I can’t believe it has been a year. My, how time flies when you’re having fun. For those that I haven’t bored to death, or lost completely, welcome, and I am in hopes that this year may be better for us than this past year.

    Listening to HF and VHF frequencies while I work in the shop, I have been hearing a lot of discussion on antennas. Seems the most favorite is the G5RV (designed in England by Louis Varney (G5RV) some years ago). It is a good antenna, and on 20-meters is of course longer than a standard half wave dipole and it exhibits about 2 db more gain compared to that
dipole.

    For this reason, and the fact that most hams are like me broke and can’t afford big yagi antennas to run with the big boys, then this is the poor man’s special. In this article, I will discuss the building of a G5RV from scratch, and how to use them with a manual tuner, or how they can be used with an autotuner.
 
    “What’s that,” you say, “My G5RV works with my auto-tuner, does it?” What makes it work with an auto-tuner is a device known as a balun. What is a balun? Let’s find out.

    BALUN: Meaning: BAL for Balanced and Un for Unbalanced
    
    Am I playing both sides of the fence with this “Balanced and Unbalanced”? No, believe it or not, they both work together (I wish my checkbook did the same thing…)

    A balun is a device that is used at the feedpoint of a balanced antenna when an unbalanced feedline is used to feed the antenna. A common example of where a balun would be used is at the feedpoint of a dipole antenna when a coaxial transmission line is used. If a balun is not used it is possible for common mode currents to be present on the feedline. The effect of this could be undesirable if the directional properties of the balanced antenna are to be maintained. Since the feedline usually leads into the shack, RF could be present in the shack to create RFI (Radio Frequency Interference) as well as the possibility of receiving excessive amounts of RFI from indoor noise sources.
    
    It is often found that a balun is not necessary and everything works just fine feeding the balanced antenna directly with coax cable. When this is possible it may be found that the feedline is an odd multiple of one-quarter wavelength. In this case the transmitter end of the feedline is usually grounded and from this point on the coax which is one-quarter wavelength or a multiple thereof will appear as a high impedance.

    When this high impedance point occurs at the feedpoint, chances of common mode currents are low. Rather than take any chances it is often recommended to use a balun. There are several different kinds of baluns. Some provide a 1:1 impedance ratio while others can provide 1:1.5, 1:4, or many other impedance ratios. A 1:4 ratio balun would come in handy if you were feeding a folded dipole (200 ohms) with 50 ohm coax.

    A simple 1:1 ratio balun can be constructed using the feedline itself by simply winding about five turns of the feedline around a 2” diameter piece of PVC. In that case, the 1:1 balun could easily be moved from one antenna to another by simply unscrewing the coax. If you have followed my previous discussions on antennas and dipoles, you will remember that a simple dipole will show an impedance of 200 ohms at the feedpoint. To feed this with a 50 ohm coax cable, do the math. If you divide 200 by 50, you end up with 4, thereby telling you that you would need a 4 to 1 ratio, or a 4:1 balun. Of course not all antenna impedances are 200 ohms, thereby telling us that whatever the proposed impedance is, we must construct a balun that will give us the impedance that we need.


    By far, the simplest balun you can construct, and by far the cheapest, is a 4:1 design. Depending on how much power you plan to run, most of these baluns are made from #14
or #12 Romex. If you aren’t familiar with Romex, it is the common house wiring used in your house. (I hope you have #12 in your house). It is fairly cheap, and can be purchased at any
electrical supplier such as Home Depot, Lowes, etc… Or maybe you have a friend that does electrical work that would be happy to give you some scrap. I like to use Romex due to the
simple fact that you have two colors (black and white).

    This makes it easy so that construction is easier. Using #14, your balun can handle up to 400 watts. Using #12 puts you at 650 to 700 watts, and if you use #10, you can run the legal limit. I mentioned this balun first, for it can be used with your G5RV construction. As you can see from the photo, connecting the ladder line to the balun allows you to run coax into the shack to your manual or auto-tuner. If you have a manual tuner, then just bring the ladder line directly to the tuner, because it has a balun built in. Using your imagination, you can construct this type of balun inside a piece of PVC pipe, with two end caps, and it will look store-bought. Since these are so simple, I recommend that one be used with all dipole antennas, “Why take a chance...”

    That will stop the dreaded, “... if I had only ...” later.

    For those RICH operators, this balun is a must. When you install that 5-element 80-meter monobander, or that stack four array of 5-element 20-meter yagi’s, or any other BALANCED antenna, this is the one for you.

