post to the ground plane (or radials).

   Here you can see a typical ground plane connection. The wire leading from the black binding post is sandwiched between the metal rail of a chain link fence and the hose clamp. The hose clamp is then tightened to produce a good electrical connection between the wire and the fence rail. This particular fence runs along the entire length of the block, and is an excellent ground plane! This is fairly common even for those using a "normal" vertical antenna. I personally know several hams that have done this and they each report it works quite well.

   Next I will show you two typically connections to strange antennas themselves. In one case we are connecting to a piece of square metal tubing, so we just need a hose clamp to secure a good electrical connection (although some people like to scrape away any paint or rust from whatever they are connecting).

   As an aside, note the hose clamp's position on the end of the yellow square tubing. If you alter the position of this hose clamp, either up or down, you will find the impedance is changed. If you are having trouble getting a successful tune on a strange antenna, adjust the point(s) at which you are attaching to the strange antenna.

   The other image shows how to connect to a strange antenna that does not have as much strength, and which tightening the hose clamp may actually damage. To avoid such damage and to ensure we can get a firm bite by the hose clamp I insert a plastic dog bone insulator inside the hose clamp. This allows me to sandwich the breakout wire between the metal of the strange antenna and the dog bone, creating the required electrical connection.

   And that is about it! Not too tricky really. One of the biggest points to keep in mind is every antenna requires two connections with your transmission line, and your transmission line requires two connections to your transmatch / transceiver. As I said earlier, this is critical.

   Did I hear someone ask about longwires, and say they only have one wire and therefore one path?

   This is not entirely true. True, there is one antenna element, the longwire that runs from your station to whatever holds it up in the air. However, while there may not be a physical wire that serves as the return path (the second path) for your RF energy (the friendly electrons we spoke of earlier), the second path DOES EXIST. But where? It is the earth itself! Now the earth is not a very good conductor of RF energy (there are exceptions, such as flooding your yard with salt water, but not too many people do this). Some earth provides a better return path (RF conductivity) than other ground. Sometimes a fairly good return path lies right beneath your feet and at other times it is a miserable conductor.

   In any event, when you see an antenna design with no apparent "second wire" look more closely. Often you'll discover that planet earth herself is expected to act as the missing conductor.

   Before leaving the subject of planet earth as a conductor for RF energy, let's touch upon the subject of ground radials. Do NOT bury them very deep. An inch is fine. A foot is too deep, and if you can get away with it, just lay the, on the ground. By and by the grass will grow over them and keep them safely away from your lawn mower. You may not want to let your kids play out in the rain while you are operating however!