    For best construction of this balun, use AWG #12 enameled wire. You will need enough wire to make seven turns three times on a 6” X ½” ferrite rod ( which can be found in hobby shops).

    Once again to keep from getting confused, I use some way to color code the three different wires. You can use tape, red, white, and blue, or I like to use heat shrink tubing because it bonds and won’t come off. The free ends of the windings are connected as follows: You will have two binding posts at the top, and a SO-239 at the bottom.

    Once again using a 10” long piece of one and a half-inch schedule 40 PVC and the matching end caps, it is weather proofed, and looks factory made. If you don’t like the idea of PVC construction, then there is an alternate balun using a device known as a toroid.

    If you could take the ferrite rod that we just mentioned, and bend it in a circle, you would pretty much have a toroid. However, since I don’t know how to do this, then we will use one that is manufactured by someone that does.

    Toroids come in many sizes and shapes, and are used not only in antenna work, but in just about all the radio equipment manufactured today. Basically, a toroid allows use to create a large inductance, while at the same time, remaining physically small for easy use in an antenna.

    For example, if I were making a coil to use on 40-meters in a tank circuit, for less than 10 watts, I would need a 1” coil made with 20½ turns of #20 enamel wire. The same can be accomplished with a toroid about the size of a Cheerio with 10 or 12 turns of #28 wire. Look at the construction of a balun formed on a toroid below:

    Many modern HF transceivers come fully equipped with built-in tuners. While these tuners are great for changing bands, the manufacturers left out a very important accessory: the 4 to 1 balun. Without a balun the transceiver can only feed an antenna which uses coaxial cable. While this may be satisfactory for some operators, this is a real problem for those of us who  prefer the super low loss ladder line.

    The only other alternative is to buy an external tuner with a built-in balun which is really absurd after spending the additional money to have one built into the radio. Fortunately, a 4 to 1 balun can be easily home brewed as illustrated. The list below shows how you can choose the wattage rating, and what you need for the construction:

TOROID           NUMBER OF TURNS                POWER RATING
T80-2                         25                                         60 watts
T106-2                       16                                         100 watts
T130-2                       18                                         150 watts
T157-2                       16                                         250 watts
T200-2                       17                                         400 watts
T200A-2                     13                                         400 watts
T400-2                       14                                         1000 watts

    The exact number of turns is not critical but the numbers listed in the preceding table should yield optimum results. It is possible to exceed the power ratings listed above but the performance of the balun may be degraded during high SWR causing heating of the core.

    Toroids of this type are available from a number of dealers, but for the quality and price, I would use Allied Electronics, or DigiKey. The baluns should be housed in a suitable weather-proof housing. You can use plastic weather-proof boxes from electrical suppliers for construction, or use PVC as mentioned previously.

    Well, now that I have bored you again, I will close this session, and begin working on the next. Until then, remember, “ May your QSO’s be long, and your coax short “.

    A wise man once said, “Waste not, want not,” and while the saying has no doubt been used to collect some pretty silly things at times, there is little doubt that it can prove fruitful for the ham operator. One example played out this week as I built two antennas for use at the shack.


    ‘Wasting not’ came in the form of collecting an old damaged television antenna from someone who was otherwise just going to throw it away. While the bent, broken, and in some cases, missing elements made it nearly worthless for receiving television signals, the square tube aluminum boom almost shouted out to the homebuilder to give it a new life as a yagi antenna and rescue it from it’s destiny in the landfill.

    The television antenna actually consisted of two booms - a longer two-part boom that was about 15 feet long, and a lower brace boom that was about seven feet long.
With dreams of a high-gain yagi sniffing out faint signals running through my head, I lashed the antenna on the roof-rack of my Jeep and headed off to see our local antenna guru - Jim Searcy (WA5WRE). His eyes brightened as he took a look at the find, and we started planning the construction.

    After some consideration of such concerns as materials, size, weight, etc. - I decided to scale back from the 21-element yagi I had imagined - and we decided on a six-element version of a traditional design. The lower brace tubing would serve as the boom, and some one-half-inch aluminum tubing would be trimmed for elements. A old gamma-match would serve to move signal to air, and with some labor and luck - my new antenna would become a reality.
    
    Building an antenna with Jim is a learning experience - as those who have shared his shop can attest. An old-time-ham, he believes in not only good design and construction, but also in understanding the WHY of how an antenna is designed and built. The experience can be challenging, entertaining, and is always informative. First step is always research. Specifics such as boom length, element length, spacing and number have to be determined, as well as type of match and intended application.
    
    Once these decisions were made, it was time to start fabricating. The lower brace tube was easily unfastened from the upper boom, and a quick bump with a drill press was all it took to remove the old rivets in the boom that were in the way.

     “It can’t just work good - it has to look good too,” commented Jim - so we spent some time running the boom and the elements through a wire-wheel mounted on a bench grinder. The resulting “brushed aluminum” look is pleasing and in fact more efficient because the oxidized metal of the boom and elements have been removed.
    
    Once they were prepared, it was time to start to make measurements and cuts. A “Sharpie” is a good way to make the marks on the boom and the elements to indicate lengths, placements for holes, etc. See the chart below for the measurements we used.

Reflector     Driven Element       Director #1       Director #2           Director #3        Director #4
40 5/16"            38"                     37 1/8"             36 1/8"                35 1/4"            35 3/16"

    The boom conveniently had a hole already drilled about one-inch in from one end, so we used that as a starting point. Based on a design from a widely available yagi, we measured from the center of the first hole and made marks for the holes of the rest of the holes for element mounting.

The holes were placed as follows:

Reflector            Driven to            Director #1 to        Director #2 to        Director #3 to      
to Driven            Director #1            Director #2           Director #3           Director #4
13 1/2"                 9"                         14 1/2"                    14"                     16"

    The trusty drill press again worked its magic and 3/16" holes were drilled through the boom at the marked locations. Once we knew where the last element would mount, we measured another inch beyond that point and cut off the boom for a final length of 5'4" (64") long. We put the drill press back into action to drill 3/16" holes at the exact center of each element, then mounted each element to the boom in place with small (10-24) hardware.

    With all the elements mounted and checked for alignment, it was time to take the yagi outside for a brief test. It was cold outside - so I know we must have looked a sight - me holding
the beam antenna overhead and Jim with the trusty MFJ 269 Antenna Analyzer checking SWR. After a few minor adjustments, we achieved an almost perfect match - 1.1-1 SWR at 146.100 Mhz.

    Time then to check performance. We didn’t want to mount it on a pole, so we lifted the yagi overhead and twisted back and forth in what we guessed was the correct direction for several local repeaters. One thing we found is that the pattern is very narrow - if you get more than about 10 degrees off pointing directly at the signal source, the signal drops from full
scale to about a one. All-in-all, a definite success, and I am looking forward to getting my hands on a rotor to mount it at home for regular use.

    And the sections of boom that Jim kept? “You’ll have to wait and see what I build with that,” was his cryptic comment.


    The yagi described above was not the only creation of the week. I also had the chance to put together an 80-Meter dipole out of some old wire, an SO-239 connector and a small piece of lexan as the center section.
    
    The first step was to cut the legs for the antenna. Using the old formula that should be familiar to every person holding even a technician class license, (468 divided by frequency in Megahertz, I quickly determined that the antenna would be 133.71 feet long. Dividing by two, we see that each leg would be 66.86 feet long.

    Because I plan to hang the antenna in an “Inverted ‘V’”, however, I know to subtract 1.5% of length from each leg. Doing the math quickly, that left each leg at 65.85 feet. I measured out the wire, (14 gauge stranded - insulated) and cut each leg at 66 feet - leaving about two inches per leg for trimming and attachments.

    I then turned my attention to the center section. The first step was to drill out the space for the SO-239 connector to sit in the middle of the lexan. Using a Forstner bit, I made a hollowed-out area for the SO-239, then switched to a smaller bit for the center hole for the connector. The center punch hole from the Forster bit made centering the smaller hole easy - and a clean hole straight through the lexan was quickly achieved. Two smaller holes were drilled out for the mounting hardware for the SO-239, as well as smaller holes about one-inch from the outside edge of the lexan for the leg mountings.

    The SO-239 was bolted into place, and a short wire jumper was soldered to the center pin of the SO-239, and it terminated at one of the leg mounting bolts. Another wire jumper runs from one of the SO-239 mounting bolts to the other leg mounting point.The legs were then attached using ring connectors to the leg mounting points, and after a generous covering of clear silicone was applied to seal the back of the SO-239, the dipole is ready to be mounted and used.

    A quick raid on the old junkbox turned up two old cable reliefs that were pressed into service as ends for the dipole legs. They provide a place to tie off the legs without taking the chance that the legs will break due to bending strain. The only addition planned from the picture, right, is the addition of strain relief where the legs leave the edge of the center piece of lexan. These will be made from large eye-connectors.